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Schistosomiasis, also known as snail fever, bilharzia, and Katayama fever, is a
disease A disease is a particular abnormal condition that negatively affects the structure or function (biology), function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medica ...
caused by
parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...
flatworm The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") are a phylum of relatively simple bilaterian, unsegment ...
s called
schistosome ''Schistosoma'' is a genus of trematodes, commonly known as blood flukes. They are parasitic flatworms responsible for a highly significant group of infections in humans termed ''schistosomiasis'', which is considered by the World Health Organi ...
s. The
urinary tract The urinary system, also known as the urinary tract or renal system, consists of the kidneys, ureters, bladder, and the urethra. The purpose of the urinary system is to eliminate waste from the body, regulate blood volume and blood pressure, co ...
or the
intestines The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...
may be infected. Symptoms include
abdominal pain Abdominal pain, also known as a stomach ache, is a symptom associated with both non-serious and serious medical issues. Common causes of pain in the abdomen include gastroenteritis and irritable bowel syndrome. About 15% of people have a more ...
,
diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin wi ...
, bloody stool, or
blood in the urine Hematuria or haematuria is defined as the presence of blood or red blood cells in the urine. “Gross hematuria” occurs when urine appears red, brown, or tea-colored due to the presence of blood. Hematuria may also be subtle and only detectable w ...
. Those who have been infected for a long time may experience liver damage,
kidney failure Kidney failure, also known as end-stage kidney disease, is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney failure is classified as ei ...
,
infertility Infertility is the inability of a person, animal or plant to reproduce by natural means. It is usually not the natural state of a healthy adult, except notably among certain eusocial species (mostly haplodiploid insects). It is the normal stat ...
, or
bladder cancer Bladder cancer is any of several types of cancer arising from the tissues of the urinary bladder. Symptoms include blood in the urine, pain with urination, and low back pain. It is caused when epithelial cells that line the bladder become mal ...
. In children, it may cause poor growth and learning difficulty. The disease is spread by contact with
fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does includ ...
contaminated with the parasites. These parasites are released from infected
freshwater snail Freshwater snails are gastropod mollusks which live in fresh water. There are many different families. They are found throughout the world in various habitats, ranging from ephemeral pools to the largest lakes, and from small seeps and spring ...
s. The disease is especially common among children in developing countries, as they are more likely to play in contaminated water. Other high-risk groups include farmers, fishermen, and people using unclean water during daily living. It belongs to the group of helminth infections. Diagnosis is by finding eggs of the parasite in a person's urine or stool. It can also be confirmed by finding
antibodies An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...
against the disease in the blood. Methods of preventing the disease include improving access to clean water and reducing the number of snails. In areas where the disease is common, the medication
praziquantel Praziquantel (PZQ), sold under the brandname Biltricide among others, is a medication used to treat a number of types of parasitic worm infections in mammals, birds, amphibians, reptiles, and fish. In humans specifically, it is used to treat sc ...
may be given once a year to the entire group. This is done to decrease the number of people infected, and consequently, the spread of the disease. Praziquantel is also the treatment recommended by the
World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of ...
for those who are known to be infected. Schistosomiasis affected about 236.6 million people worldwide in 2019. An estimated 4,400 to 200,000 people die from it each year. The disease is most commonly found in Africa, Asia, and South America. Around 700 million people, in more than 70 countries, live in areas where the disease is common. In tropical countries, schistosomiasis is second only to
malaria Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or deat ...
among parasitic diseases with the greatest economic impact. Schistosomiasis is listed as a
neglected tropical disease Neglected tropical diseases (NTDs) are a diverse group of tropical infections that are common in low-income populations in developing regions of Africa, Asia, and the Americas. They are caused by a variety of pathogens, such as viruses, bacte ...
.


Signs and symptoms

Many individuals do not experience symptoms. If symptoms do appear, they usually take 4–6 weeks from the time of infection. The first symptom of the disease may be a general feeling of illness. Within 12 hours of infection, an individual may complain of a tingling sensation or light
rash A rash is a change of the human skin which affects its color, appearance, or texture. A rash may be localized in one part of the body, or affect all the skin. Rashes may cause the skin to change color, itch, become warm, bumpy, chapped, dry, cr ...
, commonly referred to as "
swimmer's itch Swimmer's itch, cercarial dermatitis or schistosome dermatitis is a short-term allergic contact dermatitis occurring in the skin of humans that have been infected by water-borne schistosomes, a type of flatworm. It is common in freshwater, bracki ...
", due to irritation at the point of entrance. The rash that may develop can mimic
scabies Scabies (; also sometimes known as the seven-year itch) is a contagious skin infestation by the mite '' Sarcoptes scabiei''. The most common symptoms are severe itchiness and a pimple-like rash. Occasionally, tiny burrows may appear on the skin ...
and other types of rashes. Other symptoms can occur 2–10 weeks later and can include
fever Fever, also referred to as pyrexia, is defined as having a temperature above the normal range due to an increase in the body's temperature set point. There is not a single agreed-upon upper limit for normal temperature with sources using val ...
, aching, a
cough A cough is a sudden expulsion of air through the large breathing passages that can help clear them of fluids, irritants, foreign particles and microbes. As a protective reflex, coughing can be repetitive with the cough reflex following three ph ...
,
diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin wi ...
, chills, or gland enlargement. These symptoms can also be related to avian schistosomiasis, which does not cause any further symptoms in humans. The manifestations of schistosomal infection vary over time as the cercariae, and later adult worms and their eggs, migrate through the body. If eggs migrate to the brain or spinal cord, seizures, paralysis, or spinal-cord inflammation are possible.


Acute Infection

Manifestation of acute infection from schistosoma include cercarial dermatitis (hours to days) and acute schistosomiasis (2–8 weeks).


Cercarial dermatitis

The first potential reaction is an itchy,
maculopapular A maculopapular rash is a type of rash characterized by a flat, red area on the skin that is covered with small confluent bumps. It may only appear red in lighter-skinned people. The term "maculopapular" is a compound: '' macules'' are small, flat ...
rash that results from cercariae penetrating the skin within the first 12 hours to days of cercarial skin penetration. The first time a non-sensitized person is exposed, the rashes are usually mild with an associated prickling sensation that quickly disappear on its own since this is a type of hypersensitivity reaction. In sensitized people who have previously been infected, the rash can develop into itchy, red, raised lesions (
papule A papule is a small, well-defined bump in the skin. It may have a rounded, pointed or flat top, and may have a dip. It can appear with a stalk, be thread-like or look warty. It can be soft or firm and its surface may be rough or smooth. Some h ...
s) with some turning into fluid-filled lesions ( vesicles). Previous infections with cercariae causes a faster developing and worse presentation of dermatitis due to the stronger immune response. The round bumps are usually one to three centimeters across. Because people living in affected areas have often been repeatedly exposed, acute reactions are more common in tourists and migrants. The rash can occur between the first few hours and a week after exposure, and they normally resolve on their own in around 7–10 days. For human schistosomiasis, a similar type of
dermatitis Dermatitis is inflammation of the skin, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened. The area of skin involved can ...
called "swimmer's itch" can also be caused by cercariae from animal trematodes that often infect birds. Cercarial dermatitis is not contagious and can not be transmitted from person-to-person. Symptoms may include: * Flat, red rash * Small red, raised pimples * Small red blisters * Prickling or tingling sensation, burning, itching of the skin Scratching the rash can lead to secondary bacterial infection of the skin, thus it is important to refrain from scratching. Some common treatments for itching include corticosteroid cream, anti-itch lotion, application of cool compresses to rash, bathing in Epsom salts or baking soda, and in severe itching cases, prescription strength cream and lotions. Oral
antihistamine Antihistamines are drugs which treat allergic rhinitis, common cold, influenza, and other allergies. Typically, people take antihistamines as an inexpensive, generic (not patented) drug that can be bought without a prescription and provide ...
s can also help relieve the itching.


Acute schistosomiasis (Katayama fever)

Acute schistosomiasis (Katayama fever) may occur weeks or months (around 2–8 weeks) after the initial infection as a systemic reaction against migrating schistosomulae as they pass through the bloodstream through the lungs to the liver and also against the antigens of eggs. Similarly to swimmer's itch, Katayama fever is more commonly seen in people with their first infection such as migrants and tourists, and it is associated with heavy infection. It is seen, however, in native residents of China infected with '' S. japonicum''. ''S. japonicum'' can cause acute schistosomiasis in chronically infected population, and it can lead to a more severe form of acute schistosomiasis. Symptoms may include: * Dry cough with changes on
chest X-ray A chest radiograph, called a chest X-ray (CXR), or chest film, is a projection radiograph of the chest used to diagnose conditions affecting the chest, its contents, and nearby structures. Chest radiographs are the most common film taken in med ...
* Fever *
Fatigue Fatigue describes a state of tiredness that does not resolve with rest or sleep. In general usage, fatigue is synonymous with extreme tiredness or exhaustion that normally follows prolonged physical or mental activity. When it does not resolve ...
* Muscle aches * Headache * Malaise * Abdominal pain * Diarrhea * Enlargement of both the liver and the spleen * Hives Acute schistosomiasis usually self-resolves in 2–8 weeks in most cases., but a small proportion of people have persistent weight loss, diarrhea, diffuse abdominal pain, and rash. Complications may include: * Spinal cord inflammation (
transverse myelitis Transverse myelitis (TM) is a rare neurological condition wherein the spinal cord is inflamed. The adjective ''transverse'' implies that the spinal inflammation (myelitis) extends horizontally throughout the cross section of the spinal cord; t ...
) may occur if worms or eggs travel to the spinal cord during this acute phase of infection. Treatment may include: *
Corticosteroid Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are invo ...
such as
prednisone Prednisone is a glucocorticoid medication mostly used to suppress the immune system and decrease inflammation in conditions such as asthma, COPD, and rheumatologic diseases. It is also used to treat high blood calcium due to cancer and adre ...
is used to alleviate the hypersensitivity reaction and reduce inflammation *
Praziquantel Praziquantel (PZQ), sold under the brandname Biltricide among others, is a medication used to treat a number of types of parasitic worm infections in mammals, birds, amphibians, reptiles, and fish. In humans specifically, it is used to treat sc ...
can be administered to kill the adult schistosomes to prevent chronic infection in addition to corticosteroid therapy. It is not effective to recent infection as it only targets the adult worms, but not the premature schistosomulae. Therefore, a repeat treatment of praziquantel several weeks after initial infection may be warranted. It is recommended to treat with praziquantel 4–6 weeks after initial exposure since it targets adult worms.


Chronic infection

In long-established disease, adult worms lay eggs that can cause inflammatory reactions. The eggs secrete
proteolytic Proteolysis is the breakdown of proteins into smaller polypeptides or amino acids. Uncatalysed, the hydrolysis of peptide bonds is extremely slow, taking hundreds of years. Proteolysis is typically catalysed by cellular enzymes called proteases, ...
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. ...
s that help them migrate to the bladder and intestines to be shed. The enzymes also cause an
eosinophilic Eosinophilic (Greek suffix -phil-, meaning ''loves eosin'') is the staining of tissues, cells, or organelles after they have been washed with eosin, a dye. Eosin is an acidic dye for staining cell cytoplasm, collagen, and muscle fibers. ''Eosi ...
inflammatory reaction when eggs get trapped in tissues or embolize to the liver, spleen,
lung The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side ...
s, or
brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in ...
. The long-term manifestations are dependent on the species of schistosome, as the adult worms of different species migrate to different areas. Many infections are mildly symptomatic, with
anemia Anemia or anaemia (British English) is a blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin. When anemia comes on slowly, ...
and
malnutrition Malnutrition occurs when an organism gets too few or too many nutrients, resulting in health problems. Specifically, it is "a deficiency, excess, or imbalance of energy, protein and other nutrients" which adversely affects the body's tissues ...
being common in endemic areas.


Intestinal schistosomiasis

The worms of '' S. mansoni'' and ''S. japonicum'' migrate to the veins of the gastrointestinal tract and liver. Eggs in the gut wall can lead to pain, blood in the stool, and diarrhea (especially in children). Severe disease can lead to narrowing of the colon or
rectum The rectum is the final straight portion of the large intestine in humans and some other mammals, and the gut in others. The adult human rectum is about long, and begins at the rectosigmoid junction (the end of the sigmoid colon) at the l ...
. In intestinal schistosomiasis, eggs become lodged in the intestinal wall during their migration from the mesenteric venules to the intestinal lumen, and the trapped eggs cause an immune system reaction called a granulomatous reaction. They mostly affect the large bowel and rectum, and involvement of the small bowel is more rare. This immune response can lead to obstruction of the colon and blood loss. The infected individual may have what appears to be a potbelly. There is a strong correlation between morbidity of intestinal schistosomiasis and the intensities of infection. In cases of light infections, symptoms may be mild and can go unrecognized. The most common species to cause intestinal schistosomiasis are ''S. mansoni'' and ''S. japonicum'', however, '' S. mekongi'' and '' S. intercalatum'' can also cause this disease. Symptoms may include: * Abdominal pain and discomfort * Loss of appetite * Mucous diarrhea with or without gross blood * Blood in feces that is not visibly present (fecal occult blood) * Abdominal distention Complications may include: * Intestinal polyps * Intestinal ulcers * Iron deficient anemia *
Fistula A fistula (plural: fistulas or fistulae ; from Latin ''fistula'', "tube, pipe") in anatomy is an abnormal connection between two hollow spaces (technically, two epithelialized surfaces), such as blood vessels, intestines, or other hollow or ...
* Bowel strictures (narrowing of colon or rectum) *
Protein-losing enteropathy Protein losing enteropathy refers to any condition of the gastrointestinal tract (e.g. damage to the gut wall) that results in a net loss of protein from the body. Signs and symptoms The signs/symptoms of protein losing enteropathy are consistent ...
* Partial or complete
bowel obstruction Bowel obstruction, also known as intestinal obstruction, is a mechanical or functional obstruction of the intestines which prevents the normal movement of the products of digestion. Either the small bowel or large bowel may be affected. Signs a ...
*
Appendicitis Appendicitis is inflammation of the appendix. Symptoms commonly include right lower abdominal pain, nausea, vomiting, and decreased appetite. However, approximately 40% of people do not have these typical symptoms. Severe complications of a ru ...
(rare) Approximately 10-50% of people living in endemic regions of ''S. mansoni'' and ''S. japonicum'' develop intestinal schistosomiasis. ''S. mansoni'' infection epidemiologically overlaps with high HIV prevalence in Sub-Saharan Africa, where gastrointestinal schistosomiasis has been linked to increased HIV transmission.


Hepatosplenic schistosomiasis

Eggs also migrate to the liver leading to fibrosis in 4 to 8% of people with chronic infection, mainly those with long-term heavy infection. Eggs can become lodged in the
liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...
, leading to
portal hypertension Portal hypertension is abnormally increased portal venous pressure – blood pressure in the portal vein and its branches, that drain from most of the intestine to the liver. Portal hypertension is defined as a hepatic venous pressure gradient ...
,
splenomegaly Splenomegaly is an enlargement of the spleen. The spleen usually lies in the left upper quadrant (LUQ) of the human abdomen. Splenomegaly is one of the four cardinal signs of ''hypersplenism'' which include: some reduction in number of circulatin ...
, the buildup of fluid in the abdomen, and potentially life-threatening dilations or swollen areas in the esophagus or gastrointestinal tract that can tear and bleed profusely (
esophageal varices Esophageal varices are extremely dilated sub-mucosal veins in the lower third of the esophagus. They are most often a consequence of portal hypertension, commonly due to cirrhosis. People with esophageal varices have a strong tendency to develop s ...
). This condition can be separated into two distinct phases: inflammatory hepatic schistosomiasis (early inflammatory reaction) and chronic hepatic schistosomiasis. Most common species to cause this condition are ''S. mansoni'', ''S. japonicum'', and ''S. mekongi''. Inflammatory hepatic schistosomiasis * This condition occurs mainly in children and adolescents due to early immune reaction to eggs trapped within the periportal and presinusoidal spaces of the liver creating numerous granulomas. Liver function is not affected, and the severity of liver and spleen enlargement is correlated to the intensity of the infection. It is characterized by an enlarged left lobe of the liver with a sharp edge and enlarged spleen with nodules. The enlargement of liver and spleen is usually mild, but in severe cases, they can enlarge to the level of the belly button and even into the pelvis. Chronic (fibrotic) hepatic schistosomiasis * This is a late stage liver disease that occurs mainly in young and middle-aged adults who have been chronically infected with a heavy infection and whose immune regulation of fibrosis is not functioning properly. It affects only a small proportion of people who are infected. Liver function and liver architecture are not affected unlike cirrhosis. The pathogenesis of this disease is caused by deposition of collagen and extracellular matrix proteins within the periportal space, which leads to liver portal fibrosis and enlarged fibrotic portal tracts (Symmer's pipe stem fibrosis). The periportal fibrosis physically compress the portal vein leading to
portal hypertension Portal hypertension is abnormally increased portal venous pressure – blood pressure in the portal vein and its branches, that drain from most of the intestine to the liver. Portal hypertension is defined as a hepatic venous pressure gradient ...
(increased portal venous pressure), increased pressure of the splenic vein, and subsequent enlargement of the spleen. Portal hypertension can also increase the pressure in portosystemic anastomoses (vessel connections between the portal circulation and systemic circulation) leading to esophageal varices and
caput medusae Caput medusae is the appearance of distended and engorged superficial epigastric veins, which are seen radiating from the umbilicus across the abdomen. The name ''caput medusae'' ( Latin for "head of Medusa") originates from the apparent simil ...
. These portosystemic anastomoses also allows a pathway for the eggs to travel to locations such as the lungs, spinal cord, or brain. Co-infection with hepatitis is common in regions endemic to schistosomiasis with hepatitis B or hepatitis C, and co-infection with hepatitis C is associated with more rapid liver deterioration and worse outcome. Fibrotic hepatic schistosomiasis caused by ''S. mansoni'' usually develops in around 5–15 years, while it can take less time for ''S. japonicum''. * Symptoms may include: **
Esophageal varices Esophageal varices are extremely dilated sub-mucosal veins in the lower third of the esophagus. They are most often a consequence of portal hypertension, commonly due to cirrhosis. People with esophageal varices have a strong tendency to develop s ...
(can cause life-threatening esophageal variceal bleed) **
Ascites Ascites is the abnormal build-up of fluid in the abdomen. Technically, it is more than 25 ml of fluid in the peritoneal cavity, although volumes greater than one liter may occur. Symptoms may include increased abdominal size, increased weight, ab ...
(end-stage) **
Caput medusae Caput medusae is the appearance of distended and engorged superficial epigastric veins, which are seen radiating from the umbilicus across the abdomen. The name ''caput medusae'' ( Latin for "head of Medusa") originates from the apparent simil ...
** Enlarged spleen and liver * Complications may include: ** Neuroschistosomiasis due to portosystemic anastomoses from portal hypertension ** Pulmonary Schistosomiasis due to portosystemic anastomoses from portal hypertension


Pulmonary schistosomiasis

Portal hypertension secondary to hepatosplenic schistosomiasis can cause vessel connections between the portal (liver and gut) circulation and systemic circulation to develop, which creates a pathway for the eggs and worms to travel to the lungs. The eggs can be deposited around the alveolar capillary beds and causes granulomatous inflammation of the pulmonary arterioles followed by fibrosis. This leads to high blood pressure in the pulmonary circulation system ( pulmonary hypertension), increased pressure in the right heart, enlargement of the pulmonary artery and right atria, and thickening of the right ventricular wall. Symptoms of pulmonary hypertension may include: * Shortness of breath * Chest pain * Feeling tired * Fainting during physical exertion


Urogenital schistosomiasis

The worms of '' S. haematobium'' migrate to the veins around the
bladder The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine enters ...
and
ureter The ureters are tubes made of smooth muscle that propel urine from the kidneys to the urinary bladder. In a human adult, the ureters are usually long and around in diameter. The ureter is lined by urothelial cells, a type of transitional ep ...
s where they reproduce. ''S. haematobium'' can produce up to 3000 eggs per day, these eggs migrate from the veins to the bladder and ureter lumens, but up to 50 percent of them can become trapped in the surrounding tissues causing granulomatous inflammation, polyps formation, and ulceration of bladder, ureter, and genital tract tissues. This can lead to
blood in the urine Hematuria or haematuria is defined as the presence of blood or red blood cells in the urine. “Gross hematuria” occurs when urine appears red, brown, or tea-colored due to the presence of blood. Hematuria may also be subtle and only detectable w ...
10 to 12 weeks after infection. Over time,
fibrosis Fibrosis, also known as fibrotic scarring, is a pathological wound healing in which connective tissue replaces normal parenchymal tissue to the extent that it goes unchecked, leading to considerable tissue remodelling and the formation of perma ...
can lead to obstruction of the urinary tract,
hydronephrosis Hydronephrosis describes hydrostatic dilation of the renal pelvis and calyces as a result of obstruction to urine flow downstream. Alternatively, hydroureter describes the dilation of the ureter, and hydronephroureter describes the dilation of th ...
, and
kidney failure Kidney failure, also known as end-stage kidney disease, is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney failure is classified as ei ...
.
Bladder cancer Bladder cancer is any of several types of cancer arising from the tissues of the urinary bladder. Symptoms include blood in the urine, pain with urination, and low back pain. It is caused when epithelial cells that line the bladder become mal ...
diagnosis and mortality are generally elevated in affected areas; efforts to control schistosomiasis in
Egypt Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia via a land bridge formed by the Sinai Peninsula. It is bordered by the Medite ...
have led to decreases in the bladder cancer rate. The risk of bladder cancer appears to be especially high in male smokers, perhaps due to chronic irritation of the bladder lining allowing it to be exposed to
carcinogen A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive substa ...
s from smoking. In women, genitourinary disease can also include genital lesions that may lead to increased rates of HIV transmission. If lesions involve the fallopian tubes or ovaries, it may lead to infertility. If the reproductive organs in male are affected, there could be blood in the sperm. Urinary symptoms may include: * Blood in the urine - blood is usually seen at the end of a urine stream (most common symptom) * Painful urination * Increase frequency of urination * Protein in the urine * Secondary urinary tract infection * Secondary kidney infection Genital symptoms may include: * Inflammation and ulceration of uterine cervix, vagina, or vulva * Blood in the sperm * Infertility in female Kidney function is unaffected in many cases, and the lesions are reversible with proper treatment to eliminate the worms.


Neuroschistosomiasis

Central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all pa ...
lesions occur occasionally due to inflammation and granuloma development around eggs or worms that find their way to the brain or spinal cord through the circulatory system, and they can potentially develop irreversible scarring without proper treatment. Cerebral granulomatous disease may be caused by ''S. japonicum'' eggs in the brain during both the acute and chronic phase of the disease. Communities in China affected by ''S. japonicum'' have rates of
seizures An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or neural oscillation, synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much o ...
eight times higher than baseline. Cerebral granulomatous infection may also be caused by ''S. mansoni''. ''In situ'' egg deposition following the anomalous migration of the adult worm, which appears to be the only mechanism by which ''Schistosoma'' can reach the central nervous system in people with schistosomiasis. The destructive action on the nervous tissue and the mass effect produced by a large number of eggs surrounded by multiple, large granulomas in circumscribed areas of the brain characterize the pseudotumoral form of neuroschistosomiasis and are responsible for the appearance of clinical manifestations: headache, hemiparesis, altered mental status, vertigo, visual abnormalities, seizures, and ataxia. Similarly, granulomatous lesions from ''S. mansoni'' and ''S. haematobium'' eggs in the
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spi ...
can lead to
transverse myelitis Transverse myelitis (TM) is a rare neurological condition wherein the spinal cord is inflamed. The adjective ''transverse'' implies that the spinal inflammation (myelitis) extends horizontally throughout the cross section of the spinal cord; t ...
(inflammation of the spinal cord) with flaccid
paraplegia Paraplegia, or paraparesis, is an impairment in motor or sensory function of the lower extremities. The word comes from Ionic Greek () "half-stricken". It is usually caused by spinal cord injury or a congenital condition that affects the neural ...
. In cases with advanced hepatosplenic and urinary schistosomiasis, the continuous embolization of eggs from the portal mesenteric system (''S. mansoni'') or portal mesenteric-pelvic system (''S. haematobium'') to the brain, results in a sparse distribution of eggs associated with scant periovular inflammatory reaction, usually with little or no clinical significance. Spinal cord inflammation (
transverse myelitis Transverse myelitis (TM) is a rare neurological condition wherein the spinal cord is inflamed. The adjective ''transverse'' implies that the spinal inflammation (myelitis) extends horizontally throughout the cross section of the spinal cord; t ...
) symptoms may include: * Paralysis of the lower extremities * Loss of bowel or urinary control * Loss of sensation below the level of the lesion * Pain below the level of the lesion Cerebral granulomatous infection symptoms may include: * Seizures * Headaches * Motor impairment * Sensory impairment * Cerebellar symptoms ** Unsteady gait ** Inability to stand or sit without support ** Uncoordinated movements ** Scanning speech ** Irregular eye movements Corticosteroids is used to prevent permanent neurological damage from the inflammatory response to the eggs, and sometimes anticonvulsant is needed to stop the seizures. Corticosteroid is given prior to administration of praziquantel.


Transmission and life cycle

Infected ''Schistosoma'' individuals release eggs into water via their fecal material or urine. After
larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. ...
e hatch from these eggs, the larvae infect a very specific type of freshwater snail. For example, in ''S. haematobium'' and ''S. intercalatum'' it is snails of the genus '' Bulinus'', in ''S. mansoni'' it is ''
Biomphalaria ''Biomphalaria'' is a genus of air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the family Planorbidae, the ram's horn snails and their allies.MolluscaBase (2018). Biomphalaria Preston, 1910. Accessed through: World R ...
'', and in ''S. japonicum'' it is '' Oncomelania''. The schistosome larvae undergo the next phase of their lifecycles in these snails, spending their time reproducing and developing. Once this step has been completed, the parasite leaves the snail and enters the water column. The parasite can live in the water for only 48 hours without a mammalian host. Once a host has been found, the worm enters its blood vessels. For several weeks, the worm remains in the vessels, continuing its development into its adult phase. When maturity is reached, mating occurs and eggs are produced. Eggs enter the bladder/intestine and are excreted through urine and feces and the process repeats. If the eggs do not get excreted, they can become engrained in the body tissues and cause a variety of problems such as immune reactions and organ damage. While transmission typically occurs only in countries where the freshwater snails are endemic, a case in Germany was reported where a man got schistosomiasis from an infected snail in his aquarium. Humans encounter larvae of the schistosome parasite when they enter contaminated water while bathing, playing, swimming, washing, fishing, or walking through the water.


Life cycle

# The excretion schistosome eggs in urine or feces depending on species # The hatching of the eggs leading to release of the free-swimming, ciliated larvae called miracidia # Miracidia find and penetrate the snails, which are the intermediate hosts (specific species of snails is dependent on the species of schistosoma) # Within the snails, two successive generations of sporocysts occur # Sporocyts gives rise to the infective free-swimming larvae with forked tails called cercariae, and they leave the snails to enter the water # Cercariae finds the human hosts and penetrate their skin # Upon entrance into the human hosts, cercariae lose their tails and become schistosomulae # The schistosomulae travels to the lungs and heart via the venous circulation # They migrate to the portal venous system of the liver where they mature into the adult form with two separate sexes # The adult male and female are paired together, exits the liver via portal venous system, and travel to the venous systems of the intestines or bladder (species dependent) and produce eggs ## ''S. japonicum'' -
superior mesenteric vein In human anatomy, the superior mesenteric vein (SMV) is a blood vessel that drains blood from the small intestine (jejunum and ileum). Behind the neck of the pancreas, the superior mesenteric vein combines with the splenic vein to form the hepa ...
s (but can also inhabit inferior mesenteric veins) ## ''S. mansoni'' -
inferior mesenteric vein In human anatomy, the inferior mesenteric vein (IMV) is a blood vessel that drains blood from the large intestine. It usually terminates when reaching the splenic vein, which goes on to form the portal vein with the superior mesenteric vein (SMV ...
s (but can also inhabit superior mesenteric veins) ## ''S. haematobium'' - vesicular and pelvic venous plexus of the bladder (occasionally rectal venules) ## ''S. intercalatum'' and ''S. guineensis'' - inferior mesenteric plexus (lower portion of the bowels compared to ''S. mansoni'') Schistosomes can live an average of 3–5 years, and the eggs can survive for more than 30 years after infection.


Other hosts

Schistosomiasis is also a concern of cattle husbandry and
mice A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...
. O-methyl-threonine is weakly effective in mouse schistosomiasis but is not in use.


Pathogenesis

The infectious stage starts when the free-swimming larval form of the schistosome, cercariae, penetrates the human skin using their suckers, proteolytic enzymes, and tail movements; the cercariae transformed into schistosomulae by losing its tail and subsequently travels to the heart and lungs through venous system until it eventually reach the liver where it will mature into the adult form. The diseases caused by the schistomes are characterized into acute schistosomiasis and chronic schistosomiasis, and they can vary dependent on the species of schistosome. Acute infection * Minutes to days after initial infection: ** Cercerial dermatitis (Swimmer's itch) - swimmer's itch is caused by a localized allergic reaction at the sites of skin penetration by the cercariae causing an inflammatory reaction that is characterized by itchy red pimples and blisters. * Few weeks to months after initial infection: ** Acute Schistosomiasis (Katayama's Fever) - the exact pathophysiology of this disease remains unknown. It has been hypothesized to be caused by a systemic immune response due to immune complex formation ( Type III hypersensivity) with the foreign antigens on the migratory schistosomula and the eggs, and the subsequent deposition of these complexes on various tissues leading to activation of an autoimmune response. Acute schistosomiasis caused by ''S. mansoni'' and ''S. haematobium'' generally affect people who have been infected for the first time such as tourists visiting endemic regions. In contrast, cases of acute schistosomiasis caused by ''S. japonicum'' can occur in reinfection to population who reside in endemic regions, and they occur in higher incidences and can have worse prognosis. It was proposed that the large amount of egg antigens released by ''S. japonicum'' interact with antibodies leading to the formation of high volume of immune complexes, which cause enlargement of the lymph tissues. This sequence of events can lead to clinical manifestation of fever, enlargement of spleen and liver due to fibrosis, portal hypertension, and death. Chronic infection The clinical manifestations of chronic infection is mainly caused by immune reaction to the eggs entrapment within tissues resulting in
granuloma A granuloma is an aggregation of macrophages that forms in response to chronic inflammation. This occurs when the immune system attempts to isolate foreign substances that it is otherwise unable to eliminate. Such substances include infectious ...
formation and chronic inflammation. Adult worms live together in pairs (one male and female), sexually reproduce, and lay eggs in the veins around the intestines and bladder depending on the species, and these eggs can rupture the wall of the veins to escape to the surrounding tissues. The eggs make their way through the tissues to the intestinal or bladder lumen with help of proteolytic enzymes, however, a large amount of eggs are unable to finish their journey and remained stuck within the tissues where they can elicit an immune response. The miracidia in these eggs can then release antigens that stimulate an inflammatory immune response. The miracidia within the eggs live for around 6–8 weeks before they die and stop releasing the antigens. The granulomatous response is a cellular immune response mediated by CD4+ T cells, neutrophils, eosinophils, lymphocytes, macrophages, and monocytes, and this chronic inflammatory response elicited by the eggs can cause fibrosis, tissue destruction, and granuloma nodules that disrupt the functions of the organs involved. Th1 helper cell response is prominent releasing cytokines such as IFN-γ during the early phases of infection, and it transitions to Th2 response leading to increase in level of IgE, IL-4, and eosinophils as egg production progresses. In chronic infections, the Th2 response shifts to increasing the level of IL-10, IL-13, and IgG4, which reverses the progression of the granulomas and lead to collagen deposition at the sites of the granulomas. The specific clinical symptoms and severity of the disease this causes depends on the type of schistosome infection, duration of infection, number of eggs, and the organ at which the eggs are deposited. The amount of eggs entrapped in the tissues will continue to increase if the schistosoma are not eliminated.


Diagnosis


Identification of eggs in stools

Diagnosis of infection is confirmed by the identification of eggs in stools. Eggs of ''S. mansoni'' are about 140 by 60 µm in size and have a lateral spine. The diagnosis is improved through the use of the Kato-Katz technique, a semiquantitative stool examination technique. Other methods that can be used are
enzyme-linked immunosorbent assay The enzyme-linked immunosorbent assay (ELISA) (, ) is a commonly used analytical biochemistry assay, first described by Eva Engvall and Peter Perlmann in 1971. The assay uses a solid-phase type of enzyme immunoassay (EIA) to detect the presence ...
, circumoval precipitation test, and alkaline phosphatase immunoassay. Microscopic identification of eggs in stool or urine is the most practical method for diagnosis. Stool examination should be performed when infection with ''S. mansoni'' or ''S. japonicum'' is suspected, and urine examination should be performed if ''S. haematobium'' is suspected. Eggs can be present in the stool in infections with all ''Schistosoma'' species. The examination can be performed on a simple smear (1 to 2 mg of fecal material). Because eggs may be passed intermittently or in small numbers, their detection is enhanced by repeated examinations or concentration procedures, or both. In addition, for field surveys and investigational purposes, the egg output can be quantified by using the Kato-Katz technique (20 to 50 mg of fecal material) or the Ritchie technique. Eggs can be found in the urine in infections with ''S. haematobium'' (recommended time for collection: between noon and 3 PM) and with ''S. japonicum''. Quantification is possible by using filtration through a nucleopore filter membrane of a standard volume of urine followed by egg counts on the membrane. Tissue biopsy (rectal biopsy for all species and biopsy of the bladder for ''S. haematobium'') may demonstrate eggs when stool or urine examinations are negative. Identification of microhematuria in urine using urine reagent strips is more accurate than circulating antigen tests in the identification of active schistosomiasis in endemic areas.


Antibody detection

Antibody detection can be useful to indicate schistosome infection in people who have traveled to areas where schistosomiasis is common and in whom eggs cannot be demonstrated in fecal or urine specimens. Test sensitivity and specificity vary widely among the many tests reported for the serologic diagnosis of schistosomiasis and are dependent on both the type of antigen preparations used (crude, purified, adult worm, egg, cercarial) and the test procedure. At the U.S.
Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georg ...
, a combination of tests with purified adult worm antigens is used for antibody detection. All serum specimens are tested by FAST-ELISA using ''S. mansoni'' adult microsomal antigen. A positive reaction (greater than 9 units/µl serum) indicates infection with ''Schistosoma'' species. Sensitivity for ''S. mansoni'' infection is 99%, 95% for ''S. haematobium'' infection, and less than 50% for ''S. japonicum'' infection. Specificity of this assay for detecting schistosome infection is 99%. Because test sensitivity with the FAST-ELISA is reduced for species other than ''S. mansoni'', immunoblots of the species appropriate to the person's travel history are also tested to ensure detection of ''S. haematobium'' and ''S. japonicum'' infections. Immunoblots with adult worm microsomal antigens are species-specific, so a positive reaction indicates the infecting species. The presence of antibody is indicative only of schistosome infection at some time and cannot be correlated with clinical status, worm burden, egg production, or prognosis. Where a person has traveled can help determine which ''Schistosoma'' species to test for by immunoblot. In 2005, a field evaluation of a novel handheld microscope was undertaken in
Uganda }), is a landlocked country in East Africa. The country is bordered to the east by Kenya, to the north by South Sudan, to the west by the Democratic Republic of the Congo, to the south-west by Rwanda, and to the south by Tanzania. The sou ...
for the diagnosis of intestinal schistosomiasis by a team led by Russell Stothard from the Natural History Museum of London, working with the Schistosomiasis Control Initiative, London.


Molecular diagnostics

Polymerase chain reaction The polymerase chain reaction (PCR) is a method widely used to rapidly make millions to billions of copies (complete or partial) of a specific DNA sample, allowing scientists to take a very small sample of DNA and amplify it (or a part of it) ...
(PCR) based testing is accurate and rapid. However, it is not frequently used in countries where the disease is common due to the cost of the equipment and the technical expertise required to run the tests. Using a microscope to detect eggs costs about US$0.40 per test whereas PCR is about $US 7 per test as of 2019.
Loop-mediated isothermal amplification Loop-mediated isothermal amplification (LAMP) is a single-tube technique for the amplification of DNA and a low-cost alternative to detect certain diseases. Reverse transcription loop-mediated isothermal amplification (RT-LAMP) combines LAMP wit ...
are being studied as they are lower cost. LAMP testing is not commercially available as of 2019.


Laboratory testing

''S. haematobium'' screening in the community can be done by using urine dip-stick to check for hematuria, and the
stool guaiac test The stool guaiac test or guaiac fecal occult blood test (gFOBT) is one of several methods that detects the presence of fecal occult blood (blood invisible in the feces). The test involves placing a fecal sample on guaiac paper (containing a phen ...
can be used to test for blood in the stool for potential ''S. mansoni'' and ''S. japonicum'' infection. For travelers or migrants in endemic regions, complete blood count with differential can be used to identify a high level of eosinophil in the blood, which could be indicative of an acute infection.
Liver function test Liver function tests (LFTs or LFs), also referred to as a hepatic panel, are groups of blood tests that provide information about the state of a patient's liver. These tests include prothrombin time (PT/INR), activated partial thromboplastin ti ...
can be ordered if hepatosplenic schistosomiasis is suspected, and a subsequent hepatitis test panel can be ordered if liver function test is abnormal.


Tissue biopsy

If other diagnostic methods of schistosomiasis have failed to detect the infection, but there is still a high suspicion for schistosomiasis, tissue biopsy from the rectum, bladder, and liver can be obtained to look for schistosome eggs within the tissue samples.


Imaging

Imaging modalities such as
X-rays An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10  picometers to 10 nanometers, corresponding to frequencies in the range 30  ...
,
ultrasound Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies ...
, computed tomography (CT), and magnetic resonance imaging (MRI) can be utilized to evaluate for severity of schistosomiasis and damages of the infected organs. For example, X-ray and CT scans of the chest can be used to detect lesions in the lungs from pulmonary schistosomiasis, and pelvic X-ray can reveal calcification of the bladder in chronic urinary schistosomiasis. Ultrasound may be used to look for abnormalities in the liver and spleen in hepatosplenic schistosomiasis, and CT scan of the liver is a good tool to look for calcification in the liver associated with ''S. japonicum'' infection. CT scan can also be used to assess damages from the schistosomiasis infection in the intestinal, urogenital, and central nervous system. MRI is used to evaluate schistosomiasis of the central nervous system, liver, and genital. PET/CT scan that identifies tissues with higher metabolic activity have been used to help diagnose schistosomiasis in rare cases. This is due to the high level of inflammation caused by the schistosomal eggs, which increases the metabolic rate of the surrounding tissues.


Prevention

Many countries are working towards eradicating the disease. The
World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of ...
is promoting these efforts. In some cases, urbanization, pollution, and the consequent destruction of snail habitat have reduced exposure, with a subsequent decrease in new infections. The elimination of snail populations using molluscicides had been attempted to prevent schistosomiasis in the past, but it was an expensive process that often only reduce but not eliminate the snail population. The drug praziquantel is used for prevention in high-risk populations living in areas where the disease is common. The Centers for Disease Control and Prevention advises avoiding drinking or coming into contact with contaminated water in areas where schistosomiasis is common. A 2014 review found tentative evidence that increasing access to
clean water Drinking water is water that is used in drink or food preparation; potable water is water that is safe to be used as drinking water. The amount of drinking water required to maintain good health varies, and depends on physical activity level, a ...
and
sanitation Sanitation refers to public health conditions related to clean drinking water and treatment and disposal of human excreta and sewage. Preventing human contact with feces is part of sanitation, as is hand washing with soap. Sanitation system ...
reduces schistosome infection. Other important preventive measures include hygiene education leading to behavioral change and sanitary engineering to ensure safe water supply.


Preventive chemotherapy

For schistosomiasis control, World Health Organization recommends preventive chemotherapy, which is treatment of entire affected population and periodic treatment of all groups at high-risk at acquiring schistosomiasis with use of Praziquantel. In 2019, 44.5% of people with schistosomiasis was treated globally, and 67.2% of school-aged children needed preventive chemotherapy received treatment.


Snails, dams, and prawns

For many years from the 1950s onwards, vast dams and irrigation schemes were constructed, causing a massive rise in water-borne infections from schistosomiasis. The detailed specifications laid out in various United Nations documents since the 1950s could have minimized this problem. Irrigation schemes can be designed to make it hard for the snails to colonize the water and to reduce the contact with the local population. Even though guidelines on how to design these schemes to minimise the spread of the disease had been published years before, the designers were unaware of them. The dams appear to have reduced the population of the large migratory prawn ''
Macrobrachium ''Macrobrachium'' is a genus of freshwater prawns or shrimps characterised by the extreme enlargement of the second pair of pereiopods, at least in the male. Species It contains these species: *'' Macrobrachium acanthochirus'' F. Villalobo ...
'', which eats the snails. After the construction of fourteen large dams, greater increases in schistosomiasis occurred in the historical habitats of native prawns than in other areas. Further, at the 1986 Diama Dam on the
Senegal River ,french: Fleuve Sénégal) , name_etymology = , image = Senegal River Saint Louis.jpg , image_size = , image_caption = Fishermen on the bank of the Senegal River estuary at the outskirts of Saint-Louis, Senegal ...
, restoring prawns upstream of the dam reduced both snail density and the human schistosomiasis reinfection rate.


Integrated strategy in China

In China, the national strategy for schistosomiasis control has shifted three times since it was first initiated: transmission control strategy (from mid-1950s to early 1980s), morbidity control strategy (from mid-1980s to 2003), and the "new integrated strategy" (2004 to present). The morbidity control strategy focused on synchronous chemotherapy for humans and bovines and the new strategy developed in 2004 intervenes in the transmission pathway of schistosomiasis, mainly including replacement of bovines with machines, prohibition of grazing cattle in the grasslands, improving sanitation, installation of fecal-matter containers on boats, praziquantel drug therapy, snail control, and health education. A 2018 review found that the "new integrated strategy" was highly effective to reduce the rate of ''S. japonicum'' infection in both humans and the intermediate host snails and reduced the infection risk by 3–4 times relative to the conventional strategy.


Treatment

Two drugs, praziquantel and oxamniquine, are available for the treatment of schistosomiasis. They are considered equivalent in relation to efficacy against ''S. mansoni'' and safety. Because of praziquantel's lower cost per treatment, and oxaminiquine's lack of efficacy against the urogenital form of the disease caused by ''S. haematobium'', in general praziquantel is considered the first option for treatment. Praziquantel can be safely used in pregnant women and young children. The treatment objective is to cure the disease and to prevent the evolution of the acute to the chronic form of the disease. All cases of suspected schistosomiasis should be treated regardless of presentation because the adult parasite can live in the host for years. Schistosomiasis is treatable by taking by mouth a single dose of the drug praziquantel annually. Praziquantel only eliminates the adult schistosomes, but it is not effective in killing the eggs and immature worms. Live eggs can be excreted by the infected individuals for weeks after treatment with praziquantel. The immature worms can survive and grow up to be adult schistosomes after praziquantel therapy. Thus, it is important to have repeated schistosomiasis testing of the stool and/or urine around 4–6 weeks after praziquantel therapy. Treatment of praziquantel may be repeated to ensure complete elimination of the parasite. The WHO has developed guidelines for community treatment based on the impact the disease has on children in villages in which it is common: * When a village reports more than 50 per cent of children have blood in their urine, everyone in the village receives treatment. * When 20 to 50 percent of children have bloody urine, only school-age children are treated. * When fewer than 20 percent of children have symptoms, mass treatment is not implemented. Other possible treatments include a combination of praziquantel with metrifonate,
artesunate Artesunate (AS) is a medication used to treat malaria. The intravenous form is preferred to quinine for severe malaria. Often it is used as part of combination therapy, such as artesunate plus mefloquine. It is not used for the prevention of ma ...
, or
mefloquine Mefloquine, sold under the brand name Lariam among others, is a medication used to prevent or treat malaria. When used for prevention it is typically started before potential exposure and continued for several weeks after potential exposure. It ...
. A
Cochrane review Cochrane (previously known as the Cochrane Collaboration) is a British international charitable organisation formed to organise medical research findings to facilitate evidence-based choices about health interventions involving health profess ...
found tentative evidence that when used alone, metrifonate was as effective as praziquantel. Mefloquine, which has previously been used to treat and prevent malaria, was recognised in 2008–2009 to be effective against schistosomes. Historically,
antimony potassium tartrate Antimony potassium tartrate, also known as potassium antimonyl tartrate, potassium antimontarterate, or tartar emetic, has the formula K2Sb2(C4H2O6)2. The compound has long been known as a powerful emetic, and was used in the treatment of schistoso ...
remained the treatment of choice for schistosomiasis until the development of praziquantel in the 1980s. Post-treatment monitoring
Osteopontin Osteopontin (OPN), also known as bone /sialoprotein I (BSP-1 or BNSP), early T-lymphocyte activation (ETA-1), secreted phosphoprotein 1 (SPP1), 2ar and Rickettsia resistance (Ric), is a protein that in humans is encoded by the ''SPP1'' gene (secr ...
(OPN) is a promising tool for monitoring praziquantel efficacy and post-treatment fibrosis regression as (OPN) expression is modulated by ''S. mansoni'' egg antigens and its levels correlate with severity of schistosomiasis fibrosis and portal hypertension in mice and humans. Praziquantel pharmacotherapy reduces systemic OPN levels and liver collagen content in mice.


Epidemiology

The disease is found in
tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...
countries in Africa, the
Caribbean The Caribbean (, ) ( es, El Caribe; french: la Caraïbe; ht, Karayib; nl, De Caraïben) is a region of the Americas that consists of the Caribbean Sea, its islands (some surrounded by the Caribbean Sea and some bordering both the Caribbean S ...
, eastern South America,
Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical south-eastern region of Asia, consisting of the regions that are situated south of mainland ...
, and the
Middle East The Middle East ( ar, الشرق الأوسط, ISO 233: ) is a geopolitical region commonly encompassing Arabia (including the Arabian Peninsula and Bahrain), Asia Minor (Asian part of Turkey except Hatay Province), East Thrace (Europ ...
. ''S. mansoni'' is found in parts of South America and the Caribbean, Africa, and the Middle East; ''S. haematobium'' in Africa and the Middle East; and ''S. japonicum'' in the
Far East The ''Far East'' was a European term to refer to the geographical regions that includes East and Southeast Asia as well as the Russian Far East to a lesser extent. South Asia is sometimes also included for economic and cultural reasons. The ...
. ''S. mekongi'' and ''S. intercalatum'' are found locally in
Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical south-eastern region of Asia, consisting of the regions that are situated south of mainland ...
and central
West Africa West Africa or Western Africa is the westernmost region of Africa. The United Nations defines Western Africa as the 16 countries of Benin, Burkina Faso, Cape Verde, The Gambia, Ghana, Guinea, Guinea-Bissau, Ivory Coast, Liberia, Mali ...
, respectively. The disease is
endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...
in about 75 developing countries and mainly affects people living in rural agricultural and peri-urban areas.


Infection estimates

In 2010, approximately 238 million people were infected with schistosomiasis, 85 percent of whom live in Africa. An earlier estimate from 2006 had put the figure at 200 million people infected. As of the latest WHO record, 236.6 million people were infected in 2019. In many of the affected areas, schistosomiasis infects a large proportion of children under 14 years of age. An estimated 600 to 700 million people worldwide are at risk from the disease because they live in countries where the organism is common. In 2012, 249 million people were in need of treatment to prevent the disease. This likely makes it the most common parasitic infection with malaria second and causing about 207 million cases in 2013. ''S. haematobium'', the infectious agent responsible for urogenital schistosomiasis, infects over 112 million people annually in Sub-Saharan Africa alone.Luke F. Pennington and Michael H. Hsieh (2014
Immune Response to Parasitic Infections
, Bentham e books, Vol 2, pp. 93-124,
It is responsible for 32 million cases of
dysuria Dysuria refers to painful or uncomfortable urination. It is one of a constellation of ''irritative'' bladder symptoms (also sometimes referred to as lower urinary tract symptoms), which includes nocturia and urinary frequency. Diagnosis The cl ...
, 10 million cases of
hydronephrosis Hydronephrosis describes hydrostatic dilation of the renal pelvis and calyces as a result of obstruction to urine flow downstream. Alternatively, hydroureter describes the dilation of the ureter, and hydronephroureter describes the dilation of th ...
, and 150,000 deaths from
kidney failure Kidney failure, also known as end-stage kidney disease, is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney failure is classified as ei ...
annually, making ''S. haematobium'' the world's deadliest schistosome.


Deaths

Estimates regarding the number of deaths vary. Worldwide, the
Global Burden of Disease Study The Global Burden of Disease Study (GBD) is a comprehensive regional and global research program of disease burden that assesses mortality and disability from major diseases, injuries, and risk factors. GBD is a collaboration of over 3600 researc ...
issued in 2010 estimated 12,000 direct deaths while the WHO in 2014 estimated more than 200,000 annual deaths related to schistosomiasis. Another 20 million have severe consequences from the disease. It is the most deadly of the neglected tropical diseases.


History

The most ancient evidence of schistosomiasis dates back to more than 6000 years ago. Studies conducted on human skeletal remains found in northern Syria (5800–4000 BC), demonstrated the evidence of a terminal spined schistosome from the pelvic sediment of skeletal remains. Even if these evidence comes from Syria, it has been suggested that the 'cradle' of schistosomes lies in the region of
African Great Lakes The African Great Lakes ( sw, Maziwa Makuu; rw, Ibiyaga bigari) are a series of lakes constituting the part of the Rift Valley lakes in and around the East African Rift. They include Lake Victoria, the second-largest fresh water lake in the wo ...
, an area in which both the parasites and their intermediate hosts are in an active state of evolution. Subsequently, it is believed that schistosomiasis have spread to Egypt as a result of the importation of monkeys and slaves during reign of the fifth dynasty of Pharaohs (~ 2494–2345 BC). Schistosomiasis is known as bilharzia or bilharziosis in many countries, after German physician
Theodor Bilharz Theodor Maximilian Bilharz (23 March 1825 – 9 May 1862) was a German physician who made pioneering discoveries in the field of parasitology. His contributions led to the foundation of tropical medicine. He is best remembered as the discoverer ...
, who first described the cause of urinary schistosomiasis in 1851. The first physician who described the entire disease cycle was the Brazilian parasitologist Pirajá da Silva in 1908. The earliest known case of infection was discovered in 2014, belonging to a child who lived 6,200 years ago. It was a common cause of death for Egyptians in the Greco-Roman Period. In 2016 more than 200 million people needed treatment but only 88 million people were actually treated for schistosomiasis.


Etymology

Schistosomiasis is named for the genus of parasitic flatworm ''Schistosoma'', whose name means 'split body'. The name Bilharzia comes from
Theodor Bilharz Theodor Maximilian Bilharz (23 March 1825 – 9 May 1862) was a German physician who made pioneering discoveries in the field of parasitology. His contributions led to the foundation of tropical medicine. He is best remembered as the discoverer ...
, a German
pathologist Pathology is the study of the causes and effects of disease or injury. The word ''pathology'' also refers to the study of disease in general, incorporating a wide range of biology research fields and medical practices. However, when used in ...
working in
Egypt Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia via a land bridge formed by the Sinai Peninsula. It is bordered by the Medite ...
in 1851 who first discovered these worms.


Society and culture

Schistosomiasis is endemic in Egypt, exacerbated by the country's dam and irrigation projects along the
Nile The Nile, , Bohairic , lg, Kiira , Nobiin: Áman Dawū is a major north-flowing river in northeastern Africa. It flows into the Mediterranean Sea. The Nile is the longest river in Africa and has historically been considered the longest ...
. From the late 1950s through the early 1980s, infected villagers were treated with repeated injections of
tartar emetic Antimony potassium tartrate, also known as potassium antimonyl tartrate, potassium antimontarterate, or tartar emetic, has the formula K2Sb2(C4H2O6)2. The compound has long been known as a powerful emetic, and was used in the treatment of schistoso ...
. Epidemiological evidence suggests that this campaign unintentionally contributed to the spread of
hepatitis C Hepatitis C is an infectious disease caused by the hepatitis C virus (HCV) that primarily affects the liver; it is a type of viral hepatitis. During the initial infection people often have mild or no symptoms. Occasionally a fever, dark urine, ...
via unclean needles. Egypt has the world's highest hepatitis C infection rate, and the infection rates in various regions of the country closely track the timing and intensity of the anti-schistosomiasis campaign. From ancient times to the early 20th century, schistosomiasis' symptom of blood in the urine was seen as a male version of menstruation in Egypt and was thus viewed as a
rite of passage A rite of passage is a ceremony or ritual of the passage which occurs when an individual leaves one group to enter another. It involves a significant change of status in society. In cultural anthropology the term is the Anglicisation of ''rite ...
for boys. Among human parasitic diseases, schistosomiasis ranks second behind malaria in terms of socio-economic and public health importance in tropical and subtropical areas.


Research

A proposed vaccine against ''S. haematobium'' infection called "Bilhvax" underwent a phase 3 clinical trial among children in Senegal. The results, reported in 2018, showed that it was not effective despite provoking some immune response. Using CRISPR gene editing technology, researchers decreased the symptoms due to schistosomiasis in an animal model.


See also

* Angiostrongyliasis, another disease transmitted by snails


References


External links

*
''River of Hope''
— documentary about the rise of schistosomiasis along the Senegal river (video, 47 mins)
Schistosomiasis information for travellers from IAMAT
( International Association for Medical Assistance to Travellers) * by Facts in Motion {{Diseases of Poverty, state=collapsed Waterborne diseases Helminthiases Zoonoses Tropical diseases Hepatology Infectious causes of cancer Wikipedia medicine articles ready to translate Wikipedia infectious disease articles ready to translate