Capillaria hepatica
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''Capillaria hepatica'' is a parasitic nematode which causes
hepatic capillariasis 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 is ...
in rodents and numerous other mammal species, including humans. The life cycle of ''C. hepatica'' may be completed in a single host species. However, the eggs, which are laid in the liver, must mature outside of the host body (in the environment) prior to infecting a new host. So the death of the host in which the adults reach sexual maturity, either by being eaten or dying and decomposing, is necessary for completion of the life cycle.


Discovery and taxonomy

This species was first described in 1893, from specimens found in the liver of ''Rattus norvegicus'', and named ''Trichocephalus hepaticus''. Various authors have subsequently renamed it ''Trichosoma hepaticum'', ''Capillaria hepatica'', ''Hepaticola hepatica'' and ''Calodium hepaticum''. Currently it is usually referred to as either ''Capillaria hepatica'' or, less often, ''Calodium hepaticum''.


Hosts and distribution

Adults are often found in dozens of rodent species, but also occur in a wide variety of other wild and domestic mammals, and occasionally humans. ''C. hepatica'' has been found in temperate and tropical zones on every continent and infestation rates of wild-caught rats of up to 100% have been reported. Usually, ''Capillaria hepatica'' is found in rodents, monkeys and other animals. ''Capillaria hepatica'' is rarely found in humans and at least 40 cases have been reported. There are no endemic areas of infection with ''C. hepatica'' and human infection primarily results from
Zoonotic A zoonosis (; plural zoonoses) or zoonotic disease is an infectious disease of humans caused by a pathogen (an infectious agent, such as a bacterium, virus, parasite or prion) that has jumped from a non-human (usually a vertebrate) to a human. ...
transmission. Of the human infections, most have been found in children under the age of 5.


Tissue niche and morphology

The tissue
niche Niche may refer to: Science *Developmental niche, a concept for understanding the cultural context of child development *Ecological niche, a term describing the relational position of an organism's species *Niche differentiation, in ecology, the ...
of this parasite is the liver. The adult females will deposit eggs in the
parenchyma Parenchyma () is the bulk of functional substance in an animal organ or structure such as a tumour. In zoology it is the name for the tissue that fills the interior of flatworms. Etymology The term ''parenchyma'' is New Latin from the word π ...
of the liver. Occasionally in humans larvae will migrate to the lungs, kidneys and other organs. Adult worms take the shape of a slender nematode, with the anterior part of the body narrow and the posterior part gradually swelling. The females measure about 53–78mm x 0.11–0.20mm, but the males are approximately 24–37mm x 0.07–0.10mm. The adult worms are rarely seen intact, as they mature and die in the
parenchyma Parenchyma () is the bulk of functional substance in an animal organ or structure such as a tumour. In zoology it is the name for the tissue that fills the interior of flatworms. Etymology The term ''parenchyma'' is New Latin from the word π ...
of the liver. The adult females lay eggs that are about 48-66μm x 28-36μm. The shell of the eggs is striated with shallow polar prominences at either end. Numerous mini-pores can be seen in the outer shell as well. Un
embryonated Embryonated, unembryonated and de-embryonated are terms generally used in reference to eggs or, in botany, to seeds. The words are often used as professional jargon rather than as universally applicable terms or concepts. Examples of relevant fields ...
eggs may be ingested by a carnivore, in which case they are harmless and pass out in the feces. Eggs will embryonate in the environment, where they require air and damp soil to become infective. Under optimal conditions this takes about 30 days. Larvae are juvenile versions of the adult worm.


Life cycle

Hosts ingest ''C. hepatica'' eggs (from sources outlined below) which hatch into first stage larvae (L1). The L1 larvae bore through the intestinal wall and are carried to the liver by the
hepatic portal vein The portal vein or hepatic portal vein (HPV) is a blood vessel that carries blood from the gastrointestinal tract, gallbladder, pancreas and spleen to the liver. This blood contains nutrients and toxins extracted from digested contents. Approxima ...
. Development from the L1 stage to sexually mature adults occurs in the liver within 18–21 days. Eggs are laid in the liver
parenchyma Parenchyma () is the bulk of functional substance in an animal organ or structure such as a tumour. In zoology it is the name for the tissue that fills the interior of flatworms. Etymology The term ''parenchyma'' is New Latin from the word π ...
of the host throughout the adult worm's life span, which lasts for about 30–40 days. Up to 938,000 eggs have been reported from the liver of a single rodent host. The eggs in the liver exist in a state of arrested developmentthey are unable to develop into larvae until they spend some time outside of the host, in the environment. Escaping from the liver tissue may be accomplished either by the death and decomposition of the host's body, or by the consumption and digestion of the host by a
predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
or
scavenger Scavengers are animals that consume dead organisms that have died from causes other than predation or have been killed by other predators. While scavenging generally refers to carnivores feeding on carrion, it is also a herbivorous feeding b ...
. If the host is eaten, the eggs will pass into the environment in the feces of the predator or scavenger. In the environment, eggs require 4–5 weeks to develop, and may remain viable in a dormant state for several more months. Once these "environmentally-conditioned" eggs are eaten by a suitable host, the first stage larvae (L1) hatch in the intestine and continue the life cycle. Humans are usually infected after ingesting embryonated eggs in fecal-contaminated food, water, or soil.


Pathogenesis and survival in host

In humans ''C. hepatica'' causes
Hepatic capillariasis 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 is ...
, a serious liver disorder. The
Nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-Parasitism, parasitic nematodes also known as eelworms. They are a diverse animal phylum inhab ...
wanders through the host liver causing loss of liver cells and thereby loss of function. However, as the adult ''C. hepatica'' begin to die in the liver tissue, their decomposition accelerates the immune response of the host. This response leads to chronic
inflammation Inflammation (from la, wikt:en:inflammatio#Latin, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or Irritation, irritants, and is a protective response involving im ...
and Encapsulation of the dead worms in
collagen Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole ...
fibers, and eventually to septal
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 ...
(abnormal connective tissue growth) and
cirrhosis Cirrhosis, also known as liver cirrhosis or hepatic cirrhosis, and end-stage liver disease, is the impaired liver function caused by the formation of scar tissue known as fibrosis due to damage caused by liver disease. Damage causes tissue repai ...
of the liver. This leaves the eggs behind and they can become encased by Granulomatous tissue, with large sections of the
Parenchyma Parenchyma () is the bulk of functional substance in an animal organ or structure such as a tumour. In zoology it is the name for the tissue that fills the interior of flatworms. Etymology The term ''parenchyma'' is New Latin from the word π ...
becoming replaced by these egg masses. ''Capillaria hepatica'' can also cause
Hepatomegaly Hepatomegaly is the condition of having an enlarged liver. It is a non-specific medical sign having many causes, which can broadly be broken down into infection, hepatic tumours, or metabolic disorder. Often, hepatomegaly will present as an abdomi ...
. Infections of C. hepatica can present with several clinical symptoms including, abdominal pain in the liver area, weight loss, decreased appetite, fever and chills,
hepatitis Hepatitis is inflammation of the liver tissue. Some people or animals with hepatitis have no symptoms, whereas others develop yellow discoloration of the skin and whites of the eyes (jaundice), poor appetite, vomiting, tiredness, abdominal pa ...
(liver inflammation),
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 ...
(excess fluid in the peritoneal cavity) and
hepatolithiasis Hepatolithiasis is the presence of gallstones in the biliary ducts of the liver. Treatment is usually surgical. It is rare in Western countries, but prevalent in East Asia.* The gallstones are normally found proximal to the left and right hepatic ...
(gallstones in the bile ducts). This parasite can be fatal in humans, as transmission and survival of the parasite depend on death of the
Definitive host In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' (symbiont). The guest is typically provided with nourishment and shelter. Examples include a ...
in order for the eggs to reach soil and water to embryonate.


Diagnosis and treatment

Diagnosis is made by finding eggs or adults of ''C. hepatica'' in liver tissue from biopsy or
Necropsy An autopsy (post-mortem examination, obduction, necropsy, or autopsia cadaverum) is a surgical procedure that consists of a thorough examination of a corpse by dissection to determine the cause, mode, and manner of death or to evaluate any di ...
samples. The encapsulated eggs and adults may appear as white nodules which measure 2–3mm in diameter on the surface and interior of the liver at
autopsy An autopsy (post-mortem examination, obduction, necropsy, or autopsia cadaverum) is a surgical procedure that consists of a thorough examination of a corpse by dissection to determine the cause, mode, and manner of death or to evaluate any di ...
. Key identification features of this parasite are a striated shell and shallow polar prominences of the egg and a narrowing at anterior end and gradual swelling at posterior end of the adult worm. Identification of C. hepatica eggs in the stool does not result from infection of the human host, but from ingestion by that host of livers from infected animals, the eggs will then pass out harmlessly in the feces. Most cases have been determined after death because clinical symptoms resemble those of numerous liver disorders. Successful treatment of human cases with
thiabendazole Tiabendazole (INN, BAN), also known as thiabendazole (AAN, USAN) or TBZ and the trade names Mintezol, Tresaderm, and Arbotect, is a preservative, an antifungal agent, and an antiparasitic agent. Uses Preservative Tiabendazole is used primar ...
or
albendazole Albendazole (also known as albendazolum) is a broad-spectrum anthelmintic and antiprotozoal agent of the benzimidazole type. It is used for the treatment of a variety of intestinal parasite infections, including ascariasis, pinworm infection, h ...
(with or without
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 involv ...
s) have been reported. Albendazole must be taken with food because a fatty meal will increase the
Bioavailability In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation. By definition, when a medication is administered intravenously, its bioavailability is 100%. H ...
of the drug. Two ways of preventing ''C. hepatica'' infections in humans would be to institute effective rodent control programs and preventing dogs and cats from eating rodents.


Paleoparasitology

The first paleoparasitological record of human hepatic capillariasis was published in 2014. Two
calcified Calcification is the accumulation of calcium salts in a body tissue. It normally occurs in the formation of bone, but calcium can be deposited abnormally in soft tissue,Miller, J. D. Cardiovascular calcification: Orbicular origins. ''Nature Mat ...
objects recovered from a 3rd to 4th-century grave of an adolescent in
Amiens Amiens (English: or ; ; pcd, Anmien, or ) is a city and commune in northern France, located north of Paris and south-west of Lille. It is the capital of the Somme department in the region of Hauts-de-France. In 2021, the population of ...
(Northern
France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...
) were identified as probable
hydatid cyst Echinococcosis is a parasitic disease of tapeworms of the ''Echinococcus'' type. The two main types of the disease are ''cystic echinococcosis'' and ''alveolar echinococcosis''. Less common forms include ''polycystic echinococcosis'' and ''unic ...
s. By using thin-section
petrographic Petrography is a branch of petrology that focuses on detailed descriptions of rocks. Someone who studies petrography is called a petrographer. The mineral content and the textural relationships within the rock are described in detail. The class ...
techniques, probable ''Capillaria hepatica'' eggs were identified in the wall of the
cyst A cyst is a closed sac, having a distinct envelope and cell division, division compared with the nearby Biological tissue, tissue. Hence, it is a cluster of Cell (biology), cells that have grouped together to form a sac (like the manner in which ...
s. The authors claimed that
hepatic capillariasis 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 is ...
could be expected given the poor level of environmental
hygiene Hygiene is a series of practices performed to preserve health. According to the World Health Organization (WHO), "Hygiene refers to conditions and practices that help to maintain health and prevent the spread of diseases." Personal hygiene refer ...
prevalent in this period. Identification of tissue-dwelling parasites such as ''C. hepatica'' in
archaeological Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landscap ...
remains is particularly dependent on preservation conditions and
taphonomic Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientist Ivan Efremov t ...
changes and should be interpreted with caution due to morphological similarities with ''
Trichuris ''Trichuris'', often referred to as whipworms (which typically refers to ''T. trichiura'' only in medicine, and to any other species in veterinary medicine), is a genus of parasitic worms from the roundworm family Trichuridae, which are helmint ...
'' sp. eggs.


Research uses

The selective liver damage by ''C. hepatica'' in rodents has been used in model systems to study the extensive regeneration capabilities of the mammalian liver, and for testing
antifibrotic 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 perman ...
drugs. ''C. hepatica'' has attracted interest for use in
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
as a
biocontrol Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also invo ...
of the house mouse, ''
Mus musculus Mus or MUS may refer to: Abbreviations * MUS, the NATO country code for Mauritius * MUS, the IATA airport code for Minami Torishima Airport * MUS, abbreviation for the Centre for Modern Urban Studies on Campus The Hague, Leiden University, Neth ...
''. It has been moderately successful in
Southern Australia The term Southern Australia is generally considered to refer to the states and territories of Australia of New South Wales, Victoria, Tasmania, the Australian Capital Territory and South Australia. The part of Western Australia south of lati ...
.


References


Further reading

* http://indianpediatrics.net/oct2007/781.pdf
DOI.org
''Indian Journal of Pediatrics'', publisher Dr. K C Chaudhuri Foundation, co-published by Springer India * {{DEFAULTSORT:Capillaria Hepatica Parasitic nematodes of mammals Veterinary helminthology Enoplia Zoonoses Nematodes described in 1893 Parasites of rodents