Blastomycosis
   HOME

TheInfoList



OR:

Blastomycosis or blasto is a
fungal infection Fungal infection, also known as mycosis, is disease caused by fungi. Different types are traditionally divided according to the part of the body affected; superficial, subcutaneous, and systemic. Superficial fungal infections include common ti ...
caused by inhaling spores of a ''Blastomyces'' fungus. Only about half of people with the disease have symptoms, which can include
fever Fever, also referred to as pyrexia, is defined as having a body temperature, temperature above the human body temperature, normal range due to an increase in the body's temperature Human body temperature#Fever, set point. There is not a single ...
,
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 pha ...
,
night sweats Night sweats, also referred to as nocturnal hyperhidrosis (Hyperhidrosis - a medical term for excessive sweating + nocturnal - night), is the repeated occurrence of excessive sweating during sleep. The person may or may not also perspire exces ...
,
muscle pains Myalgia (also called muscle pain and muscle ache in layman's terms) is the medical term for muscle pain. Myalgia is a symptom of many diseases. The most common cause of acute myalgia is the overuse of a muscle or group of muscles; another likel ...
, weight loss, chest pain, and feeling tired. Symptoms usually develop between three weeks and three months after breathing in the spores. Most blastomycosis infections affect the lungs. In 25 to 40% of cases, the infection also spreads to other parts of the body, such as the skin, bones or
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 par ...
. Although blastomycosis is especially dangerous for those with weak immune systems, most people diagnosed with blastomycosis have healthy immune systems. ''Blastomyces dermatitidis'' is found in the soil and decaying organic matter like wood or leaves. Outdoor activities like hunting or camping in wooded areas increase the risk of developing blastomycosis. There is no vaccine, but the risk of the disease can be reduced by not disturbing the soil. Treatment is typically with an azole drug such as
itraconazole Itraconazole, sometimes abbreviated ITZ, is an antifungal medication used to treat a number of fungal infections. This includes aspergillosis, blastomycosis, coccidioidomycosis, histoplasmosis, and paracoccidioidomycosis. It may be given by mouth ...
for mild or moderate disease. In severe cases, patients are treated with
amphotericin B Amphotericin B is an antifungal medication used for serious fungal infections and leishmaniasis. The fungal infections it is used to treat include mucormycosis, aspergillosis, blastomycosis, candidiasis, coccidioidomycosis, and cryptococcosis. Fo ...
before azole treatment. In either event, the azole treatment lasts for 6–12 months. Overall, 4-6% of people who develop blastomycosis die; however, if the central nervous system is involved, this rises to 18%. People with
AIDS Human immunodeficiency virus infection and acquired immunodeficiency syndrome (HIV/AIDS) is a spectrum of conditions caused by infection with the human immunodeficiency virus (HIV), a retrovirus. Following initial infection an individual m ...
or on medications that suppress the immune system have the highest risk of death at 25-40%. Blastomycosis 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 elsew ...
to the eastern United States and Canada, especially the Ohio and Mississippi River valleys, the Great Lakes, and the St. Lawrence River valley. In these areas, there are about 1 to 2 cases per 100,000 per year. Less frequently, blastomycosis also occurs in Africa, the Middle East, India, and western North America. Blastomycosis also affects a broad range of non-human mammals, and dogs in particular are an order of magnitude more likely to contract the disease than humans. The ecological niche of ''Blastomyces'' in the wild is poorly understood, and it is unknown if there are any significant host animals. Blastomycosis has existed for millions of years but was first described by Thomas Caspar Gilchrist in 1894. Because of this, it is sometimes called "Gilchrist's disease".


Signs and symptoms

The symptoms of blastomycosis cover a wide range, overlapping with more common conditions; for this reason, blastomycosis has often been called "the great pretender". Many cases are
asymptomatic In medicine, any disease is classified asymptomatic if a patient tests as carrier for a disease or infection but experiences no symptoms. Whenever a medical condition fails to show noticeable symptoms after a diagnosis it might be considered asy ...
or subclinical. Lung symptoms are common, because the lungs are infected in 79% of blastomycosis cases. However, in 25-40% of cases the disease also disseminates to other organs, including the skin. The extent and severity of symptoms depends in part on a person's immune status; less than 50% of healthy people with blastomycosis have symptoms, while immunocompromised patients are especially likely to have the disease spread beyond the lungs to other organs like the skin and bones. Blastomycosis manifests as a primary
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 of t ...
infection in about 79% of cases. The onset is relatively slow and symptoms are suggestive of bacterial pneumonia, often leading to initial treatment with antibacterials. Because the symptoms are variable and nonspecific, blastomycosis is often not even considered in
differential diagnosis In healthcare, a differential diagnosis (abbreviated DDx) is a method of analysis of a patient's history and physical examination to arrive at the correct diagnosis. It involves distinguishing a particular disease or condition from others that p ...
until antibacterial treatment has failed, unless there are known risk factors or skin lesions. The disease may be misdiagnosed as a carcinoma, leading in some cases to surgical removal of the affected tissue. Upper lung lobes are involved somewhat more frequently than lower lobes. If untreated, many cases progress over a period of months to years to become disseminated blastomycosis. Blastomycosis in the lungs may present a variety of symptoms, or no symptoms at all. If symptoms are present they may range from mild
pneumonia Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severity ...
resembling a
pneumococcal ''Streptococcus pneumoniae'', or pneumococcus, is a Gram-positive, spherical bacteria, alpha-hemolytic (under aerobic conditions) or beta-hemolytic (under anaerobic conditions), aerotolerant anaerobic member of the genus Streptococcus. They are ...
infection to acute respiratory distress syndrome (ARDS). Common symptoms include fever, chills, headache, coughing, difficulty breathing, chest pain, and malaise. Without treatment, cases may progress to chronic pneumonia or ARDS. ARDS is an uncommon but dangerous manifestation of blastomycosis. It was seen in 9 of 72 blastomycosis cases studied in northeast Tennessee. Such cases may follow massive exposure, such during brush clearing operations. In the Tennessee study, the fatality rate was 89% in the ARDS cases, but only 10% in the non-ARDS cases. In disseminated blastomycosis, the large Blastomyces yeast cells translocate from the lungs and are trapped in capillary beds elsewhere in the body, where they cause lesions. The skin is the most common organ affected, being the site of lesions in approximately 60% of cases. The signature image of blastomycosis in textbooks is the indolent, verrucous or ulcerated dermal lesion seen in disseminated disease.
Osteomyelitis Osteomyelitis (OM) is an infection of bone. Symptoms may include pain in a specific bone with overlying redness, fever, and weakness. The long bones of the arms and legs are most commonly involved in children e.g. the femur and humerus, while the ...
is also common (12–60% of cases). Other recurring sites of dissemination are the genitourinary tract (kidney, prostate, epididymis; collectively ca. 25% of cases) and the brain (3–10% of cases). 40% of immunocompromised individuals have CNS involvement and present as
brain abscess Brain abscess (or cerebral abscess) is an abscess caused by inflammation and collection of infected material, coming from local (ear infection, dental abscess, infection of paranasal sinuses, infection of the mastoid air cells of the temporal bone ...
, epidural abscess or
meningitis Meningitis is acute or chronic inflammation of the protective membranes covering the brain and spinal cord, collectively called the meninges. The most common symptoms are fever, headache, and neck stiffness. Other symptoms include confusion or ...
. Blastomycosis in non-lung organs such as the skin may present a very wide range of symptoms, including the following: * skin lesions, which may be verrucous (wart-like) or ulcerated with small pustules at the margins. * bone or joint pain due to bone lytic lesions. * pain when urinating due to
prostatitis Prostatitis is an umbrella term for a variety of medical conditions that incorporate bacterial and non-bacterial origin illnesses in the pelvic region. In contrast with the plain meaning of the word (which means "inflammation of the prostate"), the ...
. * hoarseness due to laryngeal involvement. * headache, confusion or other neurological symptoms caused by
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 par ...
involvement.


Cause

Blastomycosis is caused by
dimorphic fungi Dimorphic fungi are fungi that can exist in the form of both mold and yeast. This is usually brought about by change in temperature and the fungi are also described as thermally dimorphic fungi. An example is ''Talaromyces marneffei'', a human ...
in the genus ''Blastomyces'', in the phylum
Ascomycota Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The def ...
and family
Ajellomycetaceae The Ajellomycetaceae are a family of fungi in the Ascomycota, class Eurotiomycetes. The family contains eight genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as vi ...
. In eastern North America, the most common cause of blastomycosis is ''
Blastomyces dermatitidis ''Blastomyces dermatitidis'' is a dimorphic fungus that causes blastomycosis, an invasive and often serious fungal infection found occasionally in humans and other animals. It lives in soil and wet, decaying wood, often in an area close to a wate ...
'', but '' Blastomyces gilchristii'' has been associated with some outbreaks. In western North America, many cases of blastomycosis are caused by '' Blastomyces helicus'', which most commonly attacks immunodeficient people and domestic animals. The species ''
Blastomyces percursus ''Chrysosporium'' is a genus of hyaline hyphomycetes fungi in the family Onygenaceae. ''Chrysosporium'' colonies are moderately fast-growing, flat, white to tan to beige in color; they often have a powdery or granular surface texture. Hyaline, o ...
'' causes many cases of blastomycosis in Africa and the Middle East. In Africa, blastomycosis may also be caused by ''
Blastomyces emzantsi ''Chrysosporium'' is a genus of hyaline hyphomycetes fungi in the family Onygenaceae. ''Chrysosporium'' colonies are moderately fast-growing, flat, white to tan to beige in color; they often have a powdery or granular surface texture. Hyaline, o ...
'', which is often associated with infections outside the lungs. In endemic areas, ''Blastomyces dermatitidis'' lives in soil and rotten wood near lakes and rivers. Although it has never been directly observed growing in nature, it is thought to grow there as a cottony white mold, similar to the growth seen in artificial culture at 25 °C. The moist, acidic soil in the surrounding woodland harbors the fungus.


Pathogenesis

Inhaled conidia of ''Blastomyces'' are
phagocytosed Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis is ca ...
by neutrophils and macrophages in alveoli. Some of these escape phagocytosis and transform into yeast phase rapidly. Having thick walls, these are resistant to phagocytosis. Once they have transitioned to the yeast phase, the ''Blastomyces'' cells express the protein ''BAD-1'', which helps the yeast cells attach to host cells, and also impairs activation of immune cells while inhibiting release of
tumor necrosis factor Tumor necrosis factor (TNF, cachexin, or cachectin; formerly known as tumor necrosis factor alpha or TNF-α) is an adipokine and a cytokine. TNF is a member of the TNF superfamily, which consists of various transmembrane proteins with a homolog ...
. In lung tissue, the cells multiply and may also disseminate through blood and
lymphatics The lymphatic vessels (or lymph vessels or lymphatics) are thin-walled vessels (tubes), structured like blood vessels, that carry lymph. As part of the lymphatic system, lymph vessels are complementary to the cardiovascular system. Lymph vessel ...
to other organs, including the skin, bone, genitourinary tract, and brain. The incubation period for pulmonary blastomycosis is 3 to 15 weeks, although 30–50% of infections are asymptomatic.


Diagnosis

Because the symptoms of blastomycosis resemble those of many other conditions, including
tuberculosis Tuberculosis (TB) is an infectious disease usually caused by '' Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can also affect other parts of the body. Most infections show no symptoms, in ...
and lung cancer, diagnosis is often delayed. In 40% of cases, the diagnosis takes more than a month. A rapid diagnosis can however be made based on microscopic examination of
sputum Sputum is mucus that is coughed up from the lower airways (the trachea and bronchi). In medicine, sputum samples are usually used for a naked eye examination, microbiological investigation of respiratory infections and cytological investigations ...
samples or samples obtained from a tissue
biopsy A biopsy is a medical test commonly performed by a surgeon, interventional radiologist, or an interventional cardiologist. The process involves extraction of sample cells or tissues for examination to determine the presence or extent of a diseas ...
or
bronchoalveolar lavage Bronchoalveolar lavage (BAL) (also known as bronchoalveolar washing) is a diagnostic method of the lower respiratory system in which a bronchoscope is passed through the mouth or nose into an appropriate airway in the lungs, with a measured amoun ...
. Once suspected, the diagnosis of blastomycosis can usually be confirmed by demonstration of the characteristic broad based budding organisms in sputum or tissues by KOH prep, cytology, or histology. Tissue biopsy of skin or other organs may be required in order to diagnose extra-pulmonary disease. Blastomycosis is histologically associated with granulomatous nodules. Commercially available urine antigen testing appears to be quite sensitive in suggesting the diagnosis in cases where the organism is not readily detected. However, commercial antigen tests have a high degree of
cross-reactivity Cross-reactivity, in a general sense, is the reactivity of an observed agent which initiates reactions outside the main reaction expected. This has implications for any kind of test or assay, including diagnostic tests in medicine, and can be a ...
with other endemic fungal conditions such as
histoplasmosis Histoplasmosis is a fungal infection caused by ''Histoplasma capsulatum''. Symptoms of this infection vary greatly, but the disease affects primarily the lungs. Occasionally, other organs are affected; called disseminated histoplasmosis, it can ...
, and thus cannot distinguish blastomycosis from other similar conditions. This cross-reactivity is caused by these related fungal organisms using similar
galactomannan Galactomannans are polysaccharides consisting of a mannose backbone with galactose side groups, more specifically, a (1-4)-linked beta-D-mannopyranose backbone with branchpoints from their 6-positions linked to alpha-D-galactose, (i.e. 1-6-linked ...
s in the
cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mech ...
. While culture of the ''Blastomyces'' organism remains the definitive diagnostic standard, its slow growing nature can lead to a delay of up to four weeks. In addition, sometimes blood and sputum cultures may not detect blastomycosis. Cultures of the
cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissue that surrounds the brain and spinal cord of all vertebrates. CSF is produced by specialised ependymal cells in the choroid plexus of the ventricles of the bra ...
also have poor sensitivity compared to
histopathological Histopathology (compound of three Greek words: ''histos'' "tissue", πάθος ''pathos'' "suffering", and -λογία ''-logia'' "study of") refers to the microscopic examination of tissue in order to study the manifestations of disease. Spec ...
examination of the affected tissue.


Treatment

Under
Infectious Disease Society of America The Infectious Diseases Society of America (IDSA) is a medical association representing physicians, scientists and other health care professionals who specialize in infectious diseases. It was founded in 1963 and is based in Arlington, Virginia. ...
guidelines, severe cases of blastomycosis and cases with central nervous system (CNS) involvement are treated initially with
amphotericin B Amphotericin B is an antifungal medication used for serious fungal infections and leishmaniasis. The fungal infections it is used to treat include mucormycosis, aspergillosis, blastomycosis, candidiasis, coccidioidomycosis, and cryptococcosis. Fo ...
, followed by a lengthy course of an azole drug such as
itraconazole Itraconazole, sometimes abbreviated ITZ, is an antifungal medication used to treat a number of fungal infections. This includes aspergillosis, blastomycosis, coccidioidomycosis, histoplasmosis, and paracoccidioidomycosis. It may be given by mouth ...
. In most cases the amphotericin treatment lasts for 1–2 weeks, but in cases of CNS involvement it may last for up to 6 weeks. Cases that do not require amphotericin B treatment are treated with a lengthy course of an azole drug. Among azole drugs,
itraconazole Itraconazole, sometimes abbreviated ITZ, is an antifungal medication used to treat a number of fungal infections. This includes aspergillosis, blastomycosis, coccidioidomycosis, histoplasmosis, and paracoccidioidomycosis. It may be given by mouth ...
is generally the treatment of choice.
Voriconazole Voriconazole, sold under the brand name Vfend among others, is an antifungal medication used to treat a number of fungal infections. This includes aspergillosis, candidiasis, coccidioidomycosis, histoplasmosis, penicilliosis, and infections by '' ...
is often recommended for CNS blastomycosis cases due to its ability to pass the
blood–brain barrier The blood–brain barrier (BBB) is a highly selective semipermeable membrane, semipermeable border of endothelium, endothelial cells that prevents solutes in the circulating blood from ''non-selectively'' crossing into the extracellular fluid of ...
. Other azole drugs that may be used include
fluconazole Fluconazole is an antifungal medication used for a number of fungal infections. This includes candidiasis, blastomycosis, coccidiodomycosis, cryptococcosis, histoplasmosis, dermatophytosis, and pityriasis versicolor. It is also used to prevent ...
.
Ketoconazole Ketoconazole, sold under the brand name Nizoral among others, is an antiandrogen and antifungal medication used to treat a number of fungal infections. Applied to the skin it is used for fungal skin infections such as tinea, cutaneous candid ...
was the azole drug first used for blastomycosis treatment, but has been largely replaced by itraconazole because ketoconazole is less effective and less tolerated by patients. The azole treatment generally lasts for a minimum of six months. Cure rates from itraconazole treatment are nearly 95%.
Relapse In internal medicine, relapse or recidivism is a recurrence of a past (typically medical) condition. For example, multiple sclerosis and malaria often exhibit peaks of activity and sometimes very long periods of dormancy, followed by relapse or r ...
is rare but does occur even after a full course of treatment.


Prognosis

Published estimates of the
case fatality rate In epidemiology, case fatality rate (CFR) – or sometimes more accurately case-fatality risk – is the proportion of people diagnosed with a certain disease, who end up dying of it. Unlike a disease's mortality rate, the CFR does not take int ...
for blastomycosis have varied from 4% to 78%. A 2020 meta-analysis of published studies found an overall mortality rate of 6.6%. This rose to 37% for immunocompromised patients and 75% for patients with ARDS. A 2021 analysis of 20 years of
disease surveillance Disease surveillance is an epidemiological practice by which the spread of disease is monitored in order to establish patterns of progression. The main role of disease surveillance is to predict, observe, and minimize the harm caused by outbreak, ...
data from the five US states where blastomycosis is reportable found an overall mortality rate of 8% and a hospitalization rate of 57%. These numbers may be affected by the under-reporting of mild cases.


Epidemiology

Incidence in most endemic areas is about 0.5 per 100,000 population, with occasional local areas attaining as high as 12 per 100,000. Most Canadian data fit this picture. In Ontario, Canada, considering both endemic and non-endemic areas, the overall incidence is around 0.3 cases per 100,000; northern Ontario, mostly endemic, has 2.44 per 100,000.
Manitoba Manitoba ( ) is a Provinces and territories of Canada, province of Canada at the Centre of Canada, longitudinal centre of the country. It is Canada's Population of Canada by province and territory, fifth-most populous province, with a population o ...
is calculated at 0.62 cases per 100,000. Remarkably higher incidence was shown for the
Kenora, Ontario Kenora (), previously named Rat Portage (french: Portage-aux-Rats), is a city situated on the Lake of the Woods in Ontario, Canada, close to the Manitoba boundary, and about east of Winnipeg by road. It is the seat of Kenora District. The hist ...
region: 117 per 100,000 overall, with aboriginal reserve communities experiencing 404.9 per 100,000. In the United States, the incidence of blastomycosis is similarly high in hyperendemic areas. For example, the city of Eagle River, Vilas County, Wisconsin, which has an incidence rate of 101.3 per 100,000; the county as a whole has been shown in two successive studies to have an incidence of about 40 cases per 100,000. An incidence of 277 per 100,000 was roughly calculated based on 9 cases seen in a Wisconsin aboriginal reservation during a time in which extensive excavation was done for new housing construction. The new case rates are greater in northern states such as
Wisconsin Wisconsin () is a state in the upper Midwestern United States. Wisconsin is the 25th-largest state by total area and the 20th-most populous. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake M ...
, where from 1986 to 1995 there were 1.4 cases per 100,000 people. The study of outbreaks as well as trends in individual cases of blastomycosis has clarified a number of important matters. Some of these relate to the ongoing effort to understand the source of infectious inoculum of this species, while others relate to which groups of people are especially likely to become infected. Human blastomycosis is primarily associated with forested areas and open watersheds; It primarily affects otherwise healthy, vigorous people, mostly middle-aged, who acquire the disease while working or undertaking recreational activities in sites conventionally considered clean, healthy and in many cases beautiful. Repeatedly associated activities include hunting, especially raccoon hunting, where accompanying dogs also tend to be affected, as well as working with wood or plant material in forested or riparian areas, involvement in forestry in highly endemic areas, excavation, fishing and possibly gardening and trapping.


Urban infections

There is also a developing profile of urban and other domestic blastomycosis cases, beginning with an outbreak tentatively attributed to construction dust in
Westmont, Illinois Westmont is a village in DuPage County, Illinois, United States. Westmont is a community of 5.03 square miles in area with a 2010 population of 24,685. It is located approximately west of the Chicago Loop in the southeastern portion of DuPage Co ...
. The city of
Rockford, Illinois Rockford is a city in Winnebago County, Illinois, located in the far northern part of the state. Situated on the banks of the Rock River, Rockford is the county seat of Winnebago County (a small portion of the city is located in Ogle County). ...
, was also documented as a hyperendemic area based on incidence rates as high as 6.67 per 100,000 population for some areas of the city. Though proximity to open watersheds was linked to incidence in some areas, suggesting that outdoor activity within the city may be connected to many cases, there is also an increasing body of evidence that even the interiors of buildings may be risk areas. An early case concerned a prisoner who was confined to prison during the whole of his likely blastomycotic incubation period. An epidemiological survey found that although many patients who contracted blastomycosis had engaged in fishing, hunting, gardening, outdoor work and excavation, the most strongly linked association in patients was living or visiting near waterways. Based on a similar finding in a Louisiana study, it has been suggested that place of residence might be the most important single factor in blastomycosis epidemiology in north central
Wisconsin Wisconsin () is a state in the upper Midwestern United States. Wisconsin is the 25th-largest state by total area and the 20th-most populous. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake M ...
. Follow-up epidemiological and case studies indicated that clusters of cases were often associated with particular domiciles, often spread out over a period of years, and that there were uncommon but regularly occurring cases in which pets kept mostly or entirely indoors, in particular cats, contracted blastomycosis. The occurrence of blastomycosis, then, is an issue strongly linked to housing and domestic circumstances.


Seasonal trends

Seasonality and weather also appear to be linked to contraction of blastomycosis. Many studies have suggested an association between blastomycosis contraction and cool to moderately warm, moist periods of the spring and autumn or, in relatively warm winter areas. However, the entire summer or a known summer exposure date is included in the association in some studies. Occasional studies fail to detect a seasonal link. In terms of weather, both unusually dry weather and unusually moist weather have been cited. The seemingly contradictory data can most likely be reconciled by proposing that ''B. dermatitidis'' prospers in its natural habitats in times of moisture and moderate warmth, but that inoculum formed during these periods remains alive for some time and can be released into the air by subsequent dust formation under dry conditions. Indeed, dust per se or construction potentially linked to dust has been associated with several outbreaks The data, then, tend to link blastomycosis to all weather, climate and atmospheric conditions except freezing weather, periods of snow cover, and extended periods of hot, dry summer weather in which soil is not agitated.


Gender bias

Sex is another factor inconstantly linked to contraction of blastomycosis: though many studies show more men than women affected, some show no sex-related bias. As mentioned above, most cases are in middle aged adults, but all age groups are affected, and cases in children are not uncommon.


Ethnic populations

Ethnic group or race is frequently investigated in epidemiological studies of blastomycosis, but is potentially confounded by differences in residence and in quality and accessibility of medical care, factors that have not been stringently controlled for to date. In the United States, some studies show a disproportionately high incidence and/or mortality rate for blastomycosis among
Black people Black is a racialized classification of people, usually a political and skin color-based category for specific populations with a mid to dark brown complexion. Not all people considered "black" have dark skin; in certain countries, often in s ...
. In Canada, some studies, but not others, indicate that First Nations people have a disproportionately high incidence of blastomycosis. Incidence in First Nations children may be unusually high. The Canadian data in some areas may be confounded or explained by the tendency to establish indigenous communities in wooded, riparian, northern areas corresponding to the core habitat of ''B. dermatitidis'', often with known ''B. dermatitidis'' habitats such as woodpiles and beaver constructions in the near vicinity.


Communicability

Blastomycosis is not considered contagious, either among humans or between animals and humans. However, there are a very small number of cases of human-to-human transmission of ''B. dermatitidis'' related to dermal contact or sexual transmission of disseminated blastomycosis of the genital tract among spouses.


History

The organisms causing blastomycosis have existed for millions of years. The pathogenic group of onygenalean fungi that give rise to conditions including blastomycosis and histoplasmosis emerged approximately 150 million years ago. The most closely related blastomycosis-causing fungi, ''Blastomyces dermatitidis'' and ''Blastomyces gilchristii'', diverged during the
Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...
, approximately 1.9 million years ago. At the
Koster Site The Koster Site is a prehistoric archaeological site located south of Eldred, Illinois. The site covers more than 3 acres and extends 30 feet down into the alluvial deposits of the Illinois River valley. Over the course of its excavation betw ...
in Illinois, evidence pointing to possible blastomycosis infections among
Late Woodland In the classification of archaeological cultures of North America, the Woodland period of North American pre-Columbian cultures spanned a period from roughly 1000 BCE to European contact in the eastern part of North America, with some archaeolog ...
Native Americans has been identified. At that site, Dr. Jane Buikstra found evidence for what may have been an epidemic of a serious spinal disease in adolescents and young adults. Several of the skeletons showed lesions in the spinal vertebrae in the lower back. There are two modern diseases that produce lesions in the bone similar to the ones Dr. Buikstra found in these prehistoric specimens: spinal TB and blastomycosis. The bony lesions in these two diseases are practically identical. Blastomycosis seems more probable as these young people in Late Woodland and Mississippian times may have been affected because they were spending more time cultivating plants than their Middle Woodland predecessors had done. If true, it would be another severe penalty Late Woodland people had to pay as they shifted to agriculture as a way of life, and it would be a contributing factor to shortening their lifespans compared to those of the Middle Woodland people. Blastomycosis was first described by
Thomas Caspar Gilchrist Thomas Caspar Gilchrist (15 June 1862-14 November 1927), was professor of dermatology at the University of Maryland before taking up the same position at the Johns Hopkins Hospital, Baltimore. He wrote on acne, erysipelas Erysipelas () is a re ...
in 1894, as a skin disease. Because of this, blastomycosis is sometimes called "Gilchrist's disease". Gilchrist initially identified the cause of the disease as a
protozoan Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...
, but later correctly identified it as a fungus. In 1898 he and William Royal Stokes published the first description of ''Blastomyces dermatitidis''. Gilchrist referred to the disease as "blastomycetic dermatitis". The systemic spread of blastomycosis was first described in 1902, in a case that had been misdiagnosed as a combination of tuberculosis and a blastomycosis skin infection. In 1907, the dimorphic nature of the ''Blastomyces'' fungus was first identified. In 1912, the first case of canine blastomycosis was reported. Prior to the 1930s, blastomycosis was not clearly distinguished from similar fungal conditions. A paper by Rhoda Williams Benham in 1934 distinguished the causative agent of blastomycosis from
cryptococcosis Cryptococcosis is a potentially fatal fungal infection of mainly the lungs, presenting as a pneumonia, and brain, where it appears as a meningitis. Cough, difficulty breathing, chest pain and fever are seen when the lungs are infected. When the ...
and
coccidioidomycosis Coccidioidomycosis (, ), commonly known as cocci, Valley fever, as well as California fever, desert rheumatism, or San Joaquin Valley fever, is a mammalian fungal disease caused by ''Coccidioides immitis'' or ''Coccidioides posadasii''. Coccidio ...
. In the early 1950s, blastomycosis was first determined to be a primarily respiratory disease, with most skin lesions caused by systemic spread from an initial lung infection. In 1952, the first documented case outside North or Central America, in
Tunisia ) , image_map = Tunisia location (orthographic projection).svg , map_caption = Location of Tunisia in northern Africa , image_map2 = , capital = Tunis , largest_city = capital , ...
, was reported. The 1950s also saw the first introduction of
antifungal An antifungal medication, also known as an antimycotic medication, is a pharmaceutical fungicide or fungistatic used to treat and prevent mycosis such as athlete's foot, ringworm, candidiasis (thrush), serious systemic infections such as crypto ...
drugs including
amphotericin B Amphotericin B is an antifungal medication used for serious fungal infections and leishmaniasis. The fungal infections it is used to treat include mucormycosis, aspergillosis, blastomycosis, candidiasis, coccidioidomycosis, and cryptococcosis. Fo ...
. Before 1950, the fatality rate for disseminated blastomycosis was 92%, and treatment options were limited to iodide compounds, radiation therapy, and surgery. The first azole antifungal drug,
ketoconazole Ketoconazole, sold under the brand name Nizoral among others, is an antiandrogen and antifungal medication used to treat a number of fungal infections. Applied to the skin it is used for fungal skin infections such as tinea, cutaneous candid ...
, was developed in the 1970s and approved in the United States in 1981. Prior to 2013, the only species known to cause blastomycosis was ''B. dermatitidis''. Since that time, genomic analysis has identified multiple other ''Blastomyces'' species causing blastomycosis, including ''B. gilchristii'' (2013), ''B. helicus'' (reassigned from the genus ''
Emmonsia ''Chrysosporium'' is a genus of hyaline hyphomycetes fungi in the family Onygenaceae. ''Chrysosporium'' colonies are moderately fast-growing, flat, white to tan to beige in color; they often have a powdery or granular surface texture. Hyaline, ...
'' in 2017), ''B. percursus'' (2017), and ''B. emzantsi'' (2020).


Other animals

Blastomycosis affects a broad range of
mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s. As with humans, most animals that become infected were formerly healthy and immunocompetent. Dogs are frequently affected; blastomycosis is eight to ten times more common in dogs than in humans. Sporting and
hound A hound is a type of hunting dog used by hunters to track or chase prey. Description Hounds can be contrasted with gun dogs that assist hunters by identifying prey and/or recovering shot quarry. The hound breeds were the first hunting dogs. T ...
breeds are at the greatest risk. Cats and horses can also be infected. Cats with
feline immunodeficiency virus Feline immunodeficiency virus (FIV) is a '' Lentivirus'' that affects cats worldwide, with 2.5% to 4.4% of felines being infected. FIV was first isolated in 1986, by Niels C Pedersen and Janet K. Yamamoto at the UC Davis School of Veterina ...
are particularly at risk. However, the overall risk of blastomycosis in cats is 28 to 100 times lower than in dogs. Cases of blastomycosis have also been reported in captive
lion The lion (''Panthera leo'') is a large Felidae, cat of the genus ''Panthera'' native to Africa and India. It has a muscular, broad-chested body; short, rounded head; round ears; and a hairy tuft at the end of its tail. It is sexually dimorphi ...
s and
tiger The tiger (''Panthera tigris'') is the largest living cat species and a member of the genus '' Panthera''. It is most recognisable for its dark vertical stripes on orange fur with a white underside. An apex predator, it primarily preys on u ...
s, in a wild North American black bear, and in marine mammals such as the Atlantic bottlenose dolphin. The nonspecific symptoms that make blastomycosis difficult to diagnose in humans also complicate veterinary diagnosis. Cats in particular are often only diagnosed after death. Dogs and humans frequently acquire blastomycosis from the same exposure event. In most such cases, the infection in the dog becomes apparent before the human infection. This may be due to a shortened incubation period, caused by the dog inhaling larger quantities of ''Blastomyces'' spores than the human. In veterinary care, blastomycosis is typically treated with
itraconazole Itraconazole, sometimes abbreviated ITZ, is an antifungal medication used to treat a number of fungal infections. This includes aspergillosis, blastomycosis, coccidioidomycosis, histoplasmosis, and paracoccidioidomycosis. It may be given by mouth ...
. 70% of treated dogs respond to medication and recover. In dogs as in humans, the prognosis for blastomycosis depends on the severity of the symptoms.


Additional images

File:North American blastomycosis 1.jpg, Granuloma with early suppuration. Fungal organisms difficult to recognize at this low magnification. File:North American blastomycosis 2.jpg, Large yeast-like fungi seen within giant cells at arrows. File:North American blastomycosis 3.jpg, Large yeast-like fungi seen within giant cells at arrows. Budding yeasts in cytoplasm of giant cells at arrows. Broad-based budding and double contoured cell wall seen in the giant cell in the center is characteristic of Blastomyces dermatitidis. File:Blastomycosis of skin.jpg, Nodular skin lesions of blastomycosis, one of which is a bullous lesion on top of a nodule.


See also

*
Histoplasmosis Histoplasmosis is a fungal infection caused by ''Histoplasma capsulatum''. Symptoms of this infection vary greatly, but the disease affects primarily the lungs. Occasionally, other organs are affected; called disseminated histoplasmosis, it can ...
*
Paracoccidioidomycosis Paracoccidioidomycosis (PCM), also known as South American blastomycosis, is a fungal infection that can occur as a mouth and skin type, lymphangitic type, multi-organ involvement type (particularly lungs), or mixed type. If there are mouth ulcer ...


References


Further reading

* (Review). * (Review)


External links

* *
NIH Encyclopedia Blastomycosis
{{Mycoses, state=collapsed Animal fungal diseases Mycosis-related cutaneous conditions Fungal diseases