Blastomycosis

Blastomycosis is a fungal infection caused by inhaling Blastomyces dermatitidis spores.

North American blastomyclosis

Definition

Blastocystis is a common microscopic organism that inhabits the intestine and is found throughout the world. A full understanding of the biology of Blastocystis and its relationship to other organisms is not clear, but is an active area of research. Infection with Blastocystis is called blastocystosis.

Signs and symptoms

Watery or loose stools, diarrhea, abdominal pain, anal itching, weight loss, constipation, and excess gas have all been reported in persons with Blastocystis infection. Many people have no symptoms at all. The organism can be found in both well and sick persons.

Blastocystis can remain in the intestine for weeks, months, or years.

Distribution of blastomycosis in North America

Cause

The role of Blastocystis in causing disease is controversial among experts. Some types of Blastocystis may be more likely to be associated with symptoms. Finding Blastocystis in stool samples should be followed up with a careful search for other possible causes of your symptoms.

Incidence

Many people have Blastocystis in their intestine, some without ever having symptoms.

Transmission

How Blastocystis is transmitted is not known for certain, although the number of people infected seems to increase in areas where sanitation and personal hygiene is not adequate. Studies have suggested that risk of infection may increase through:

Blastomycosis

• ingesting contaminated food or water,
• exposure to a day care environment, or
• exposure to animals.
• How can I prevent infection with Blastocystis?
• Wash your hands with soap and warm water after using the toilet, changing diapers, and before handling food.
• Teach children the importance of washing hands to prevent infection.
• Avoid water or food that may be contaminated.
• Wash and peel all raw vegetables and fruits before eating.
• When traveling in countries where the water supply may be unsafe, avoid drinking unboiled tap water and avoid uncooked foods washed with unboiled tap water.
• Bottled or canned carbonated beverages, seltzers, pasteurized fruit drinks, and steaming hot coffee and tea are safe to drink.

Treatment

The clinical significance of Blastocystis spp. is controversial.

Treatment with metronidazole^ at various doses has been reported, for example (adults):

250 mg to 750 mg metronidazole^ orally 3 times daily for 10 days 1500 mg metronidazole^ orally once daily for 10 days Note: Lack of response to metronidazole has been noted in some areas (Yakoob et al., Br J Biomed Sci 2004;61:75).

Blastomycosis of skin

Treatment with trimethoprim (TMP)^/sulfamethoxazole (SMX)^ at various doses has been reported, for example (adults):

6 mg/kg TMP^, 30 mg/kg SMX^ once daily for 7 days 320mg TMP^, 1600 mg SMX^ once daily for 7 days 160 mg TMP^, 800 mg SMX^ twice daily for 7 days Treatment with nitazoxanide^ has been shown to be effective in clearing organisms and improving symptoms at the following doses:

Adults, 500 mg nitazoxanide^ orally twice daily for 3 days. Children, 200 mg nitazoxanide^ orally twice daily for 3 days in patients aged 4–11 years, and 100 mg nitazoxanide^ orally twice daily for 3 days in patients aged 1–3 years. Tinidazole^, paromomycin^, iodoquinol^, and ketoconazole^ have also been used for clearing Blastocystis, as presented in case reports or small series (see references).

^Not FDA-approved for this indication.

Blastomyces dermatitis is found in the soil and decaying organic matter like wood or leaves

Blastomycosis is endemic to the eastern United States, especially the Ohio and Mississippi River valleys, the Great Lakes, and the St. Lawrence River. It is also endemic to some parts of Canada, including Quebec, Ontario, and Manitoba.

Prognosis

Mortality rate in treated cases

• 0-2% in treated cases among immunocompetent patients
• 29% in immunocompromised patients
• 40% in the subgroup of patients with AIDS
• 68% in patients presenting as acute respiratory distress syndrome (ARDS)

Epidemiology

[[Image:Blasto-map 600.jpg|thumb|Distribution of blastomycosis in North America based on the map given by Kwon-Chung and Bennett, with modifications made according to case reports from a series of additional sources.

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.

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  Granuloma with early suppuration. Fungal organisms difficult to recognize at this low magnification.

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  Large yeast-like fungi seen within giant cells at arrows.

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  Large yeast-like fungi seen within giant cells at arrows.Budding yeasts in cytoplasm of giant cells at arrows. Broad-based budding and double countoured cell wall seen in the giant cell in the center is characteristic of Blastomyces dermatitidis.

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.

Gender bias

Sex is another factor inconstantly linked to contraction of blastomycosis: though many studies show more men than women affected.

Ethnic populations

Ethnic group or race is frequently investigated in epidemiological studies of blastomycosis, but is potentially profoundly conflicted by differences in residence and in quality and accessibility of medical care, factors that have not been stringently controlled for to date.

Communicability

There are a very small number of cases of human-to-human transmission of B. dermatitidis related to dermal contact.

Other animals

Blastomycosis also affects an indefinitely broad range of mammalian hosts, and dogs in particular are a highly vulnerable sentinel species.

See also

• Histoplasmosis
• Paracoccidioidomycosis