Thursday 12 March 2009
Definition : Histoplasmosis is a granulomatous disease caused by the intracellular dimorphic fungus Histoplasma capsulatum .
bone marrow aspirate with disseminated histoplasmosis
Hyphae of Histoplasma. Rarely seen unless intravascular, as in endocarditis
Histoplasma in a nerve / intraneural histoplasmosis
Histoplasma capsulatum is found most commonly in North America and Central America, but the fungus has been reported from diverse areas around the world.
In endemic areas infection occurs during day-to-day activities that lead to disruption and subsequent inhalation of soil contaminated with bird or bat guano.
In areas endemic to histoplasmosis the vast majority of infections are either asymptomatic or present as a mild illness that is never recognized as being histoplasmosis.
Clinically, histoplasmosis may present as a pulmonary (acute pulmonary histoplasmosis, chronic cavitary pulmonary histoplasmosis, granulomatous mediastinitis and mediastinal fibrosis) or a disseminated infection.
Disseminated histoplasmosis has become increasingly important with the advent of new and expanding population of immunocompromised patients.
Primary gastrointestinal infections are an uncommon presentation of the infection, almost always associated with disseminated form of the disease and/or immunodeficiency.
Symptomatic gastrointestinal tract infection is more common in AIDS patients and can mimic other AIDS associated opportunistic infections that cause diarrhoea. The colon is the most commonly involved site followed by small bowel with lesions presenting as ulcerations, polyps, strictures or perforations.
Histoplasmosis has been reported both in immunocompetent as well as immunocompromised patients with disseminated forms being more common in the latter group.
In HIV positive patients the prevalence of histoplasmosis varies from 5% to 32% depending on the endemicity of the disease. In HIV infected patients, working in chicken coops, CD4 count < 150 cells/μL and positive baseline complement fixing antibodies to histoplasma antigen have been identified as possible risk factors for histoplasmosis.
Diabetes mellitus and HIV infection are the most common co-morbid conditions.
Weight loss and fever were found to be the most common symptoms while on physical examination; oropharyngeal ulcers, hepatosplenomegaly and lymphadenopathy were the most common signs.
gastrointestinal tract infection
- ulcerative lesions in the rectum, ileum and oesophagus
- multiple intestinal hemorrhages
In disseminated histoplasmosis, the yield of blood and sputum culture has been reported to be 75% and 50%, respectively.
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