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Fungal Infections

Disease name and synonyms

Histoplasmosis – acute pulmonary

Fungi responsible 

Histoplasma capsulatum

Disease description

Most exposed individuals are asymptomatic or mild self-limiting illnesses. In endemic areas, most people either have positive skin tests or typical radiological features of lymph node or diffuse or multifocal parenchymal calcification, signifying prior exposure which was clinically unrecognised. If exposure is heavy, an actute illness 2-4 weeks after exposure may develop in which fever, myalgia, headache, cough, dyspnoea and chest discomfort predominate. Sometimes arthralgia and/or erythema nodosum occur. Mediastinal lymphadenopathy can be massive.

Frequency and global burden

Exposure is common in the areas in which histoplasmosis is endemic . However symptomatic disease is uncommon.

Underlying problems and at risk patients

Cavers (spelunkers) and those in the construction industry, doing excavation or demolishing or building new buildings, cleaning chicken coops and heavy outdoor work.  The organism thrives in bat and bird guano. The larger the inoculum, the more severe the illness.

Primary infection in immunocompromised patients, especially those with advanced HIV infection and taking corticosteroids can be severe and fatal.  (Progressive histolplasmosis)

Diagnostic testing

Culture is occasionally positive but is slow and can take 10-20 days, occasionally longer. The laboratory should be warned of the possibility of Histoplasma as it is a class 3 pathogen. Seroconversion of antibody in blood is the usual means of making the diagnosis of acute pulmonary histoplasmosis in non-immunocompromised patients. Histoplasma antigen and PCR may also be posiive in the acute phase and are important investigations in immunocompromised patients.

Treatments

Usually none, but if severe illness with high fever and hypoxia then intravenous lipid- associated amphotericin B for 1-2 weeks with oral corticosteroids (ie 30mg prednisolone daily). This should be followed by itraconazole 200mg twice daily. Therapeutic drug monitoring is recommended. The duration is uncertain, but no less than 12 weeks.

IDSA Clinical Practice Guidelines 2007

Outlook and prognosis

Usually excellent in immunocompetent patients. Rare complications of fibrosing mediastinitis and adrenal dysfunction.

Images


Acute pulmonary histoplasmosis in a caver (spelunker). 


Massive mediastinal mass of lymph nodes impinging on the oesophagus (see arrows) and affecting swallowing

Geographical distribution of Histoplasma/osis:

Histoplama -America
 

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