References:
- Global Infectious Diseases and Epidemiology Online Network: Infectious Diseases of the Philippines, 2013 eBook Edition, ISBN 978-1-61755-582-4, by Stephen Berger. Accessed here.
| Agent | FUNGUS. Ascomycota, Euascomycetes, Onygenales: Histoplasma capsulatum var. capsulatum A dimorphic fungus |
| Reservoir | Soil Caves Chicken roosts Bat |
| Vector | None |
| Vehicle | Air |
| Incubation Period | 10 to 14 days (As early or late as 5 to 25 days) |
| Diagnostic Tests | Fungal culture Serologic tests less helpful Antigen tests currently under study Nucleic acid amplification |
| Typical Adult Therapy | Itraconazole 200 mg daily X 9m For severe or immunocompromized patients: Amphotericin B 0.4 mg/kg/d X 6w, then 0.8 mg/kg qod X 8w |
| Typical Pediatric Therapy | Itraconazole 2 mg/kg daily X 9 m. For severe or immunocompromized patients: Amphotericin B 0.4 mg/kg/d X 6w, then 0.8 mg/kg qod X 8w |
| Clinical Hints | Fever, cough, myalgia, pulmonary infiltrates and calcifying hilar lymphadenopathy; chronic multisystem infection often encountered. |
| Synonyms | Darling’s disease, Histoplasma capsulatum, Histoplasmose, Ohio River Valley Fever, Ohio Valley disease, Reticuloendothelial cytomycosis. |
Asymptomatic infection is common, and may be found as an incidental finding on chest X-ray, or through serological or skin tests.
Pulmonary histoplasmosis is an acute benign respiratory infection is characterized by weakness, fever, chest pains, and cough.
- The severity of illness is related to the magnitude of the exposure.
- Chronic pulmonary infection occurs in persons with pre-existing lung diseases such as emphysema.
- The infection is most common in males over the age of 40.
- Chronic pulmonary lesions are characterized by extensive cavitation, but may resemble those of tuberculosis.
Disseminated histoplasmosis is seen in immunocompromised patients (AIDS, leukemia, corticosteroid therapy, anti-TNF therapy, etc.) and may be characterized by fever, anemia, hepatitis, pneumonia, pleuritis, pericarditis, acalculous cholecystitis, meningitis, atypical skin lesions (10% of cases) and ulcers of the mouth, tongue, nose, paranasal sinuses, esophagus, colon, and larynx.
- Associated findings include upper lobe cavitation with fibrosis (similar to tuberculosis); sclerosing mediastinitis with obstruction of the superior vena cava, pulmonary arteries and veins; esophagus; and constrictive pericarditis.
- Fungemia is most common in patients with immunosuppression or neutropenia (<3,000/mm³).
- Central nervous system infection can present at chronic meningitis, focal parenchymal lesions of the brain or spinal cord, stroke due to infected emboli, and diffuse encephalitis.
- Spinal infection may mimic tuberculosis spondylodiscitis.
- Adrenal masses and renal infection are occasionally reported and may mimic carcinoma.
- Peritoneal histoplasmosis has been reported as a complication of peritoneal dialysis.
- Epididymo-orchitis and prostatitis are occasionally reported.
- Gastrointestinal infection may mimic colonic carcinoma or abdominal tuberculosis.
- Dermatological manifestations include erythema nodosum, erythema multiforme, purpuric lesions, or the appearance of ulcerating verrucous plaques. Primary infection may present as a dermal nodule with regional adenopathy. Skin lesions may mimic secondary syphilis.
- Hypercalcemia has been reported in some cases.
“Ocular histoplasmosis syndrome” is characterized by peripapillary atrophy, punched out lesions, a macular disciform lesion or scar in one eye without vitritis.
- The role of Histoplasma capsulatum in this condition is unclear.
- Overt Histoplasma keratitis has been reported.
Acute disseminated infection is also seen in infants and young children and is marked by fever, cough, exhaustion and hepatosplenomegaly.
- Roentgenographic findings include multiple nodules (3 to 4 mm) changing into punctate calcifications; histoplasmoma (non-calcifying nodules <3 mm); a “target lesion” (i.e., central calcification); or hilar/mediastinal adenopathy (“popcorn” calcification).
Primary histoplasmosis of the mouth has been reported.