Histoplasma capsulatum Flashcards
Structure
dimorphic fungus- hyphae in soil and budding yeast in host tissues
Distribution
worldwide, found in both temperate and tropical zones
Where does it like to breed?
usually in soil enriched by bird bat feces, birds can’t sustain infection so limited contamination risk
Soil pH
5-10
Reservoir hosts
bats, believed to infect ameba as well
Sexual reproduction
haploid nuclei of two opposite mating types fuse to form a diploid nucleus-> divides by meiosis and produces ascospores
Asexual reproduction
reproduce by mitotic division (conidiation), production of vegetative budding spores; macroconidia and microconidia-> germinate in soil-> can adopt either yeast or mold form
Transmission cycle
when soil disrupted-> conidia and fragments of hyphal mycelia become aerosolized and are inhaled-> once in lungs, germinate with distal bronchioles and pulmonary alveoli-> convert to budding yeast-> phagocytized by immune cells-> reaches regional lymph nodes-> spreads to other parts of body through blood stream
Specific in bats (transmission cycle)
yeast make it into GI tract and excreted in feces
Pathogenesis
prefer intracellular budding-> want to be phagocytosed-> can lead to granuloma formation in similar pathway as TB
Incubation
3-21 days
Extent of damage highly dependent on
amount of conidia inhaled, host’s immune system, virulence of strain
Clinical signs
weight loss, fever, pale mucous membranes, peripheral lymphadenopathy, tachypnea, hepatomegaly, ascites, diarrhea
Pathologic lesions
miliary nodules within lungs, lymphadenopathy hepatomegaly, splenomegaly, ascites, thickened and hemorrhagic intestines
histologic lesions: granulomatous inflammation with intralesional yeasts in affected tissues, fibrosis
Diagnosis
microscopic slides, thoracic radiographs, histoplasma skin test, ELISA, radioimmunoassay, restriction fragment length polymorphisms and polymerase chain reaction (PCR) based DNA fingerprinting
