​Infectious Diseases and Microbiology - Histoplasmosis (Histoplasma capsulatum)

​Infectious Diseases and Microbiology - Histoplasmosis (Histoplasma capsulatum) 
The disease histoplasmosis
Histoplasma capsulatum is the causative agent of histoplasmosis, which is inhaled after contaminated soil is disturbed and aerosolized spores (microconidia) are released into the air. Although histoplasmosis is a global disease, it is endemic in the US in the Ohio and Mississippi River valleys. H capsulatum grows on soil, especially in soil that has been exposed to bat and bird droppings, especially those of starlings.
 More than 90% of infections are self-limiting, asymptomatic, and affect immunocompetent people.
In 1% of instances, there is chronic pulmonary and progressive histoplasmosis. This condition mainly affects immunocompromised individuals or results from exposure to a high organism inoculum. Although it is uncommon, solid organ transplant recipients and immunocompromised individuals with T-cell defects—such as those with AIDS—may develop disseminated histoplasmosis. In individuals with HIV or AIDS, the death rate from disseminated histoplasmosis is approximately 10%.
Pathophysiology When H capsulatum is inhaled, the microconidia develop intracellularly like yeast grows in macrophages. This process continues until the immune system reacts, causing a localized granuloma.
A component of disseminated histoplasmosis is the invasion of reticuloendothelial system cells. H capsulatum evades phagolysosomal death by raising the pH of lysosomes, which in turn deactivates the enzymes responsible for degradation.
lab Yeast is visible within macrophages when clinical specimens (tissue, sputum) are examined under a microscope and stained with Wright or Giemsa stain. Patients with disseminated illness can have their blood and urine tested for a H capsulatum-specific polysaccharide antigen using an enzyme immunoassay technique.
For initial infections, which are typically self-limited, there is no need for therapy. Amphotericin B and itraconazole are used to treat histoplasmosis. A preventive method is to stay out of high endemic areas.