Histoplasma capsulatum is an intracellular dimorphic fungus that is distributed across the globe and is responsible for pulmonary histoplasmosis. Bats and birds are natural reservoirs for this pathogen, which is found in soils contaminated with these animals' excreta, grows in nature as a mold, and grows in the tissues of a susceptible host as a yeast. Transmission of the fungus occurs through inhalation of airborne spores. The clinical manifestation of primary pulmonary histoplasmosis, which is prevalent in some regions of North America, typically includes nonspecific symptoms like "fevers, malaise, chills, cough, weight loss, and wheezing." Importantly, the amount of fungal particles breathed and the host's immune status determine the severity of this fungal infection, with higher morbidity and mortality rates among immunocompromised individuals.
Pulmonary histoplasmosis is usually an acute, chronic, or disseminated infection and, like the primary form, resolves spontaneously or with antifungal therapy in immunocompetent hosts. Most pulmonary infections in immunocompetent hosts are asymptomatic, with acute pulmonary infections occurring after prolonged exposure to large quantities of spores. Conversely, in individuals with weakened immune systems, histoplasmosis frequently manifests as a disseminated illness, typically with a high mortality rate in untreated cases. Nevertheless, adequate therapy can significantly reduce the mortality rate.
The aim of this review was to emphasize the key aspects of H. capsulatum associated with pulmonary histoplasmosis, including geographic distribution of H. capsulatum, clinical presentation of pulmonary histoplasmosis, pathogenesis, immune response and virulence factors of H. capsulatum, pathophysiology of pulmonary histoplasmosis and COVID-19, diagnostic approaches, and treatment strategies.
