Public Health Considerations
The potential role of bats in spreading H. capsulatum var. capsulatum remains unclear. However, the high risk of natural bat infection with this fungus in caves has been well-documented.
In a recent investigation in Mexico, lung samples from 122 bats were examined (Gonzalez-Gonzalez et al. 2014). A total of 98 samples revealed Histoplasma infection. Benedict and Mody (2016) provided an update on the epidemiologic features of 105 documented human outbreaks in the USA. The presence of bats (or bat droppings) was reported in 24 (23%) outbreaks and the presence of birds or bird droppings in 59 (56%). Birds most frequently involved were chickens (41% of bird-related outbreaks) and blackbirds (starlings, grackles), pigeons and gulls.Transmission of H. capsulatum from companion animals to humans has never been reported. However, infected pets may be a sentinel for human exposure, and this is especially relevant if the animal resides with immunocompromised human beings. Concurrent infections of owners and companion animals were reported after exposure to the same environment or source of infective material (Dillon et al. 1982, Davies and Colbert 1990). A common-source environmental exposure was also suggested in a study evaluating the geographical specificity of H. capsulatum var. capsulatum isolates in Brazil (de Medeiros Muniz et al. 2001). Using the MLST typing technique, Balajee et al. (2013) demonstrated that isolates from feline and human cases were genetically distinct. However, the feline cases were from California, Colorado and Texas, whereas the human cases were from different regions (Missouri and Georgia). This result might indicate that the genetic differences were related to geographic distance rather than to host specificity.