Crows, and other members of the Corvid family, have been implicated in helping to spread the mosquito-borne West Nile virus (WNV) throughout the U.S. However, it is more correct to consider crows and related species as the first victims of WNV, not the vectors. However, crows may yet be found to be a significant factor in the spread of WNV, but this is not known with any certainty at this time; research continues.
Also, crows, at times, feed in and around farm buildings, where they have been implicated in the spread of transmissible gastroenteritis (TGE) among swine facilities.
Large crow flocks near wetland areas may increase the potential for spread of waterfowl diseases such as avian cholera. The scavenging habits of crows and the apparent longer incubation time of the disease in crows are factors that increase the potential for crows to spread this devastating disease.
Also, roosts of crow and other bird species (blackbird, starling) that have been in place for some years may harbor the fungus Histoplasma capsulatum, a disease that causes histoplasmosis, a disease that can infect people who breathe in spores when a roost is disturbed.