Evaluation of Pathogenesis and Immune Response to Coccidi-oides posadasii Infection in U.S. Feral Swine (Sus scrofa)

The dimorphic, soil-dwelling fungus Coccidioides is the causative agent of coccidioidomycosis and is a reemerging pathogen of human health concern. Despite increasing incidence and isolations of the organism outside of its theoretical environmental range, much of Coccidioides epidemiology, including complete host range, remains unknown. Feral swine (Sus scrofa) are an invasive species distributed throughout the United States that may play a role in fungal ecology due to their behavioral associations with soil. To address this, we evaluated seven feral swine for susceptibility to Coccidioides. After intranasal inoculation with 106.2 arthroconidia of C. posadasii, no pigs displayed signs of clinical disease, nor did any exhibit antibodies by AGID testing. Histopathologic evaluation did not reveal the presence granulomatous lesions, and fungal spherules or endospores were not observed in any of the tissue sections examined, although individuals had significant comorbidities, most notably Metastrongylus nematodes in the lungs. Despite the absence of lesions and organisms histologically, C. posadasii was isolated by culture from the lung and mediastinal lymph node of two pigs, indicating active infection. These results suggest that feral swine are mildly susceptible to acute Coccidioides infection and may aid in fungal dispersal due to the presence of spherules in tissues post-mortem.