Positivity Rate of Ophidiomyces ophidiicola in Snake Populations of Cook County, Illinois, USA.

Ophidiomycosis, caused by Ophidiomyces ophidiicola, is a disease associated with variably high morbidity and mortality in both snakes under human care and free-living snakes. Within Illinois, USA, ophidiomycosis surveillance has primarily focused on snake populations in southern Illinois, adjacent to agricultural land. The purpose of this study was to determine the occurrence of O. ophidiicola DNA across multiple snake species and locations in an urban county of northeastern Illinois, containing historically diverse and abundant snake populations. During the summer of 2023, 51 snakes, representing five species, were collected, examined, and evaluated via skin swab for the presence of O. ophidiicola using quantitative PCR. Detection of O. ophidiicola was similar between seven distinct sites and five species: 31% (9/29) in common water snakes (Nerodia sipedon), 29% (2/7) in eastern fox snakes (Pantherophis vulpinus), 17% (1/6) in DeKay's brownsnakes (Storeria dekayi), 40% (2/5) in common garter snakes (Thamnophis sirtalis), and 50% (2/4) in eastern milk snakes (Lampropeltis triangulum). Gross lesions consistent with O. ophidiicola infection, including crusts, discoloration, swelling, and ulceration, were noted in 65% (33/51) of the snakes sampled in the study and 75% (12/16) of the O. ophidiicola-positive snakes. Results indicate that O. ophidiicola in snakes in northeastern Illinois exists at a similar or higher positivity rate than has been documented in other studies across North America. Future studies may enable improved characterization of ophidiomycosis dynamics.