Pathologic Characterization of Raillietiella orientalis Infection and Comorbidities in Free-Ranging Pygmy Rattlesnakes (Sistrurus miliarius) from Central Florida, USA

Raillietiella orientalis (Ro) is a parasitic pentastome with a rapidly expanding geographic and herpetofaunal host range in the southeastern USA since its introduction, probably with the invasive Burmese python (Python bivittatus). However, little is known about the health impacts of Ro infection in native USA host species. Pygmy rattlesnakes (Sistrurus miliarius), small pit vipers native to the southeastern USA, were among the first documented naïve hosts of Ro in Florida, USA. Between December 2018 and February 2019, 17 free-ranging S. miliarius from central Florida were evaluated for Ro pentastomiasis and comorbidities. Necropsy revealed Ro pentastomiasis in eight (47%) rattlesnakes confirmed by morphologic and molecular methods. Pygmy rattlesnakes harbored more Ro pentastomes (mean) than documented in Burmese pythons in southern Florida; moreover, the mean length of mature female Ro in S. miliarius was greater than in pythons, suggesting altered host-parasite interactions in this naïve host. Microscopically, localized inflammation and parasitic hematin deposition were associated with Ro in respiratory and coelomic tissues. All 17 snakes (100%) had both fungal dermatitis consistent with ophidiomycosis and mixed endoparasitism; other findings included two (12%) snakes with ferlaviral pneumonia and one (6%) with gastric cryptosporidiosis. This study shows that although lesions directly attributable to Ro in S. miliarius were mild, mixed-pathogen coinfections were common, highlighting the need for further study of potential host health and fitness impacts in native Florida snakes.