Syntopic Timber Rattlesnake and Eastern Copperhead exhibit different responses to the same assemblage of infectious diseases

Tadevosyan, Tigran

tigran@oxbowassociates.com

Oxbow Associates, Inc.                                                                                                                                   

P.O. Box 971                                                                                                                                                      

Acton, Massachusetts USA

Mertz, Gregory                                                                                                                                                   

New England Wildlife Center                                                                                                                             

500 Columbian Street                                                                                                                                   

Weymouth, Massachusetts USA

Kemmett, Dominic                                                                                                                                       

Oxbow Associates Inc.                                                                                                                                    

P.O. Box 971                                                                                                                                         

Acton, Massachusetts USA

Prevalence of lesions associated with Ophidiomycosis and concurrent bacterial infections varies geographically and between species. Between 2022 and 2024 during spring emergence, we captured and examined Timber Rattlesnakes (Crotalus horridus: n = 78) and Eastern Copperheads (Agkistrodon contortrix: n = 128) from syntopic populations in Norfolk County, Massachusetts. The probability of having lesions were significantly higher (logistic regression: p = 0.003) in rattlesnakes (31 - 39.7%) than in copperheads (16 - 12.5%), and were higher in 2024 than in previous years (p < 0.02). Sex, age, snout-vent length (SVL), and Body Condition Index (BCI) did not predict lesions. We scored severity of lesions = (Cranial Score:[largest lesion size (1U3)/10+Subdermal (1)] + (Body Score: [largest lesion size (1U3)/20+Subdermal (1)]) + (Ventral Score: [ventral scutes/20+Subdermal (1)]) + (Vent to Tail Score: [largest lesion size (1U3)/10+Subdermal (1)]. Total lesion scores were only marginally affected by fitness (BCI; GLM: p = 0.051), but cranial lesions directly impacting sensory functions were associated with decreased BCI (p < 0.005). Lesions were differently represented in age-size classes of more robust rattlesnakes and on average, slightly smaller copperheads. In C. horridus, the occurrence of lesions was comparatively high in all size classes, and was correlated with encounter rates per size class (R-squared = 0.66). In A. contortrix,  lesion and encounter rates, per size class were not correlated (R-squared = 0.03); lesion rates were zero in individuals < 500 mm SVL, but were maximal in 500-600 mm and 700-800 mm groups, and then decreased, along with encounter rates in larger copperheads. We hypothesize that individual copperheads may exhibit more rapid mortality from infections, which may beneficially reduce the spread of pathogens. In contrast, adult rattlesnakes appear to live longer with infection, thus developing substantial lesions which may result in higher observable prevalence and persistence of infection reservoirs.pear to live longer with infection, thus developing substantial lesions which may result in higher observable prevalence and persistence of infection reservoirs.