Epizootiology of cranial abscess disease in white-tailed deer
Cohen, Bradley Stephen
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Cranial abscess disease is a cause of morbidity and mortality, particularly for mature, male white-tailed deer (Odocoileus virginianus). Most cases of cranial abscesses are associated with infection by Trueperella (Arcanobacterium) pyogenes but little is known about the epidemiology of this disease. I isolated T. pyogenes 46 of 65 (71%) active cranial abscess infections. All of these isolates had at least six of eight virulence genes which further implicates this bacterium as an important etiological agent. I also examined 7,545 white-tailed deer from 60 sites across Georgia for signs of cranial abscess disease to determine the distribution and risk factors for the disease. None of the 2,562 female deer examined had the disease, whereas 91 of the 4,983 (1.8%) male white-tailed deer had abscesses. A generalized linear mixed model examining the risk of a male having cranial abscess disease and treating property as a random effect suggested that age was the most important risk factor. Habitat variables (e.g., evergreen forest cover, agriculture, etc.) and soil features were not strongly associated with increasing risk. Because the model suggested that a large amount of variance occurred at the property level, I examined variation in the occurrence virulence determinants in the genome of T. pyogenes between sites affected and unaffected by the disease. Using polymerase Chain Reaction (PCR), six of seven virulence determinants, all of which code for proteins promoting bacterial adhesion to epithelium, were more common on properties where abscesses were found (p<0.05). Thus the patchy distribution of cranial abscess disease across Georgia is likely caused by differences in the genetics of the causative agent, T. pyogenes. White-tailed deer managers must recognize the potential to transport pathogenic bacteria and disease when relocating white-tailed deer.