1Northwest ZooPath, Monroe, WA, USA; 2Progressive Animal Welfare Society Wildlife Center, Lynnwood, WA, USA; 3Electron Microscopy Laboratory, California Animal Health and Food Safety Laboratory, School of Veterinary Medicine, University of California, Davis, CA, USA
To the authors’ knowledge, there are no previous reports of any kind of poxvirus infection in bats. From 2009-2011, 6 big brown bats (Eptesicus fuscus) were submitted to Northwest ZooPath for histologic evaluation. All bats were adults found down and unable to fly in the late Spring or Summer. Five were males and sex was unknown for one. All but one of the bats had one or more visibly swollen and sometimes contused joints involving the long bones of the legs and wings, and one had contusions of the oral commissures. All bats received care that included antibiotics, nutritional and fluid support with minimal or no clinical improvement, progressive joint swelling and increased lethargy. All bats were eventually euthanatized. Gross lesions were limited to the joints in all bats. Histologically, all bats had severe fibrino-suppurative and necrotizing tenosynovitis and osteoarthritis with occasional localized vasculitis. No infectious agents were seen by light microscopy with hematoxylin and eosin, giemsa, Warthin-Starry, Brown and Brenn or Gomori methenamine-silver stains or in a Wright-Giemsa stained cytologic preparation of a joint aspirate. Aerobic, anaerobic and mycoplasma cultures of the joint from one bat were negative. Transmission electron microscopic examination of the affected joint capsule from one bat identified poxvirus particles in the cytoplasm of apparent synovial cells. Poxvirus DNA was isolated from the wing web and joint of one bat and preliminary phylogenetic studies indicate that the virus is distinct from any currently known poxvirus, but is distantly related to sheeppox, goatpox and lumpy skin disease pox. Poxvirus-induced bone lesions are apparently rare, and the histologic findings in these bats resemble those associated with the bone lesions induced by smallpox in children.1
1. Eeckels R, J. Vincent, V. Seynhaeve. Bone lesions due to smallpox. 1964. Arch. Dis. Childh. 39:591–597.