Dale A. Smith1, DVM, DVSc; Cathy M. Shilton1, BSc, DVM; Leslie W. Woods2, DVM, PhD
On 9 August 1998, a 1-mo-old moose calf, born at the Toronto Zoo, became acutely and severely ill. Omphalophlebitis and abscess were identified and surgical debridement of the lesion was attempted, but the animal died. On gross post-mortem, widespread hemorrhages and severe hemorrhagic typhlocolitis were present as well as a hepatic abscess associated with the infected umbilicus. Microscopically, there was widespread vasculitis and thrombosis, particularly in the gastrointestinal tract. Amphophilic, intranuclear inclusions were present in many endothelial cells, suggestive of adenoviral infection. On 14 August 1998, a 2-mo-old moose calf, also born at the Toronto Zoo, became acutely sick and died. Major post-mortem findings were severe hemorrhagic typhlocolitis and moderate chronic bronchopneumonia. Microscopic vascular lesions were similar to findings in the calf, which had died 5 days earlier.
Immunoperoxidase staining for bovine adenovirus type 5 was positive on tissues from both calves. Transmission electron microscopy revealed adenovirus particles within endothelial cell nuclei of both calves. Virus isolation using tissues from both calves was attempted in primary bovine spleen, equine ovary and rabbit kidney cell lines. No virus was isolated from either case following five passages over a period of 5 wk.
Three additional cases in moose calves were identified upon review of the post-mortem results of 29 moose which had died at the Toronto Zoo since 1974 (13 calves, 3 juveniles, and 13 adults). These calves, approximately 2 wk of age, had died over a 10-day period in 1985. Two of the calves were orphaned wild moose; the third was born at the Toronto Zoo but had been orphaned at 6 days of age when its mother died of severe necrotizing typhlocolitis. The major post-mortem finding in all three calves was severe multisystemic vasculitis and thrombosis, with amphophilic intranuclear inclusions in endothelial cells.
Adenoviruses are non-enveloped, highly host specific, DNA viruses. Infection is usually systemic, with strains of the virus having tropisms for the respiratory and alimentary tracts, vascular endothelial cells or hepatocytes. Typically, adenoviruses cause mild or subclinical respiratory or enteric infections, with clinical disease only in young or immunosuppressed individuals. In domestic cattle, there are 10 serotypes of the virus. Many strains can be isolated from normal cattle. Enteric infections have been described sporadically in 1–8-wk-old calves and feedlot animals. Post-mortem findings in affected calves include vasculitis, endothelial intranuclear inclusions, and widespread thrombosis.1
In 1996, an outbreak of adenoviral disease occurred in wild mule and black-tailed deer in Northern California.2 The main post-mortem lesions included severe pulmonary edema and hemorrhagic enteritis, with widespread vasculitis and thrombosis. Intranuclear inclusions were prominent in endothelial cells. A diagnosis was made based on electron microscopic demonstration of adenoviral particles in endothelial cells, fluorescent antibody and immunohistochemistry using antibody to bovine adenovirus type 5 and virus isolation in deer pulmonary artery endothelial cells.
This is the first report of the infection of moose by an adenovirus, and of the presence of adenoviral disease in a cervid in Canada.
1. Barker, I.K., A.A. Van Dreumel, and N. Palmer. 1993. The alimentary system. In: K.V.F. Jubb, P.C. Kennedy and N. Palmer (eds). Pathology of Domestic Animals. 4th ed., Academic Press, San Diego, CA. Pp. 1–317.
2. Woods, L.W., P.K. Swift, B.C. Barr, M.C. Horzinek, R.W. Nordhausen, M.H. Stillian, J.F. Patton, M.N. Oliver, K.R. Jones, and N.J. MacLachlan. 1996. Systemic adenovirus infection associated with high mortality in mule deer (Odocoileus hemionus) in California. Vet. Pathol. 33:125–132.