A neurological syndrome in a free-living population of possums (Trichosurus vulpecula)

AIMS: To determine the clinical and pathological features of a neurological disease syndrome in a free-living possum population in New Zealand and to compare this syndrome with wobbly possum disease. METHODS: An outbreak of a neurological disease in possums in the Rotorua district was investigated in 1994. A variety of tissues was collected and investigated microbiologically and histopathologically. Tissues stored from clinically affected possums were homogenised, clarified and inoculated into healthy possums by the intra-peritoneal route. The clinical signs and histopathological lesions in naturally-infected and in experimentally-inoculated possums were assessed and compared with those of possums affected with wobbly possum disease. RESULTS: Histopathological investigation of three of the naturally-affected possums revealed non-suppurative encephalitis with perivascular cuffing, diffuse non-suppurative meningitis and focal non-suppurative myocarditis. These lesions were suggestive of a viral infection. No pathogenic bacteria were recovered and no viruses were isolated in tissue culture. A neurological disease, indistinguishable from wobbly possum disease, was reproduced in five out of the eight experimentally inoculated possums. In two experimental cases the clinical signs were very mild and, in most cases of the natural and experimental disease, histopathological lesions in the central nervous system were mild in comparison with wobbly possum disease. Possums which did not develop clinical signs of neurological disease or have lesions in the central nervous system did have infiltrations of mononuclear inflammatory cells in the liver and kidney. CONCLUSIONS: This neurological disease, reported for the first time in a free-living population, closely resembles and may be the same as wobbly possum disease. The milder nature of this disease could suggest there may be more than one strain of the aetiological agent.