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Wanted: Wobbly Possums

AgResearch Invermay researchers have discovered a new fatal disease of possums. Research is still at a very early stage, but scientists are excited about the potential of the disease as a weapon to reduce possum numbers in the wild. Investigations will continue during the next year.

The disease, given the name "Wobbly Possum Syndrome", was discovered accidentally in a possum captured on the Taieri Plains. Invermay researcher Dr Colin Mackintosh says it appears to have been occurring naturally in feral possums around the Taieri.

Invermay has a colony of possums, used for research by Dr Bernie McLeod, who hopes to develop a control method by interfering with possum reproduction. PhD student Janet Crawford noticed one of the colony's possums acting unusually, and then discovered the disease had spread to other animals in the large pen. The worst affected animal was killed, and a post-mortem examination revealed a pattern of lesions which had never been described before.

Three healthy possums were added to the pen and all developed signs after about three weeks. Subsequent laboratory analysis has indicated the disease is caused by an unidentified virus, and workers at AgResearch Wallaceville and Massey University are working hard to culture it.

Symptoms of Wobbly Possum Syndrome include uncoordination, head tremors or "bobbing", and feeding during the day. It also seems to cause blindness. Initial signs are subtle, with vague signs of dullness and a slightly raised head, but as the disease progresses over a period of six weeks, the possum becomes weak, sleeps on the ground, and is uninterested in its surroundings.

Since reporting the discovery, Mackintosh and McLeod have received many calls from people who believe they may have seen affected possums. A high proportion have come from the North Island's East Coast down to the Bay of Plenty, and researchers are particularly interested in these reports.

Anecdotal reports refer to sightings of wobbly possums as far back as 15 years ago, though there is no way of verifying if the disease was responsible. One element of confusion facing investigators is that many possums die off during winter normally, and weakened animals may be mistaken for those that are actually infected.

Mackintosh has no idea how widespread the virus is, how it is spread in the wild, or how effective it is, but he's keen to find out and is interested in hearing from anyone in New Zealand who has seen such symptoms in possums.

It is possible that the disease occurs in pockets rather than appearing throughout the country, possibly affecting possums in places where they are particularly common.

"It's far too early to suggest we have discovered a new possum control method, but we're very pleased to have discovered the first agent that seems to be able to consistently kill possums," he says.