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19 May 1997
After two years of study, New Zealand scientists researching 'wobbly possum disease' in the search for a possible biological control for possums have isolated and purified the virus which is it thought to cause it. They now have enough information to compare the new virus with known viruses, to see which it most closely resembles.
Wobbly possum disease was first diagnosed at the AgResearch possum colony at Invermay in early 1995. Further research was commissioned to identify the organism which caused it. The disease was suspected to be caused by a virus, and AgResearch has carried out further work to find out more about the disease and to attempt to isolate the virus.
Possums, which at present are the only animals in New Zealand known to be affected by wobbly possum disease, are a scourge in this country, spreading bovine Tb and threatening native forests. The need to find an effective control for them is a top priority in pest control.
Preliminary results from tests of blood samples carried out in New Zealand, Sweden and Germany indicate that the virus which causes wobbly possum disease may be like that which causes a disease known as Borna disease.
Research is continuing to identify the wobbly possum virus. It should be noted that just because viruses appear similar does not mean they are the same. The tests carried out so far are not able to determine if it is in fact Borna virus or not, and further tests are underway, both in New Zealand and overseas, to determine this. These tests may take a year or more.
While little is known about wobbly possum disease at this stage, more is known about Borna disease virus (BDV).
Borna disease has been known in overseas countries for more than 150 years. The virus causes neurological disorders in some animals and occurs naturally in horses, sheep, cattle, ostriches and cats. It has also been transmitted experimentally to other mammals and birds in laboratory tests.
It is endemic in horse populations in Germany and sporadic cases have been recorded in other countries, including Switzerland, Sweden and Israel. Not all animals show clinical signs of the disease; the virus has been detected in healthy horses in both Japan and the United States.
There is also still much to be learned about BDV and human disease. Research suggests BDV may be associated with disease in humans such as schizophrenia and affective disorder (manic depression). However, research has not shown conclusively whether BDV is simply found in association with human disease, or actually causes it, nor is it known how the virus is transmitted.
At this stage, the virus causing wobbly possum disease is the only Borna disease-like virus that has been been identified in New Zealand. It is not possible to determine precisely how long wobbly possum disease has been present in New Zealand, because appropriate tests have not been available, but anecdotal evidence of possums acting strangely suggests it may have been present in this country for many years.
The Ministry of Health advises people handling any animal, including possums, to follow standard hygiene procedures and make sure they wash their hands before eating, drinking or smoking, as is normal practice after handling any animal.
If owners of pets or stock believe their animals have become ill following contact with sick possums, they should take them to their vet and tell them of the exposure so the illness can be brought to the attention of MAF.
The Ministry of Agriculture is working to develop a test to establish whether this Borna disease-like virus is present in any other animals in New Zealand. It is likely to focus on areas with a high incidence of wobbly possum disease. It will also test historic possum samples stored in serum banks to try to determine how long it might have been here.
From the animal health perspective, the Office International des Epizooties (the animal equivalent of the World Health Organization) does not list BDV as a serious disease of animals and, if identified, is likely to have little implication on trade in animals or animal products.
If there is any impact, it may be on trade in live animals. There are few countries with restrictions on trade in animal products in relation to BDV. The exception may be the export of possum meat.
Media inquiries to:
Dr Barry O'Neil, Chief Veterinary Officer, Ministry of Agriculture (04)474 4128
Debbie Gee, Manager, Corporate Communications, Ministry of Agriculture (04)474 4258
Dr Gillian Durham, Director, Public Health, Ministry of Health (04)496 2115
Contact via Peter Abernethy, Senior Media Advisor, Ministry of Health (04)496 2202, pager (026)112 413