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19 May 1997
What is Wobbly Possum Disease?
WPD is a newly recognised disease of possums which is fatal in 95% of cases. Possums with the disease come out in daylight and are disoriented and uncoordinated, hence the name ‘wobbly' possum disease.
The 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, and to investigate its potential as a biological control for possums. The disease was suspected to be caused by a virus, and further research has been carried out to find out more about the disease and to isolate the virus.
The virus is transmitted directly from possum to possum, probably through faeces and urine. It cannot be spread through the air.
How long has WPD been 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 may have been present in this country for many years.
The Ministry of Agriculture will commission tests on historic possum samples stored in serum banks to try to determine how long it might have been here, but it is unlikely we will be able to establish this for certain.
It is also unlikely that we will ever be able to determine how it may have come here.
Why has research been carried out into WPD?
Possums are New Zealand's number one introduced animal pest. Not only do they destroy huge tracts of native bush, they are also be main vector for the spread of bovine tuberculosis in this country.
Currently, they are controlled by poisoning (mainly 1080), hunting and trapping, but there has been on-going research to try to find other means to reduce their numbers. The research into WPD was commissioned by MAF as part of this quest for new means to control possums.
Do other countries have WPD?
Australia is the only other country with significant numbers of possums (ie. Australian brushtail possums). In Australia, they are a native animal and protected in most states and territories. There have been no reports of possums in Australia suffering from WPD.
Do these results mean WPD and BDV are the same?
The tests results from Germany provide an initial indication that the viruses which cause the two diseases are alike, and are related antigenetically. This means that the immune system sees them as similar. However, this does not necessarily mean they are the same.
Further tests are being carried out to determine whether the WPD virus is in fact a Borna virus. These tests will involve complex research known as virus sequencing, which could take a year or more, and will be carried out in New Zealand and Germany.
If WPD is a Borna virus, what would this mean for New Zealand's international trade?
The Office International des Epizooties (the animal equivalent of the World Health Organisation) does not list BDV as a serious disease of animals, so it is likely to have little implication on trade in animals or animal products.
The most likely impact will be on trade in live animals, as there are currently few countries with restrictions on trade in animal products in relation to BDV. There could be costs associated with additional sanitary or medical requirements
The following current export certificates require New Zealand to declare freedom from Borna disease in live animals:
New Zealand exports possum meat to Hong Kong and Taiwan.Current certificates for possum meat do not require any certification for freedom from Borna disease.However, it should be assumed that importing countries may want to re-negotiate Import Health Standards prior to next trade.
What is Borna disease virus (BDV)?
BDV is a disease which occurs naturally in horses, sheep, cattle, ostriches and cats. It has also been transmitted experimentally to other mammals and birds in laboratory tests.
BDV causes various neurological disorders in effected animals, which vary depending on the type of animal.
For example, horses may initially show signs of anorexia, excessive salivation, chewing and frequent yawning, followed by loss of control of body movements, such as involuntary eye movements, head-pressing, sleepiness, partial paralysis, and loss of balance. Those horses which recover may be suffer from effects such as loss of coordination, blindness or fluid on the brain.
Is BDV a new virus?
Definitely not; BDV has been known overseas for at least 150 years.
Where is the BD virus found?
BDV is endemic in horse populations in Germany. It has also occurred in the Near East, other parts of Central Europe, the United States, Japan, Sweden, Israel and Syria.
However, not all infected animals show clinical signs. For example, the virus has been detected in about 30% of healthy horses in Japan. Some horses go through periods of apathy, energy loss and sleepiness before recovering completely. Infected cats can stagger and act depressed and apathetic before recovering on their own.
How does BDV spread?
BDV appears to be transmitted by close contact with infected animals and/or their excretions (e.g. urine and faeces). There are also indications that it may be spread in the animal's uterus to its offspring.
The virus is not transmitted by eggs, meat and meat products.
Can BDV be prevented or treated?
At this stage, there is no vaccine to prevent BDV, nor is there any effective treatment. However, the work carried out by AgResearch in isolating the WPD virus may assist in this if the two diseases are in fact related.
What happens in terms of animal health if WPD and BDV are the same?
Research will be carried out to determine whether other animals in New Zealand have the virus, and whether it is the less virulent strain, as found in United States and Japan, where animals which have the virus but do not show signs of serious illness.
Do other New Zealand animals have BDV?
At this stage, the virus causing wobbly possum disease is the only Borna disease-related virus that has been identified in New Zealand.
Tests for the disease have not previously been carried out, however, there have been no reports of animals with the clinical symptoms. New Zealand is in line with most other countries of the world in this respect; very few test their animal populations for BDV.
The Ministry of Agriculture will test to establish whether BD-related virus is present in any other animals. It is likely to focus on areas with a high incidence of wobbly possum disease.
Will New Zealand continue to investigate WPD as a possum control measure if it proves NOT to be BDV?
Yes. There is a definite need in New Zealand for a biological control for possums. WPD (if it proves not to be BDV) along with other viruses will continue to be investigated for this use, provided they have no side-effects on other animals or on humans.