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Media Release |
19 May 1997
Wobbly Possum Disease/Borna Disease Virus Background
Information
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.
How is WPD spread?
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:
llama and alpacas to the United Kingdom
sheep and goats to China
goats to Uruguay
horses to South Africa
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.
