After two years of study, New Zealand scientists researching 'wobbly possum
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
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
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
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
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
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
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
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
If WPD is a Borna virus, what would this mean for New Zealand's
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
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
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
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
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