New Zealand’s surveillance
programme for
chronic wasting disease
Although we have very good evidence that deer and elk
populations in New Zealand have never been infected
with chronic wasting disease, consumer anxiety has
necessitated ongoing surveillance and monitoring to
satisfy markets of this country's freedom from the
disease. This article describes the deer industry, the
presentation and diagnosis of CWD, the surveillance
programme to investigate suspected cases and its
recent enhancements, and details of a recent
investigation of suspect cases.
The more than 4,000 farms in New Zealand that carry deer range
in size from smaller lifestyle properties to extensive stations. Deer
are generally farmed as part of a diversified livestock portfolio with
other species including sheep and cattle. Approximately 2.5 million
deer are farmed in New Zealand, around 50% of the world’s
farmed deer population. Split roughly 45% in the North Island and
55% in the South Island, there are an estimated 1.7 million female
deer and 800,000 males. These farms are serviced by approximately
with most animals surviving from a few weeks to three to four
190 of the 1,304 veterinarians engaged in private practice,
months. While protracted clinical disease is typical, sudden death
according to a 2002 survey(1) conducted by the Veterinary Council
occurs occasionally. The diagnostic method used in New Zealand is
of New Zealand.
histopathologic examination of brain tissue. The Prionics western
Chronic wasting disease
blot test is another diagnostic tool added recently, but is still
Chronic wasting disease (CWD) is a progressive, fatal neurological
disease of deer and elk in North America. It is a transmissible
spongiform encephalopathy (TSE), a family of diseases reported in
a number of species, the pathology of which is attributed to the
proliferation of an altered form of a normal intracellular protein,
undergoing validation trials. When fully validated, it will be
employed as either a primary diagnostic tool, for slaughterhouse
samples, or as a secondary test when samples from field
investigations are either missing critical sites for examination, or
the degree of autolysis prohibits the use of histopathology.
known as PrP. Unlike BSE in cattle or FSE in cats, CWD is
Surveillance programme
contagious. The most striking clinical features of CWD are loss of
Since the beginning of 1990, MAF has maintained a continuous
body condition and changes in behaviour. Affected animals may
CWD surveillance and monitoring programme to support
increase or decrease their interaction with handlers or other
international acceptance of our CWD-free status. The programme
members of the herd. As the disease progresses, affected animals
involves the following components:
may become difficult to handle through the yards. They may show
repetitive behaviours such as pacing, periods of somnolence or
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a CWD awareness campaign amongst veterinary practitioners
and deer farmers;
depression from which they are easily roused, or may carry their
head and ears lowered. Affected animals continue to eat but their
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CWD, along with all other TSEs, has been notifiable since 1993;
consumption decreases leading to gradual loss of body condition.
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a toll free phone number to report any cases of suspected exotic
In later stages many animals display excessive drinking and
urination, increased salivation with resultant slobbering or
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the National Centre for Disease Investigation;
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a network of MAF-approved veterinary diagnostic laboratories;
and wide based stance.
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MAF’s Expert Veterinary Pathologist;
Death is inevitable.
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referral of samples from CWD investigations, when necessary,
drooling (refer Figure 1) and incoordination, particularly posterior
ataxia, fine head tremors,
In North American herds
Figure 1: An elk affected with
chronic wasting disease
(Photo courtesy of Dr Elizabeth S
Williams, University of Wyoming).
disease;
to international experts overseas.
experiencing CWD for the first
Awareness campaign
time, sporadic cases of prime
Veterinarians engaged in deer practice have been alerted to the
aged animals losing condition
possibility of CWD cases through regular MAF circulars. The
and not responding to
purpose of these is to remind veterinarians about the nature and
symptomatic treatment, and
significance of CWD, and their responsibility to be vigilant for signs
death from pneumonia, are commonly reported. Aspiration
that might be the first indication of its presence in New Zealand. In
pneumonia, presumably from difficulty swallowing and
addition to circulars, articles about CWD have been published from
hypersalivation, may lead to misdiagnosis of the condition if the
time to time in Vetscript, the monthly magazine sent to all 1,523
brain is not examined.
members of the New Zealand Veterinary Association.
Most cases of CWD are seen in animals three to seven years old,
Deer farmer awareness has been promoted through industry
although it has been seen in animals as young as 17 months and as
publications, which describe in layman’s terms the clinical signs of
old as 15 years. The clinical course varies from a few days to a year,
CWD, and the joint incentive programmes by MAF and the deer
Surveillance 29(4) 2002
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industry (see below) that encourage investigation of any suspicious
These include the obligation for a veterinary laboratory
cases. This information is also publicly available on the MAF
diagnostician to read, within one working day of specimens being
website: www.maf.govt.nz/tse
submitted, the clinical histories of all sick farmed animal cases to
Notifiable disease toll free
telephone line
exclude the possibility of an exotic disease. If an exotic disease is
suspected, the diagnostician must notify the NCDI on the same day
as the provisional diagnosis is made.
CWD is notifiable under the Biosecurity Act 1993. Any person
suspecting CWD must notify MAF. To facilitate reporting of
Another requirement critical to CWD surveillance is that all brains
suspected exotic disease MAF has established its Exotic Disease and
received as part of these routine submissions must be screened, in
Pest Emergency freephone, which operates 24 hours a day, seven
accordance with the diagnostic techniques described in the
days a week. The service has been well publicised and receives, on
standard, for any evidence of the TSEs. This requirement applies
average, 70 calls a month specifically related to animal disease.
even if the case does not have a clinical history of nervous disease.
These are referred to the National Centre for Disease Investigation.
All cases in which a TSE cannot be ruled out must be referred for a
second opinion to MAF’s Expert Veterinary Pathologist
National Centre for
Disease Investigation
The National Centre for Disease Investigation (NCDI), which was
(see below).
Financial incentives
established by MAF in November 1998 (refer Figure 2), integrates
MAF provides financial incentives to veterinary practitioners to
the functions of the Exotic Disease Response Centre (EDRC) and
encourage submission, for laboratory examination, of brains (or
the New Zealand Animal Health Reference Laboratory (NZAHRL).
heads) from appropriate cases of disease in cervids. The case
The EDRC has a team of seven veterinary epidemiologists whose
definition that qualifies for incentive payments has recently been
main responsibility is to conduct field investigations of suspected
widened, and includes, subject to specific criteria being met,
exotic diseases. The laboratory support for investigations is
wasting, nervous disease, and acute pneumonia.
provided through the NZAHRL, which has a medium and high
MAF pays the following incentives directly to farmers
security laboratory (physical containment levels 2 and 3,
and veterinarians:
respectively(2)). The NZAHRL is staffed by 14 veterinary
diagnosticians, 22 technicians and support staff, and three staff
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case that meets the sampling criteria below. (The deer industry
dedicated to quality assurance, and during the year 2000 achieved
has agreed to fund this portion of the incentive payments up to
third party accreditation to ISO 17025(3).
Approved diagnostic laboratories
the first 300 brains per annum.)
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For the routine investigation and reporting of disease cases from
farmed animals, MAF has approved a network of six privately
developed the Standard for MAF Biosecurity Authority Approved
Veterinary Diagnostic Laboratories, which outlines the operational
$100 to the veterinarian for each submission of appropriate
samples and a submission form;
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owned veterinary diagnostic laboratories (refer Figure 2). To ensure
that the information supplied is of a credible standard, MAF has
$100 to the farmer for contacting the veterinarian about each
an additional payment of $60 to the veterinarian for each case
if he/she removes the brain on site.
The sampling criteria are:
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progressive non-responsive nervous disease or illthrift cases in
adult (ie older than two years) cervids,
and technical requirements that approved laboratories must meet.
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acute or peracute pneumonia or aspiration pneumonia in adult
(ie older than two years) cervids,
in each case, where no other cause of the disease can be definitely
diagnosed at the time of necropsy.
MAF also pays the laboratory for histopathological examination of
the tissues and removal of the brain (if required).
Expert veterinary pathologist
MAF provides the services of an Expert Veterinary Pathologist, Dr
Alastair Johnstone, who is based at the Pathobiology Section,
Institute of Veterinary, Animal and Biomedical Sciences, Massey
University. This service is offered, free of charge, to all approved
veterinary diagnostic laboratories when they wish to obtain an
Figure 2: Location of Approved Veterinary Diagnostic Laboratories in
New Zealand.
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independent second opinion on any sick farmed animal case.
MAF’s technical and operational requirements for the expert are
Surveillance 29(4) 2002
specified in the Surveillance Standard for the MAF Biosecurity Expert
However, because of issues of sample quality and the validation
Veterinary Pathologist.
process the Prionics test is still undergoing in cervids, the fixed
If there is a case that requires further testing in order to confirm or
rule out the disease in question, the Expert Pathologist sends the
samples to the NCDI for referral overseas to the appropriate
reference laboratory.
Recent enhancements
samples of the brains were referred overseas for
immunohistochemistry. The Neuropathology Department of the
Veterinary Laboratories Agency, Weybridge, United Kingdom,
performed the testing using monoclonal antibodies F89 and R145.
The tests revealed no evidence of CWD.
A week after this investigation began, the same farmer contacted his
MAF is currently trialling the sampling and testing of cervids that
veterinarian concerning two more elk showing signs of illthrift. The
have been either condemned at antemortem inspection or found
veterinarian euthanased both animals, an 18-year-old imported
dead in the slaughterhouse stockyards. Samples of brain tissue from
purebred and a four-year-old crossbred, and samples were sent to
these animals are collected by MAF veterinarians and sent to the
the approved veterinary diagnostic laboratory used previously.
NCDI for testing, using the Prionics western blot method. This test
Histopathological examination of samples did not support
is still undergoing validation in cervids, both in New Zealand and
diagnosis of CWD in either elk. A morphologic diagnosis of
abroad, but will be the preferred method for slaughterhouse
granulomatous enteritis and lymphadenitis, compatible with either
surveillance once the validation process has been completed.
Johne’s disease or avian tuberculosis, was made in the younger
Recent investigation
animal. Johne’s disease was confirmed by culture. The samples from
In August 2002, a deer farmer in the South Island contacted a
veterinary practitioner about some elk showing signs of illthrift.
During his initial visit to the property the veterinarian examined
two animals. A two-year-old male crossbred elk in poor body
condition had deteriorated over a period of two to three months.
the 18-year-old elk were referred to the Expert Veterinary
Pathologist for a second opinion because of its history of
importation. The Expert Pathologist ruled out CWD. Once again
the hepatic changes supported a diagnosis of chronic degenerative
hepatopathy, suggestive of pyrrolizidine alkaloid toxicosis.
The farmer had not observed any neurological signs. A postmortem
Summary
examination found severe generalised muscle atrophy and some
MAF’s surveillance system for CWD employs a surveillance strategy
lung consolidation. The other animal examined, a female purebred,
based on:
approximately 18 years old, had been imported from Saskatchewan,
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veterinary and farmer awareness,
prolonged scouring and severe muscle wasting. Postmortem
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a legal obligation to notify MAF if CWD is suspected,
examination confirmed generalised muscle atrophy.
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a toll free number and financial incentives to facilitate disease
Canada, in 1984. She was in poor body condition, with evidence of
investigations,
Samples of liver, kidney, abomasum, duodenum, fresh and fixed
brain, from both animals were sent to a MAF approved veterinary
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standardised laboratory diagnostic techniques,
diagnostic laboratory. After initial histopathological examination at
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independent expert advice, and
the laboratory, the samples were referred to the Expert Veterinary
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referral of cases overseas when required.
Pathologist because:
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MAF will carry on with the review and enhancement of its
scattered vacuolar change, of antemortem origin, was present in
surveillance system to ensure that New Zealand can continue to
both brains, and
state with confidence that its cervids are not infected with CWD.
Canadian officials notified MAF in 2001 that, subsequent to the
exportation of the female elk in 1984, CWD has been diagnosed
in the herd of origin in Saskatchewan.
The Expert Veterinary Pathologist reported that there was little to
support the suspicion of CWD. The hepatic changes supported a
References
(1) Newsbrief, Veterinary Council of New Zealand, June 2002, p 4.
(2) Australian/New Zealand Standard Safety in Laboratories. Part 3
Microbiological aspects and containment facilities AS/NZS 2243.3 2002.
(3) ISO Guide 17025 - General requirements for the competence of testing and
calibration laboratories (Reference number NZS/ISO/IEC17025:1999).
diagnosis of chronic degenerative hepatopathy, highly suggestive of
Roger Poland
pyrrolizidine alkaloid toxicosis, which could explain the
Programme Coordinator, Surveillance
antemortem spongiotic changes present.
MAF Biosecurity Authority
The Prionics western blot test conducted by the NCDI gave
Wellington
negative results on the samples of fresh brain from both animals.
Email: polandr@maf.govt.nz
Surveillance 29(4) 2002
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