Germ war on rabbits

From ANIMAL PEOPLE, October 1997:

Frustrated by governmental caution, farmers in
at least six districts of the South Island of New
Zealand separately introduced the deadly rabbit
calicivirus in late August. Their evident strategy
was to goad the government into undertaking
large-scale deliberate releases, as Australia
did in October 1996, a year after an accidental
release from a test site on Wardang Island
turned four of the six Australian states into––in
effect––a germ warfare experiment.
Concerned about liability, New
Zealand authorities held back a long discussed
release. On the verge of the rabbit birthing season,
highland farmers finally forced the issue
by importing from Australia the internal organs
of rabbits who had died of calicivirus, pureeing
the organs in blenders with bait such as oats,
jam, or carrots, and pouring the mess around
rabbit warrens.

“Half to two-thirds of of the rabbitprone
limestone country north of Christchurch
was laid with the contaminated bait,” the New
Zealand Press Association reported on
September 18. “Land further north, between
the Waipara and Hurunui ivers, also appeared
to be well-covered.”
Rabbit calicivirus was said to be
killing 95% of the rabbits who came into direct
contact with it. The disease induces internal
hemorrhage, causing death within 30 to 40
hours of exposure in most cases.
“The timing was perfect,” said
Muller Station farmer Stephen Satterthwaite,
whose farm reportedly spent $200,000 on conventional
rabbit killing methods over the past
two years. “Rabbits are breeding, but have not
yet produced their litters. Almost all the dead
female rabbits we find are pregnant.”
There were indications that the New
Zealand government set up the “unauthorized”
release on purpose. According to the NZPA,
“Farmers were first given clues in 1991 on how
to manufacture the rabbit calicivirus inoculant
by the Ministry of Agriculture’s semi-arid lands
group at Lincoln, in a ‘rabbit managers’ fact
pack.’ They were told that the livers and
spleens of rabbits infected with the virus could
be put through a blender, and if a vaccine was
required to protect domestic rabbits, the inoculant
could be inactivated with formalin.”
After the release, New Zealand
biosecurity minister Simon Upton said the federal
Biosecurity Act would be amended to
legalize possession of rabbit calicivirus. But
the New Zealand cabinet opted not to import
stocks of the virus it has stored in Australia.
Waikanae farmer Ron Trotter touted
rabbit calicivirus as the safest possible response
to rabbit numbers which had apparently rapidly
increased over the past four to five years. “We
don’t want to lay down poison with so many
household cats and dogs nearby, not to mention
youngsters,” he said. “The virus is the only
practical way to eliminate the problem.”

Timaru region farmer Philip Mackay
compared the impact of rabbit calicivirus
favorably to that of poisoning. “When 1080
has been dropped on the land, there’s a total
absence of life,” Mackay said after viewing
the Timaru highlands from a helicopter. “It’s
quite different today. There were lots of birds
about. It looks to be totally species-specific.”
Otago Regional Council chief executive
Graeme Martin called a Resource
Management Act requirement that government
consent be obtained for aerial distribution of
rabbit calicivirus-laced bait “pedantic and
unwarranted. The environmental effect of
baits falling into a waterway is negligible by
comparison with natural events that will occur
from afflicted rabbits,” Martin said.
But Canterbury Regional Council
chair Richard Johnson urged caution, as
reports emerged that transmission from rabbit
to rabbit was not occurring as rapidly as
expected. “If we’re not careful,” Johnson
speculated, “we’ll end up making a whole lot
of rabbits immune to it.”
Ministry of Agriculture chief veterinarian
Barry O’Neill warned that this is just
what would happen if farmers mixed baits with
water of the wrong alkalinity level.

Human health threat
Rabbits were introduced to both
Australia and New Zealand for hunting purposes
circa 1850. In both nations they soon
outcompeted native marsupials, took advantage
of the extirpation of predators by sheep
farmers, and have challenged sheep for use of
forage ever since.
Competition from rabbits has also
been blamed for the decline of various native
species. The 1950 introduction of the fleaborne
rabbit disease myxomiatosis knocked
down rabbit populations for a time, but surviving
rabbits have propagated resistance to
myxomiatosis, touching off a long quest for
another biological response.
As farmers across New Zealand
rejoiced that rabbit calivirus was on the loose,
and clamored to have it spread faster, and the
Agriculture Ministry insisted that the disease
has been present in 43 nations for 13 years
without harming humans, Christchurch epidemiologist
Neil Cherry told media that a reexamination
of Australian data which purported
to show the release there last year had no
effect on humans actually found the opposite.
Reported NZPA, “Dr. Cherry found
that the incidence of illness in part of the study
had not been seasonally adjusted to allow a
uniform rate to be measured. Once the adjustment
was made,” which essentially takes into
account fluctuations found in rates of exposure
to most contagious diseases, “the rate of sickness
doubled, and those exposed more frequently
had a greater risk of disease.”
Among Cherry’s numbers:

Symptoms   Exposed  Highly      Non-
of illness      persons  exposed   exposed
Gastrointestinal 6% 8% 3%
Fever & flu 18% 19% 6%
Rashes .7% .7% .4%
Hepatitis .3% .1% .0%
Haemological .7% 1.6% .5%
TOTAL ILLNESS 11% 13% 4%

Said Cherry, “My professional conclusion
is that there is evidence of health risk
to humans, unproven but now statistically relevant.
I would urge all farmers and their families
to be careful, and that the Health Ministry
start monitoring their health.”
In March 1997, objecting to early
release of rabbit calicivirus, the Health
Ministry argued that the disease should undergo
the same level of safety testing as vaccines
and drugs intended for human use. “While the
introduction of the rabbit calicivirus appears to
pose low risk to human health,” the ministry
said in a position paper, “it is unable to be
quantified at present, given the lack of knowledge
of the biology of transmission.”
A further biological peril, warned
Landcare Research predator expert Grant
Norbury, is that feral ferrets who carry
endemic bovine tuberculosis could respond to
an abruptly reduced rabbit population by dispersing,
spreading TB to new areas. Norbury
poisoned 77% of the rabbits in one test location
with Compound 1080 during a recent twoyear
trial, and poisoned 99% in the other.
Radio collars attached to the collars of 70 ferrets
and 28 cats found in the two locations
found that each ferret maintained a home range
of about 90 hectares and each cat maintained a
home range of about 224 hectares prior to the
poisoning. After the 77% rabbit poisoning,
the ferret and cat ranges remained about the
same––but after the 99% poisoning, the ferrets
tripled their ranges, and some cats wandered
up to six miles outside their former territory.
The cat diet remained about as it was
at any level of poisoning, Norbury found, but
ferrets ate far more native skinks, geckos, and
insects, as well as introduced bird species,
hedgehogs, and mice. Few ferrets starved.
Their fecundity dropped, however, resulting
in a declining population over time.
Conservation Minister Nick Smith
budgeted $572,000 for predator trapping to
protect native species including the highly
endangered black stilt, wrybills, terns, and
dotterels in 15 areas where the rabbit calicivirus
had been released, but vetoed a Forest
and Bird Society demand that the amount
should be increased fourfold to sixfold.
On August 23, just days before rabbit
calicivirus was discovered at large in New
Zealand, Sydney Morning Herald agricultural
editor Anthony Hoy warned that, “Nature
appears to be winning the war against rabbit
calicivirus in the high rainfall areas of
Australia,” taking advantage of lush vegetation
to outbreed the spread of the disease, “but
in arid and semi-arid test sites,” Hoy continued,
“where rabbit calicivirus mortality is as
high as 95%, feral cats and foxes, deprived of
their traditional prey, are decimating native
animals and birds.”
Hoy’s pessimism contrasted with the
verdict of Sydney Morning Herald c o l l e a g u e
Greg Roberts as of April 5. Then, Roberts
wrote, “For the first time in almost 20 years,
the red sand dunes of the Simpson Desert have
come to life. The spinifex, cane grass, and
other plants of the dune ridges are thriving.
Their inhaibtants, including the endangered
Eyrean grasswren and a host of small marsupials,
are multiplying. Unusually heavy rains
earlier this year helped, but before the rabbit
calicivirus reached the desert last September,
a fragile new bud emerging on the dunes was
promptly cropped by voracious rabbits.” But
Roberts noted that the renewed growth was
encouraging ranchers to put cattle out on the
desert for the first time in 15 years––a new
threat to rejuvenation and native wildlife.
New Zealand veterinarians reported
they could barely keep up with the unanticipated
demand for vaccination of pet rabbits
against the calicivirus, at prices of from $21 to
$28 apiece. “I didn’t realize there were that
many pet rabbits,” DVM Tony Mitchell of
Merivale told The Christchurch Press.
But longtime anti-rabbit crusader
Allan Innes, who organized attacks with
arsenic and 1080 more than 20 years ago,
urged the dispatch of teams with guns, gas,
dogs, and traps to exterminate any rabbits in
New Zealand who survived the calicivirus.
Concern about the humaneness of
rabbit calicivirus appeared in a public opinion
poll on response to rabbit proliferation done
last winter by Landcare Research staffers
Roger Wilkinson and Gerald Fitzgerald.
Of 600 New Zealanders, 76% considered
shooting rabbits acceptable; 47% considered
trapping acceptable; 42% considered
rabbit calicivirus release acceptable; and just
24% considered poisoning acceptable. Only
35% favored the deliberate release of rabbit
New Zealand has been spending $35
million a year on rabbit control, blaming rabbits
for $50 million annually in lost agricultural
Brushy-tailed possums
While a record 23,949 rabbits were
the main targets of the Easter Bunny Shoot on
April 1 in Central Otago, some of the 500 participants
also won points for killing 117
brushy-tailed possums, 19 hares, 14 goats,
and 96 miscellaneous feral predators, including
cats, ferrets, and stoats. The New
Zealand government, farmers, and conservationists
would like to extirpate them all––and
after rabbits, none more than the possums.
The most aggressive possum-hater in New
Zealand may be Green Party co-leader Ron
Donald. Campaigning to designate possum fur
“ecofur,” Donald has reportedly covered his
seat in Parliament with possum fur, and wears
a possum fur tie to Parliamentary sessions.
Native to Australia, where they are a
threatened arboreal species, brushy-tailed possums
were imported to New Zealand and
released by fur trappers early in the 20th century.
Having no natural predators in New
Zealand, they took to ground-dwelling, and
multiplied up to an estimated 70 to 100 million,
at the presumed expense of native
wildlife. Cattle ranchers hate them because,
like ferrets, they carry endemic bovine TB.
Brushy-tailed possums were already considered
a nuisance by the government when, as
fur prices soared in 1975, trappers distributed
more to parts of New Zealand that didn’t
already have them.
Competing for possum-killing contracts
is now big business. Feral Control Inc.,
for instance, reportedly spent $4 million in the
four-year effort to develop Feratox, an encapsulated
form of cinnamon-flavored cyanide
that the notoriously trap-shy and bait-shy possums
supposedly will ingest without suspicion.
Field trials cosponsored by the Animal Health
Board, and the Foundation for Research,
Science, and Technology began in August.
Try schizophrenia?
Compound 1080 was favored for
possum-killing until last year, when possum
poisoning by Environment Wikato in the
Rangitoto Ranges, using carrot bait, was
found to be killing native robins, tomtits, pet
dogs, and cattle. The New Zealand Animal
Health Board in November 1996 banned the
use of carrot bait, to protect native birds––but
that made 1080 much less attractive to the possums,
too. Organizing as the Possum Bounty
Group, 6,500 trappers spent the winter and
spring campaigning unsuccessfully for the
restoration of possum bounties that were in
effect 1951-1961. The bounties were eventually
cancelled because instead of killing possums
in sensitive but remote areas, trappers
tended to “farm” them wherever convenient.
As enthusiasm for rabbit calicivirus
swept rural New Zealand, a hue and cry arose
for the intentional release of another disorder,
“wobbly possum disease.” Already at large,
the disease was discovered in 1995. It appears
to be a variant of borna disease, common in
horses, sheep, cattle, ostriches, and cats.
The disease produces generally nonfatal neurological
disorders, with symptoms resembling
those of rabies, but researchers hoped when it
was first isolated that it could be cultivated
into a lethal form.
However, German investigators in
1996 recovered the borna virus from two
human patients who were suffering from
manic depression, one with chronic-obsessive
compulsive disorder, and one with major
depression and chronic fatigue syndrome.
Borna disease is also tentatively linked to

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