Office of the Regional Executive for Biology - Central Region
4-15-2002
Just back from 2 weeks travel, so here is a catch up on
happenings in the TSE world.
On CWD, most of you are aware of the Wisconsin outbreak and
the findings of 2 infected deer in Colorado west of the continental divide.
Along with the extremely high prevalences found in Nebraska deer these reports
are very worrisome. The disease in WTD seems to spread rapidly affecting a much
greater proportion of the population than either mule deer or elk. In Nebraska
final prevalence in the affected enclosure is 51% (79 of 154) (article #1). This
is extremely high. Wisconsin now has 12 infected deer found from a sample of 297
deer (4% prevalence) and tests are pending (article #2). Still no known source
for the Wisconsin outbreak which is thus far entirely in free-ranging WTD. They
have nearly reached their goal of 500 samples but many are backlogged at USDA's
National Veterinary Services Laboratory where the testing is done. Meanwhile,
Colorado is taking action to drastically reduce herds in the area where CWD was
found over the continental divide.
In Alberta, CWD was found in a game farmed elk during
surveillance at a slaughter plant (article #3). What makes this notable aside
from another piece of evidence of CWD's continued expansion, is that Alberta has
had a moratorium on importation of game farm cervids since the late 1980's.
Despite this, they still end up having the disease. Fortunately they also
maintain an intensive monitoring and surveillance system for CWD and likely
caught it early. Tracebacks are now in progress. No known source yet.
On the vCJD front, two pieces of news have come out (not
copied here because of the length of this update). A while back I forwarded an
article on finding abnormal prion protein in the muscles of mice from Stanley
Prusiner's lab (one of the foremost researchers on prion diseases). This
suggested that the infectious particle (whatever it is) may occur in muscle. In
France, however, detailed and repeated trials could not find abnormal prion
protein in cattle, sheep (with scrapie), goats and swine. So apparently the
murine muscle prion deposits are an aberration. The second report was a review
of death certificates in Britain to determine whether, as some think, vCJD isn't
really new that it was simply misdiagnosed in the past. If true it would suggest
vCJD is not derived from BSE (mad cow disease). A study involving 12091 deaths
for 1985-1995 has confirmed that vCJD is, in fact, a new disease entity
coincident with feeding BSE affected beef to humans.
Another report (article #4) on vCJD shows a doubling of
cases every 3 years. We still don't
know the incubation period in humans, but the report suggests 14 to 16 years
from infection to obvious disease. Taking that piece of information and applying
that to the constant questions about CWD – how confident are we that CWD
cannot be transmitted to humans? I guess we hang around for 14-16 years after
lots of people consume CWD-infected wildlife to get an answer. But, right now,
it is still accurate to say "CWD is not known to be transmitted to
humans".
Thomas J. Roffe, PhD, DVM
USGS-BRD
Northern Rocky Mountain Science Center
FWP Bldg, 1400 S. 19th Ave.
Bozeman, MT
T: 406-994-5789
F: 406-994-4090
Cell: 406-539-4955
Supporting
Documents:
Date: 31 Mar 2002
From: ProMED-mail <promed@promedmail.org>
Source: Rocky Mountain News, 30 Mar 2002 [edited]
http://www.rockymountainnews.com/drmn/state/article/0,1299,DRMN
_21_1059119,00.h tml>
Nebraska: Wasting illness hit 50% of herd
About half of the white-tailed deer within an 800-acre
enclosure in northwestern Nebraska have tested positive for chronic wasting
disease, a staggering total surpassing by far any known infection rate for the
deadly disease.
Though test results from the herd have trickled in for
months, the new numbers -- 79 positives out of 154 deer -- are nearly final,
pending a handful of additional lab results. They show a spread of the disease
unmatched outside of research pens in Fort Collins.
The numbers buttress emerging belief among scientists that
CWD is more contagious among white-tailed deer as opposed to mule deer and elk,
in which infection rates in the wild typically hover around 5% percent and1%,
respectively. It is especially alarming in Nebraska and points east,
where white-tailed deer herds are far denser than in Colorado.
The latest infection figures for the captive deer herd come
after Nebraska officials killed off the last of the animals 2 weeks ago to
prevent the disease's spread. CWD was first discovered within the herd in
November 2000. Since then, no live deer or elk have been permitted to enter or
leave the facility.
Bruce Morrison, overseeing the CWD control effort for
Nebraska's wildlife commission, said while the infection rate inside the pen is
very high, it has festered there for nearly 18 months -- plenty of time for it
to spread in a relatively confined space. "Our bigger concern is what could
be outside the pen, in the wild population," he said.
So far, it appears the disease hasn't moved as aggressively
in the rugged pinelands surrounding the captive herd. In a state-run hunt in
late January [2002], Nebraska biologists shot 113 wild deer within a 5-mile
radius of the enclosure, 9 of which tested positive.
Even better news arrived more recently, when Nebraska and
South Dakota workers teamed up to kill 183 animals along the border between the
states, and north of the enclosed herd. None of those animals were found with
CWD.
Date: 8 Apr 2002
From: Doug Metcalf <dmetcalf@boah.state.in.us>
Source: Wisconsin DNR News Release
MADISON, 5 Apr 2002 -- Efforts to sample and test 500
white-tailed deer from western Dane and Eastern Iowa counties continued today
with wildlife officials reporting they've received notification of 2 more
positive cases from the testing laboratory. This brings the total of known CWD-diseased
deer in the area to 12.
With the help of area landowners, wildlife managers are now
very close to finishing the job of collecting the 500 deer veterinary experts
determined were needed to present an accurate picture of the extent of the
disease in the surveillance area. The total number of
deer collected by the CWD Sampling Operations Center early
Friday morning was 471.
Wildlife health specialists are processing the tissue
samples rapidly and sending them off to a laboratory in Ames IA for testing. A
total of 272 samples have been tested.
The newest positive samples came from Sections 5 and 9 in
the Town of Vermont about 5 miles northwest of Mt. Horeb. Landowners have
provided most of the deer killed for testing.
More information can be found on the Chronic Wasting Disease
page on the DNR Web site:
<http://www.dnr.state.wi.us/org/land/wildlife/whealth/issues/CWD/>
Wisconsin Department of Natural Resources
PO Box 7921
Madison WI 53707
Date: 31 Mar 2002
Source: Alberta Agriculture, Food and Rural Development, 26
Mar
2002 [edited]
http://www.agric.gov.ab.ca/surveillance/cwd_update.html>
On 26 Mar 2002, the Canadian Food Inspection Agency (CFIA)
confirmed Chronic Wasting Disease (CWD) in a farmed elk from northern Alberta.
Brain from this animal was obtained as part of an ongoing voluntary surveillance
program for CWD, which is a joint initiative among Agri-Food Surveillance
Systems Branch, Livestock Diversification Branch, and the Alberta cervid
industry.
CWD is a reportable disease under the [Canadian] federal
Health of Animals Act, giving the CFIA authority to control any occurrences. The
CFIA has quarantined the affected elk farm and is working closely with Alberta
Agriculture Food and Rural Development to complete trace-outs of animals from
this farm.
Elk and deer with CWD may not show any visible symptoms of
the disease for several years. Eventually, as the disease becomes worse, animals
may exhibit loss of condition, excessive salivation, trouble swallowing,
difficulty in judging distance, and drooping ears. These symptoms are not
specific to CWD and can occur with other diseases as well. The only valid method
to diagnose CWD is by examining the brain tissue after the animal has died.
Specialized immuno-histochemistry (IHC) staining is the universally accepted
method of detection and is performed in the Agri-Food Surveillance Systems
Branch laboratory, with confirmation by CFIA.
CWD can pass from one animal to another and females can pass
it to their offspring, but the exact mode of spread has not been identified. CWD
was confirmed in over 200 farmed elk and 2 wild mule deer in Saskatchewan last
year. To control the spread of the disease, the CFIA has depopulated 7782 farmed
elk as of 22 Mar 2002. Owners of destroyed animals were eligible for compensation under the
provisions of the federal Health of Animals Act.
Alberta has had a moratorium on importing domestic elk and
deer since 1988. Since the Fall of 1996, Alberta has conducted CWD surveillance
on farmed and wild elk and deer in the province. As of 25 Mar 2002, testing of
3890 animals by IHC confirmed no evidence of
CWD. In the spring of 2001, Alberta Sustainable Resources Development
conducted a sampling of 199 deer in a 20-km wide swatch along the Alberta side
of the Alberta-Saskatchewan border north of Lloydminster. In addition, in the
Fall of 2000 and 2001, surveillance of wild elk and deer was enhanced in
wildlife management areas along Alberta's eastern border. All results have been
negative for CWD.
Date: Sun 31 Mar 2002
From: ProMED-mail <promed@promedmail.org>
Source: The Washington Post, Thu 28 Mar 2002 [edited]
http://www.washingtonpost.com/wp-dyn/articles/A28712-
2002Mar27.html>
Variant Creutzfeldt-Jakob Disease On Rise
The number of British cases of variant Creutzfeldt-Jakob
disease [abbreviated in ProMED-mail as vCJD or CJD (new var.)], the rare and
fatal human equivalent of "mad cow disease", is doubling every 3
years, even though measures to protect meat, the presumed source of the
infecting agent, have been in place for nearly a decade. The continued growth of the epidemic of vCJD almost certainly
reflects the long delay between infection and the appearance of symptoms, rather
than representing new infections, a British scientist told a gathering of
infectious disease specialists here.
"The trend is continuing upward," said Robert
Will, of the Western General Hospital, in Edinburgh, Scotland. "The central
issue is, how long is this going to go on? We don't know, because we simply
don't know what the incubation period is."
So far, 117 cases of vCJD have been diagnosed in Britain, 5
in France, one in Italy, and one in Ireland. The human disease was identified in
March 1996 (although 3 deaths from 1995 were subsequently ascribed to it). It is
characterized by widespread decomposition of brain tissue, giving the organ a
sponge-like appearance at the time of death. There is no treatment.
Most victims of "classical" Creutzfeldt-Jakob
disease die in their late sixties after developing relatively slow-onset
dementia. In the "variant" cases, mortality peaks in the late
twenties, and is often preceded by sudden behavior changes initially diagnosed
as psychiatric illness. The cause of both forms of CJD is thought to be an
abnormal form of a protein, called a prion. Unlike all other known infectious
agents, prions contain no genes, DNA, or other genetic material.
Classical CJD can arise spontaneously, or it can be acquired
as an infection. Cases have occurred after people have gotten tissue transplants
or brain-derived hormones from cadavers whose infections weren't apparent at the
time. In the case of vCJD, however, meat is the presumed source.
That is because, on the basis of both molecular and organ
damage, it appears to be identical to mad cow disease, whose formal name is
bovine spongiform encephalopathy (BSE). BSE was recognized in Britain in the
1980s. It was spread, in part, by feeding cattle with bone and protein
supplements that contained brain tissue from infected animals. That practice was stopped in 1988 in Britain. Since
then, many countries have taken many measures to keep nerve tissue out of feed
and meat.
No risk factors other than age and meat-eating have been
implicated, Will told scientists attending the International Conference on
Emerging Infectious Diseases. The disease isn't associated with social class,
occupation or previous surgery. Men and women are about equally affected. Travel
to Britain isn't necessary; 3 of the French victims, and the single Italian, had
never visited Britain.
British epidemiologists have identified 22 people who
received blood from vCJD victims and none has the disease or died of it, Will
said. Nevertheless, the Food and Drug Administration has asked that blood
collecting agencies in the United States not accept blood from people who spent
time in Britain in the 1980s.
A team of French researchers reported earlier in the
conference that its mathematical model of the British epidemic suggests the time
from infection to obvious disease is 14 to 16 years. The model predicts there
will be 267 cases, with an upper limit of 672.
Nearly 2 dozen European countries have found BSE, including
8 last year. The recent discovery of 3 BSE cases in Japan shows the disease
exists outside Europe. A method of assessing a country's risk of having BSE
cattle based on its past feed importation practices has proved quite accurate,
and Asian countries should now start using it, said Dagmar Heim, of the Swiss
Federal Veterinary Office.
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