Office of the Regional Executive for Biology - Central Region
 |
| About USGS / Science Topics / Maps, Products & Publications / Partnerships / Education / Newsroom / Jobs |
November 14, 2002
WNV: Despite colder weather in the north, WNV cases continue to occur. The first case in Washington state in equine has now been detected. This was a 14 year old horse, twice vaccinated, that developed disease 10 days after the second vaccination. Increasingly reports on the vaccine suggest a significant amount of time needs to pass after the second injection for effective immunity. Generally 4-5 weeks are used as guidelines. Some state veterinarians are recommending 6 month boosters in warmer climates with high mosquito exposure. This horse so far has survived, which may be reflective of partial immunity due to vaccination. This case means only Oregon, Idaho, Arizona, Utah, and Nevada have not yet reported cases originating in their state.
Overall, CDC shows a human case total of 3605 with 212 mortalities as of 11/14/02. The number of cases continues to mount, but the rate of increase has slowed considerably. USDA reports 13557 equine cases as of 11/12/02, which excludes the new Washington report. That total is an increase of 734 cases over the previous 9 days, also a bit of a decrease in case incidence.
CWD: A sixth deer farm in Wisconsin has been placed under quarantine since trace-backs from an initial positive farm have gone further. Farms have now been quarantined in Marathon County (1), Portage County (2), Walworth County (2) and Dane County (1). Only 2 farms so far have tested positive - one each in Walworth and Portage Counties.
The Mayo Clinic (Rochester, MN) has reviewed all 158 cases of CJD in their files and has found nothing that suggests a link to another TSE. However, HHS Secretary Thompson has authorized the use of $29M to fund studies on the transmissibility of scrapie and CWD to people. Below is a news report of a paper delivered by a neurologist, Dr. Bosque. He argues, and I agree with his assessment, that the possibility for transmission exists, but that any risk is very small.
On the diagnostic horizon, a commercial ELISA test has been approved for CWD detection in deer by the USDA. This, especially combined with automation on sample handling, will markedly increase the speed of sample processing and decrease the turnaround time. Next will be to look at the test reliability for elk.
Cases of CWD in Colorado range across the northern half of the state. I have previously provided locations of these as reported by Jeff Ver Steeg of the Colorado Division of Wildlife. The most recent cases are close to the Utah border, 28 miles north of Rangely, CO, and close to the Wyoming border in the northeast corner of Routt Co, CO.
Thomas J. Roffe, PhD, DVM
Northern Rocky Mountain Science Center
USGS-BRD
FWP Bldg, 1400 S. 19th Ave.
Bozeman, MT
T: 406-994-5789
F: 406-994-4090
Cell: 406-539-4955
Supporting Documents
National News : CWD Could Infect
Humans: Wasting Disease Would Be Hard to ID,
Scientist Warns
Date: October 19, 2002
Source: Rocky Mountain News
Contacts: Todd Hartman hartmant@RockyMountainNews .com or 303-892-5048
A new paper from a Denver neurologist suggests the possibility of humans contracting chronic wasting disease is underplayed and that the "most reasonable assumption" is CWD can be transmitted to some people. Patrick Bosque, an assistant professor at the University of Colorado School of Medicine, also wrote that scrapie - a CWD-like disease in sheep - can likely be transmitted to humans. Evidence to the contrary is "unconvincing," he said. Like many other researchers, Bosque said there is no known instance of a human infected by CWD, which fatally damages the brains of deer and elk via a rogue protein called a prion. But since prion diseases of any kind are so rare in humans, scientists might not be able to identify a CWD case were it to occur, he said. "It would be obvious by now if humans were highly susceptible to CWD," Bosque wrote, noting the disease has been present in wild deer and elk in northeastern Colorado for two decades or more without any reported cluster of a human version of the disease. Bosque's paper, published in Current Neurology and Neuroscience Reports, sounds a cautionary tone throughout and concludes that "practical measures to limit human exposure to animal prions, particularly CWD-infected deer and elk, should be improved." At the same, he said, the relative risk involved appears extremely small. As an example, he compared England's annual rate of mad cow disease in humans - a disease in the same family as CWD - with the rate of U.S. deaths to far more common food-borne illnesses, such as E. coli. The former is lower than one case in 2 million. The latter, about one in 50,000. Bosque, who earlier worked under Nobel Prize-winning prion researcher Stanley Prusiner, said that should CWD infect humans, the susceptibility rate would probably be similar to that of mad cow disease - that is, very low. So far, scientists believe 138 people have contracted the human version of mad cow even though millions were likely exposed to beef that might have carried the infectious prions. Medical experts had an advantage in recognizing mad cow in humans, Bosque said: Its victims were far younger than those who typically contract a rare, sporadic human version of the fatal prion illness called Creutzfeldt-Jakob disease, or CJD. In addition, the disease left a distinctive pattern in the brains of its victims. But should CWD affect humans, it might not leave the same clues as the human version of mad cow disease did, Bosque writes. "If, as appears to be the case with (mad cow)-to-human transmissions, only a small portion of the population is susceptible to CWD, then the association of disease with the consumption of venison might not be obvious." Bosque raises a similar point regarding scrapie: "It would be possible for a substantial proportion of cases of CJD to be caused by exposure to scrapie prions without this being epidemiologically apparent," he wrote. Bosque also questions the oft-cited notion that a so-called species barrier will prevent the transmission of CWD to humans. H calls the term misleading, saying the impregnability of such a barrier appears to depend on prion "strains," each of which exhibit different characteristics, and on differences in the prion's amino acid sequences. "People throw out the term species barrier," Bosque said in an interview. "It's a poorly understood concept and usually not absolute." In his paper he cited the example of goats, some breeds of which are more susceptible to sheep scrapie than are sheep. Bosque's paper comes at the height of hunting season in Colorado. Early indications suggest that most hunters aren't concerned about the disease, as only about one in five appears to be seeking to test their animals for CWD.
U.S. Department of the Interior | U.S. Geological Survey
URL: http://biology.usgs.gov/cro/WNV11-14-02.htm
Page Contact Information:
tlwilliams@usgs.gov
Page Last Modified:
