Volume 4, Number 37 - December 9, 2004
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Elk Feedgrounds in Wyoming - Part 3
The practice of providing supplemental feed for elk in the winter has been the center of countless working groups, public forums, media stories and street corner debates. The Wyoming Game and Fish Department has been at the center of elk feedgrounds since their inception. WG&F recently released a new report called "Elk Feedgrounds in Wyoming." It was written by WG&F veterinarians, biologists, wardens, and compiled by Jackson's Regional Information and Education Specialist Mark Gocke.
"This was not intended to be a lengthy discussion on elk feedgrounds, but instead a description of the most important aspects of feedgrounds," Gocke said. "The purpose was simply to provide factual information on the many different facets of elk feedgrounds."
Artificial feeding of wildlife, be it birds or bison, is a two-edged sword. Most wildlife disease professionals consider artificial feeding a potential health threat to the fed animals due to the belief that prolonged congregation of animals around a feeding site increases the probability of disease transmission. This increased probability is generally irrespective of how the disease is transmitted, i.e., direct contact, aerosol, environmental contamination, or infected feces and urine.
Positive benefits of feeding include: increased winter survival, increased disease resistance (an increased plane of nutrition enhances the immune system), and increased production (less offspring lost in utero as a result of malnutrition).
The elk feedgrounds in northwest Wyoming encompass benefits and detriments. Following are examples of current and potential diseases that impact, or could impact, elk maintained on winter feedgrounds.
Brucellosis is a highly contagious bacterial disease of both animals and humans recognized since the 19th century. Brucellosis is a disease of concern for wildlife, cattle, and humans. A cooperative state-federal brucellosis eradication program has existed for over 70 years to eradicate brucellosis because of its economic impact on cattle and because it can be a serious human disease. This generally successful program has nearly eliminated brucellosis in domestic livestock, but the disease still exists in free-ranging elk and bison in the Greater Yellowstone Area. Brucellosis is not known to exist in wildlife at any other locations in these states.
Brucellosis may have been introduced into the GYA from infected bison that were transplanted into Yellowstone National Park from a brucellosis-infected cattle ranch. In addition, elk may have contracted brucellosis when they fed on cattle feedlines in the early 1900s.
There are several Brucella species. Brucella abortus is the bacterium that infects elk, bison, and cattle. The current taxonomic scheme recognizes 8 biovars. B. abortus types 1 and 4 are probably the most common isolates from elk and bison in the GYA.
Infection of the female reproductive tract results in abortion. Cows usually abort their first calf following infection. A few cows will continue to abort their second, or even third, calf. Fetuses delivered near term often are stillborn or fail to thrive due to an overwhelming Brucella infection. The male reproductive tract (testes, seminal vesicles, prostate) can also be infected.
Infection of the bone or joint membranes results in lameness that may make the animal more susceptible to predation.
The most common route of transmission is thought to be oral as a result of an animal licking or ingesting infected fetuses, placentae, fetal fluids, or vaginal exudates. Under cool, moist conditions, Brucella bacteria can persist for more than 100 days in the environment and transmission may occur by animals grazing on contaminated pasture or consuming other feedstuffs contaminated by discharges or fetal membranes. Treatment of brucellosis in animals is generally unsatisfactory because it requires multiple drugs administered daily for several weeks.
WG&F vaccinates elk against brucellosis on 21 of its 22 feedgrounds. The Dell Creek feedground is maintained as an unvaccinated control with which to compare efficacy of vaccination on other feedgrounds.
WG&F tests elk for brucellosis at many of its feedgrounds. It also gathers blood samples from hunter-killed elk, which are thought not to winter regularly on feedgrounds. Seroprevalence data collected from 12 feedgrounds where elk have been vaccinated averaged 23.6 percent (range: 13-30 percent); the average seroprevalence of elk from the unvaccinated Dell Creek feedground has been 32 percent. The seroprevalence of elk not frequenting feedgrounds has averaged 2.3 percent. These data support the contention that feedgrounds increase the probability of disease transmission. Conversely, feedgrounds provide the only opportunity to effectively vaccinate elk and are one of the best methods to prevent co-mingling of elk and livestock during winter months.
Chronic Wasting Disease
Chronic wasting disease is a fatal disease of the central nervous system of mule deer, whitetailed deer, and Rocky Mountain elk. Chronic wasting disease has been found in primarily central and southeastern Wyoming. Chronic wasting disease is one of a group of diseases called transmissible spongiform encephalopathies that are thought to be caused by abnormal proteins or "prions." These prions are unlike viruses or bacteria in that they contain no DNA and, thus, are not living organisms. Deer hunt areas with CWD-affected animals experience progressive loss of body condition, reluctance to move unless approached closely, increased drinking, depression, and eventually death. Many animals are seen near water and are reluctant to leave such areas. All animals showing clinical signs of CWD eventually die; however, it is not known if just being infected with the prion always results in disease and death.
The mode of transmission of CWD has not been identified. Evidence suggests the disease can pass directly from infected animal to uninfected animal; by contact with soil, plants, or feed contaminated with the prion; or by direct or indirect contact with the carcass of an animal that has died from CWD. There currently is no evidence that CWD can be transmitted to humans or domestic livestock.
WG&F has conducted systematic surveillance for CWD since 1997 by examining hunter-killed deer and elk. Biologists remove lymph nodes from the head that are located just behind the curve of the jawbone. These lymph nodes are tested by an enzyme-linked immunosorbent assay (ELISA) test similar to one of the tests used for brucellosis. This test is highly accurate and can be conducted quickly. The overall CWD prevalence of deer found in the endemic area is 7.7 percent (range: 0.5-28.0 percent) whereas the prevalence for elk is 3.4 percent (range: 1.0-9.3 percent). It is unknown why more deer than elk are found to have the disease.
Also, a higher percent of buck deer test positive for CWD compared to does; it is unknown if more bull elk get CWD than do cow elk. In addition, 1,095 elk from the Jackson herd have been tested since 1997 and none were found to be infected.
The prevalence of CWD in captive elk or deer has been found to be much higher (59-85%) than for free-ranging animals. This is thought to be due to an increased opportunity for animal-to-animal transmission and/or exposure to an increasingly contaminated environment.
Mathematical models have been developed based on free-ranging and captive animal data. These models predict that over a period of several decades, CWD prevalence rates will increase with a concomitant decrease in population. Some assumptions of this model have been called into question by scientists and, thus far, there is no proven example of a wild population declining due to CWD.
Many people are concerned that elk on feedgrounds may mimic the circumstances of elk in captivity and suggest that feedgrounds will result in high CWD prevalence resulting in drastic population declines as implicated by the disease models. Although this may happen, a perfectly acceptable alternative hypothesis is that CWD will have little or no impact on elk populations based on the known low prevalence rates for CWD in wild elk. Although there are many opinions, no one knows what will happen if elk on feedgrounds become infected with CWD.
The only tool wildlife managers have employed to slow the spread of CWD is increasing the hunter harvest or otherwise culling deer in a CWD area. This increased killing does result in decreased prevalence simply because decreased numbers of deer result in decreased opportunities for disease transmission. Nonetheless, all attempts at culling have only resulted in lower deer numbers. As of August 2004, culling has not stopped the spread of the disease.
Many wildlife disease professionals believe that CWD cannot be stopped from spreading in the wild in the foreseeable future. If true, CWD will likely eventually infect elk in the GYA.
The only way humans have ever been able to control any disease is by developing a thorough understanding of the disease agent, the pathophysiology of the disease it causes, and its mode of transmission. Today, hundreds of research experiments are being conducted around the world to understand diseases like CWD. This research takes time, but eventually we will likely learn how to slow or stop the spread of CWD, how to protect animals from contracting CWD, or even how to cure animals already infected with the disease.
Tuberculosis (TB) is a worldwide disease affecting domestic and wild animals, birds, and humans. Tuberculosis is caused by bacteria of the genus Mycobacterium. Bovine TB, caused by Mycobacterium bovis, is of most concern to elk and bison in the GYA. Tuberculosis causes lesions in the lungs and elsewhere, resulting in emaciation and oftentimes death. Infections can be unapparent for years.
Bovine TB is not presently found anywhere near the GYA, but there have been cases of TB in game farms in Montana and Colorado. Currently, there are focal areas of bovine TB in freeranging white-tailed deer in Michigan and bison in Canada. Domestic cattle are capable of harboring TB and transmitting it to wildlife, but the disease has been nearly eradicated in cattle and is highly regulated to prevent its spread.
The disease is usually spread through inhalation of the bacteria by a susceptible host. High densities or artificial concentration of animals are thought to exacerbate the spread of TB. Although TB vaccines exist, none have been proven effective in preventing the disease in wildlife. Like brucellosis, individual animal treatment would be difficult in wild animals due to the need for long-term antibiotic treatment. Testing for TB in free-ranging animals is difficult because animals have to be held for three days to finish the testing process.
WG&F has sampled 2,532 elk in the GYA since 1992 and found no cases of TB. Today, TB surveillance is conducted in conjunction with CWD sampling because the lymph nodes examined provide evidence of either disease.
Prevention is the most rational management strategy for TB. This is being accomplished by continuous surveillance and examination of hunter-harvested wildlife. The nearly successful TB eradication program for cattle, and the recently implemented TB eradication program for farmed elk and deer, make it unlikely that TB will be introduced into wildlife of northwest Wyoming.
Reduction or elimination of feedgrounds would not prevent the introduction of TB into the GYA, but feedgrounds could contribute to the maintenance and spread of TB should it arrive.
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