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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

DNR Wildlife Health Assistant Barb Walser (tan coat with back to camera) ages a deer before extracting tissue from the base of the skull. Tissue samples are used to test for a number of diseases. © Robert Queen
DNR Wildlife Health Assistant Barb Walser (tan coat with back to camera) ages a deer before extracting tissue from the base of the skull. The tissue sample is used to test for a number of diseases.

© Robert Queen

October 2001

Keeping an eye on the border and the future

Early detection of emerging wildlife diseases protects the health of deer, livestock – and humans.

Shawn Marchand


The Big Three | Safety steps for hunters
Field checking the herd | Watch out for foot and mouth
Future vigilance

It's his watchful eye as much as his skillful work with a knife that put Tom Bechle on the front line in Wisconsin's battle to fend off wildlife disease. Last October, Bechle was cutting up a deer at the Brost Meat Market in Kiel when he noticed black spots inside the buck's chest cavity. The spots reminded Bechle of those depicted in a brochure for hunters on bovine tuberculosis (TB). He immediately stopped butchering the animal and telephoned Jeff Colon, a meat inspector from the Department of Agriculture.

A state inspector came quickly, took samples from the deer, and sent the tissue to a lab for analysis. Fortunately, the animal tested negative for TB, and Wisconsin still has a clean record – bovine TB never has been detected in our wild deer. However, since 1997, four cases have been reported in captive elk herds in Manitowoc County.

Bovine TB is just one of the "emerging" diseases tracked by wildlife, agricultural and public health officials in Wisconsin. These new ailments or existing diseases "are occurring more frequently, spreading over a wider geographic range, or developing resistance to known treatments," according to Julie Langenberg, Wisconsin DNR wildlife veterinarian.

Identifying and controlling disease in Wisconsin's wildlife protects hunters and others who eat game, sustains healthy wildlife, provides safe outdoor recreation and supports wildlife-related industries.

Monitoring disease in Wisconsin's wildlife also helps safeguard the health of livestock. Free-ranging deer and livestock can transmit bovine TB to each other. In Michigan, disease researchers believe wild deer were infected with TB several decades ago through contact with sick cattle. Now, TB in wild deer populations has infected several cattle herds and cost Michigan's livestock industry millions of dollars.

Wisconsin's nearly 160 custom meat processors also have a stake in protecting themselves, their businesses and their customers from wildlife diseases. In factories and commercial meat markets where domestic animals are slaughtered and processed, at least one meat inspector from the Wisconsin Food Safety Division is on hand to inspect carcasses and monitor equipment sanitation. But small custom butcher shops that only process deer for customers without retail sales to the public are not inspected, and it's up to the owner to recognize any diseased animals.

"The vast majority of deer are prepared at state-inspected plants," notes Terry Burkhardt, director of Wisconsin's Meat Inspection Program. Small custom processors may not butcher large numbers of deer, but it's still vital to alert them to the signs of disease.

The Big Three

Three emerging diseases to watch for are bovine tuberculosis (TB), cranial abscessation syndrome (CAS) and chronic wasting disease (CWD).

Bovine tuberculosis (TB) develops when the bacterium Mycobacterium bovis attacks the respiratory system of goats, dairy and beef cattle, elk, deer and other ruminants. Only 45 percent of deer that carry TB show signs like tan or yellow lumps on the inside surface of the rib cage or lung tissue. Most deer with TB show no signs all or simply look emaciated. Consequently, it's difficult for hunters to recognize TB when hunting or field dressing deer.

Though scavengers or carnivores can contract TB by eating diseased carcasses, transmission from handling or consuming infected meat is very rare for both animals and people. TB more frequently spreads as sick animals sneeze or cough bacteria-laden air on other animals or food, according to Steve Schmitt, veterinarian for Michigan's Department of Natural Resources.

The telltale white-yellow nodules on the rib cage of a deer infected with BT. © Michigan DNR
The telltale white-yellow nodules on the rib cage of a deer infected with BT.

© Michigan DNR

"There is no evidence of any hunters in Michigan getting bovine TB from deer," says Schmitt. Bovine TB was first diagnosed in the northeastern Michigan deer herd in 1994. Since then, TB has been confirmed in 285 deer, a dozen carnivores that feed on deer, six cattle herds, a captive deer herd and a goat herd.

Containing the disease is expensive. The Michigan Department of Natural Resources has spent $2 million dollars in prevention and surveillance. Michigan DNR and the livestock industry have spent $97 million attempting to contain and eradicate the disease, and the state is building a new $58 million diagnostic lab.

Cranial abscessation syndrome (CAS): Bill Ishmael, DNR wildlife biologist in Spring Green, responded promptly when he received reports that a deer in northwestern Sauk County was walking in circles, acting disoriented and lacking any fear of people. When Ishmael arrived on the scene, the deer was standing with its head down and did not react to him. As he got closer, Ishmael noticed the buck's antlers had broken off; pus was exuding from the base of the antlers and the animal's eye sockets. "It seemed as if it were blind," Ishmael noted.

All of these symptoms are characteristic of CAS, a disorder regularly found in Wisconsin's wild deer. The bacterium that causes CAS, Arcanobacterium pyogenes, is found naturally in the mouths of healthy Wisconsin deer, but can cause infections through broken antlers, abrasions in antler velvet, or through any open wound on a deer's head. After entering through the skin, the bacterium can "eat" through the deer's skull, causing abscesses in the brain.

CAS occurs most commonly between October and April and may account for up to six percent of the natural mortality in bucks. "This disease affects adult antlered deer almost exclusively," says Kerry Beheler, DNR wildlife health specialist. The annual cycle of shedding antlers, getting nicks when new antlers are in velvet, and rutting battles provide plenty of opportunity for head wounds through which CAS bacteria can enter.

A nick or wound in the antler vellum provides an entrance for he bacterium that causes cranial abscessation syndrome in deer. © DNR Wildlife Health Unit
A nick or wound in the antler vellum provides an entrance for the bacterium that causes cranial abscessation syndrome in deer.

© DNR Wildlife Health Unit

"We know that CAS can cause loose or deformed antlers, or kill trophy bucks," Beheler said, "but we don't have enough data to gauge the impact on the whole buck population."

In theory, meat from a deer infected with CAS isn't unhealthy and can be eaten if cooked thoroughly until the juices run clear. In practice, it's not advisable to eat such meat because the bacterial infection can make the meat tough and unpalatable.

Chronic wasting disease (CWD) is a fatal degenerative brain disease of elk, white-tailed deer, and mule deer. It has never been found in Wisconsin and appears to pose little health threat to people or livestock, but it's closely related to diseases that are killers. CWD is a form of transmissible spongiform encephalopathy (TSE), a disorder that causes sponge-like holes to form in and around brain cells. Other TSE's include scrapie in sheep, bovine spongiform encephalopathy (BSE) in cows (mad cow disease) and Creutzfeldt-Jakob Disease (CJD) in humans.

CWD was first found in a captive mule deer at a Colorado research facility in 1981. Since that time, CWD has been diagnosed in wild elk and deer populations in Colorado, Wyoming, Nebraska, and Saskatchewan, and in captive elk in South Dakota, Colorado, Montana, Oklahoma, Nebraska and Saskatchewan. The disease is spreading very slowly among wild deer in northeastern Colorado, southeastern Wyoming and extreme western Nebraska.

An elk suffering from CWD - emaciated, disoriented and drooling uncontrollably. © Dr. Beth Williams, DVM, Wyoming Dept. of Veterinary Services
An elk suffering from CWD – emaciated, disoriented and drooling uncontrollably.

© Dr. Beth Williams, DVM, Wyoming Dept. of Veterinary Services

Symptoms of CWD include progressive weight loss and behavioral changes such as a lack of awareness, lowered head, drooping ears, excitability, repetitive walking, teeth grinding, excessive salivation, difficulty swallowing and a rough, patchy coat. Symptoms may not be visible for months or years after infection.

Many researchers now believe that CWD and the other TSE's are caused by microscopic, infectious proteins called prions (PREE-ons) that can change normal healthy proteins. The World Health Organization has said there is no scientific evidence that CWD can infect humans, but test tube studies have shown that CWD prions can slowly alter healthy human prions.

Prions are difficult to eradicate. According to Barbara Walser, DNR wildlife health technician, heat, ultraviolet light, radiation or common disinfectants cannot break down prions. They are undetectable by the immune system, and there are no tests to detect and diagnose CWD in live animals.

Although the exact mechanisms by which CWD spreads are unclear, those studying the disease believe animals infect each other through contact with bodily fluids. There is also worrisome evidence that CWD prions may persist in the environment and infect deer that have never had direct contact with a diseased animal.

Wildlife health officials are concerned that deer and elk infected with CWD could be imported into Wisconsin from areas where the disease persists at low levels. On three occasions, elk have been quarantined on Wisconsin game farms because they were imported from a CWD-infected farm in another state. Farmed deer and elk are fenced in, but escapes or entry by wild deer that hop fences could allow contact between captive animals and wild deer.

Wisconsin game farms holding captive elk or deer are encouraged to participate in a voluntary testing program to screen for signs of the disease. All dead animals over 18 months of age are tested, regardless of the cause of death. A clean bill of health is vital to those farms that want to sell elk to other states. Montana, for example, requires an out-of-state game farm to be CWD-free for five years before animals from that farm can be imported. Currently, Wisconsin does not require similar certification before animals can be brought into the state.

Safety steps for hunters

Wisconsinites who hunt big game in western states should take additional precautions to protect themselves and their home turf. Those hunting deer and elk where CWD infections occur should avoid shooting an animal exhibiting any CWD symptoms unless the hunters are willing to tag and donate these animals for testing. Wear disposable gloves when field dressing your harvest and dispose of offal properly so other animals won't be exposed to it. don't even consider eating internal organs like the brain or spleen or the spinal cord.

If deer are harvested from areas where TB or CWD have been detected, don't make the meat into sausage or jerky, because the cooking temperatures used in these preparations are not high enough to kill many bacteria. Have your harvested game completely processed and packaged out West to lessen the chance of carrying infection back to Wisconsin. Local deer might feed around the discarded remains of deer or elk that were partially dressed after returning to Wisconsin, notes Langenberg. Bringing back fully processed animals definitely lowers the risk of spreading disease.

Field checking the herd

Since 1996, the DNR Wildlife Health Team has analyzed samples from a sick deer, from deer removed by sharpshooters and from deer harvested by hunters to get early warnings of wildlife diseases. Each year the team selects at least six deer registration stations closest to sites where disease outbreaks might occur – near elk or deer farms that have experienced significant disease outbreaks, near spots where animals were quarantined, and near areas with high densities of wild deer and deer farms.

No edible meat is sacrificed in the testing. If hunters choose to participate, two lymph nodes from either side of the deer's jaw are collected and tested for TB, and a small portion of the animal's brainstem at the base of the skull is taken to check for the presence of CWD.

"Our hunters really care about having healthy deer in the state," says Langenberg. "They are highly receptive to the testing and we really appreciate that cooperation."

This year, the disease trackers hope to test at least 500 animals. "It would be great to double that number," Langenberg said. "We need to test a lot of animals to stand a chance of detecting rare diseases that occur at low levels."

Aside from taking part in disease testing at registration stations, Wisconsinites can help keep deer populations healthy by reporting sick or abnormal-looking deer to a local DNR office or the DNR Wildlife Health Program at (608) 267-6751 or (608) 266-3143.

"There's another step we can take, and I know it's not popular," Langenberg says, "but curtailing deer feeding and baiting would help.

"Scientists in Michigan demonstrated a connection between the spread of TB and activities like feeding and baiting that promote deer to gather in close proximity. Limiting these practices would help prevent a significant disease outbreak."

Watch out for foot and mouth

Foot and mouth disease (FMD) is a highly infectious ailment of cloven-hoofed animals including cattle, sheep, swine, bison, deer and elk. This disorder causes the hooves and mouth to blister, making it difficult for the animal to chew and forage for food.

Caused by an airborne virus that persists for a long time in the environment, FMD can be carried to different locations on clothing and equipment.

Containing an FMD outbreak in Great Britain has been very expensive and has changed people's habits in a hurry. Beef sales plummeted and the country spent the equivalent of $28 billion this year quarantining areas, sacrificing herds and containing outbreaks. FMD also has been detected in Africa, South America and Asia.

FMD has not been found in the United States since 1929, but if it were reintroduced, it could spread rapidly in livestock and wildlife populations. The United States Department of Agriculture and the State Department of Agriculture, Trade, and Consumer Protection have created task forces to anticipate how to deal with FMD in livestock. Controlling the disease in wildlife, however, is "all a big unknown," according to DNR's Langenberg.

Future vigilance

Given Wisconsin's large, healthy deer herd and known disease outbreaks elsewhere, our need to monitor emerging wildlife diseases will only increase. Finding and containing these diseases is no simple task, especially when wild deer populations remain large and widespread, the captive elk and deer farming industry is growing, and both wild and domestic animals are frequently transported to and through Wisconsin.

Vigilance is the key, through continued monitoring, emergency planning with animal regulators, cooperation from animal industries and help from hunters.

"We need as many eyes in as many places as possible to provide early warning of diseases that can be terribly costly if they get away from us," Langenberg says.

Shawn Marchand writes about wildlife and forestry issues for DNR's Communication and Education program in Madison.