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WAFWA

Mule Deer Diseases

You can walk into any center for human disease control in the United States and get as much information as you want on both common and uncommon diseases in people. Wildlife biologists wish the same could be said for wildlife diseases.

While humans have places such as the National Center for Infectious Diseases and the Center for Disease Control and Prevention, biologists aren't as fortunate. Organizations such as The American Association of Wildlife Veterinarians, the National Wildlife Health Center and Wildlife Diseases Association exist to help monitor wildlife diseases. But the weak link in the chain is getting reliable, consistent, quality data to these organizations.

Biologists usually have to rely on large-scale die-offs or individual case studies to track and monitor wildlife diseases. The behavior of wildlife, low numbers of animals observed, lack of training and cost to monitor individuals within a population make studying wildlife diseases even more difficult.

Biologists face other hurdles. Large numbers of observations are required to detect and monitor diseases in wildlife populations. And many of the biologists capturing the wildlife are not trained to collect and handle scientific samples for analysis in a laboratory. Lack of adequate staff and lack of training make it difficult to monitor wildlife diseases.

Cost is another critical factor that prevents biologists from tracking wildlife diseases. Monitoring animals requires capturing, tagging and following those individuals. For longer-lived animals or animals with larger home ranges, these costs are prohibitive for many fish and wildlife organizations.

Difficulties aside, what do we know about disease in mule deer? First, while there are several diseases that affect individual mule deer, only two are known to wreak enough havoc to cause significant die-offs.

The diseases are viral and they cause blood loss. As a result, they are called hemorrhagic (hem-or-agic) diseases - bluetongue (BTV) and epizootic hemorrhagic disease (EHD). Diagnosis of these diseases is difficult because it's tough to tell one disease from the other.

Two other diseases, chronic wasting disease and tuberculosis, are considered emerging diseases.

Hemorrhagic (Bleeding) Diseases

Bleeding diseases were first identified in white-tailed deer populations, where death rates as high as 50 percent were documented. Mule deer fare better with these diseases, usually suffering no more than a 20 percent mortality rate. The diseases are common only in late summer and fall until the first freeze kills the transmitters of the virus, biting midges. Those deer that die usually do so within five to 10 days after being bitten by an infected midge.

When mule deer contract either of the two hemorrhagic diseases, they can show one or more signs of sickness. These include bleeding from the eyes, ears, mouth and/or nostrils, moderate fever, depression, anorexia, excessive drooling, swelling and ulcers in the cheek or tongue (thus the name blue tongue), swelling of one or more of the linings in the stomachs and blood in the feces and saliva.

Chronic Wasting Disease (CWD)

Chronic Wasting Disease (CWD) is so named because it causes chronic weight loss that eventually results in death. It was first documented in captive deer in a wildlife research center in Colorado in 1967.

Since then, it has been diagnosed in captive and free-ranging deer and elk in northeastern Colorado, southeastern Wyoming, Nebraska, South Dakota, Wisconsin and New Mexico and in game-farmed cervids in Colorado, Montana, Nebraska, Oklahoma, South Dakota and Alberta and Saskatchewan, Canada.

Loss of fear of humans, weakness, inability to stand, dehydration, listlessness, repetitive walking in set patterns, dull coat, excessive drooling, drooping head and ears, inability to control muscle movements and emaciation are signs of CWD.

CWD is a transmissible spongiform encephalopathy (TSE), which refers to the fact that in late stages of this disease, the brain becomes full of holes like a sponge. The disease usually takes years to develop, but it can develop in a relatively short period of time.

Scrapie is the oldest of the TSE diseases, and occurs in sheep and goats. It was first reported in the mid-18th century, but has never been reported in other animals or people. Affected animals lose control of their leg and body muscles that causes them to stagger. Eventually they cannot stand. The name "scrapie" refers to the fact that the animals can become irritable and develop an intense itch that leads the animal to scrape off their wool and break the skin.

Dr. Elizabeth Williams is a professor of Veterinary Science at the University of Wyoming and an expert in the field of wildlife diseases. She said chronic wasting disease is high on the list of priority wildlife diseases to monitor.

"Because of the concern about similar diseases such as scrapie in sheep, CWD is among those diseases the United States Department of Agriculture is interested in eradicating. It will be important in the future," said Williams.

Scientists have not determined what causes chronic wasting disease, but the most accepted theory is that cell proteins called prions (pronounced preeons), change and become disease-causing agents. Many believe the disease is transmitted from animal to animal, like scrapie.

"CWD and the other diseases are similar, but not identical," said Williams. "A lot of the features in scrapie are similar to deer. Clinically, deer don't scratch and itch, but many of the other symptoms are alike."

Increased monitoring by wildlife agencies, increased media attention, stronger public interest in the disease as a result of mad cow disease, and increased numbers of people moving into areas that were once wildlife strongholds likely have resulted in higher detection rates.

Tuberculosis

Another disease of importance to wildlife managers and veterinarians is tuberculosis. Tuberculosis is caused by bacteria, and is spread by direct and indirect contact between animals. Tuberculosis usually affects the lungs, causing difficulty breathing, coughing, and discharge from the mouth or nose.

The United States Animal Health Association (USAHA) is a sciencebased national forum interested in the eradication of tuberculosis from wild and domestic animals in the United States. It appointed a working group in October of 2000 to develop strategies to address tuberculosis issues.

The first diagnosis of tuberculosis in white-tailed deer occurred in the State of Michigan in 1974. Feeder cattle, dairy cattle and captive cervids, along with wild white-tailed deer and many carnivorous species have been infected. Williams said tuberculosis has not been found in any deer populations in the West, but that it is a disease of concern because of its ability to spread rapidly.

"Right now, we don't have any evidence of TB in free ranging populations in the West, but we know it's transmitted readily when deer are concentrated," said Williams. She said it is a disease that needs to be closely monitored because of its potential impact to wildlife and humans.

Jim deVos, Chief of Research with Arizona Game and Fish Department, places a strong emphasis on the importance of increased wildlife research to monitor wildlife diseases.

"I believe it is important that entities with management authority for mule deer make a more serious commitment to disease research," said deVos. "Only when large-scale die-offs occur do diseases become an important issue for wildlife management agencies. By then, it is often too late to do anything other than document the number of mortalities."

DeVos recommends a more aggressive, coordinated approach to wildlife disease research. This includes increased communication between the western states, coordination of veterinarians in western states working on wildlife research projects, creation of a consistent funding base to study mule deer health issues, development of standard sampling protocols so that all mule deer captured for any wildlife research purposes are sampled consistently and using quality standards, and participation in surveillance programs for diseases with high biological or social concerns for mule deer or human health.

If western states and Canadian provinces take this approach to wildlife disease research, there may someday be a place people can go to learn everything they ever wanted to know about wildlife diseases.