Aleutian disease is ravaging Utah's $100 million mink industry. Mortality in infected herds approaches 25 percent. Some producers have liquidated herds. Others are on the verge of going out of business.
"Aleutian disease is probably the most serious livestock disease in the state at the moment. If this disease afflicted any other species of farm animal it would receive a lot more attention," says Le-Grande Ellis, a Utah State University physiologist who has studied reproduction and pelt production in mink for 20 years.In a recent issue of Utah Science, published by the Utah Agricultural Experiment Station, Ellis explains the virus responsible for Aleutian disease triggers excessive production of antibodies, and blood becomes noticeably thicker. Eventually, so much antigen and antibody are deposited in the kidneys and liver that these organs are attacked by the animal's immune system.
The disease appeared more than 50 years ago, and hasn't been much of a problem since tests have allowed ranchers to identify the problem. Ironically, those tests may be partially responsible for the severity of recent outbreaks, Ellis says. Some of the infected mink that were culled may have had some natural resistance to the disease.
"When the disease hits now, it wipes out whole herds because none of the remaining mink have been exposed to the virus," he says.
Researchers with the Utah Agricultural Experiment Station are attacking the problem on several fronts. The research team consists of Ellis, and virologists John Morrey, Dale Barnard, and Keven Jackson.
There is little evidence that a more virulent strain of the disease has appeared, but that is one possibility researchers will examine.
The virologists are studying an agent that may enhance the immune system's ability to ward off the virus; the compound may also have antiviral properties.
"In preliminary experiments, this compound seemed to reduce the severity of the disease," Barnard says. "We are conducting clinical trials to determine the optimum dose, timing, and formulation of the compound."
Jackson, who is also a veterinary pathologist, is developing a vaccine against the disease. The researchers will also identify the genes responsible for resistance to the disease. Such transgenic animals may provide a long-term solution to the problem. Ellis is also determining whether it is possible to select and breed mink with natural resistance to Aleutian disease.
Researcher are cooperating with Gary Durrant at the Utah Fur Breeders Agricultural Cooperative in Sandy to determine how the virus is transmitted. Many ranchers believe skunks and raccoons harbor the virus and there are several accounts of outbreaks following exposure to raccoons.
Feral mink are certainly prime candidates for spreading the virus. "I certainly wouldn't start shooting wildlife indiscriminately. I would recommend eliminating feral mink from ranches. Ranchers may underestimate the number of feral mink and the ability of feral mink to transmit the disease," Barnard says.
In Utah, mink production is concentrated in a few areas and ranches are often close to each other, which aids the spread of the disease.
Some strains (color phases) of mink are resistant to the virus. Unfortunately though, mink with desirable pelt colors Aleutian, dark, and pastel color phases are susceptible.
Inbreeding for coat color increase susceptibility to the virus, even though the traits may not be linked. Ellis notes that the genes controlling coat color, reproduction, and immunity are on the same chromosome. "Once a `bad' gene is found on the chromosome, it's very difficult to eliminate," Ellis says.
Utah often leads the nation in pelt production. Aleutian pelts command nearly twice the price of standard pelts. Ranchers who switch to resistant strains of mink with less desirable coat colors probably couldn't afford to stay in business.
Aleutian disease plagues mink ranchers in Russia, the People's Republic of China, Holland, Scandinavia, Canada, Iceland and areas throughout the United States. Recent unfavorable publicity concerning the production of fur-bearing animals may have diminished support for research to combat the disease, Barnard says.