C6—Lancaster Farming, Saturday, Dtcwbf 3,19*3 DENVER, Colo. Because gnats bite farm animals, million* of dollars in potential U.S. exports of livestock and semen for ar tificial insemination are lost each year. Scientists at the U.S. Depart ment of Agriculture say the losses occur when the gnats bite sheep and cattle, transmitting a viral disease called bluetongue. Technically, the gnats are biting midges named Culicoides variipennis. These bites, multiplied into the millions, cost the livestock in dustry an estimated $3O million yearly in exports, say the scien tists. According to research veterinarian Dr. Thomas E. Walton of USDA’s Agricultural Research Service in Denver, Colo., identifying infected animals is not easy and that makes it hard to cut the losses. The research agency is doing the research in cooperation with USDA’s Animal and Plant Health Inspection Service and Foreign Agricultural Service. Elusive disease Walton characterizes bluetongue as “an elusive and complicated disease” that strikes sheep, cattle, goats, and even such wildlife as deer. What makes the disease elusive, Walton says, is that an infected cow or sheep, for example, may show no clinical signs at all. s Infected sheep may have a blue, swollen tongue, as well as swollen ears and lips, says Walton, but not always. Moat adult victims recover, although pregnant ewes may die. Walton says bluetongue becomes obvious, and a deadly serious disease, when affected animal* lose their offspring through spontaneous abortions, stillbirths and birth defects. Some of the Members of the German Rural Youth Organization toured Atlantic Breeders Cooperative Wednesday as part of a 14 day exchange tour to the United States. American FFA youths and their families are hosting 18 German exchange students. While in Pennsylvania the group is being hosted by students in the Garden Spot, Ephrata, and Twin Valley FFA chapters. Pictured are, from the left, Irmtraud Tiemann, Reinhold Meisterjahn, Baerbel Reibold, Bernd Maier, Hansjoerg Rueede and Gerhard Henn. The group also toured the Sperry New Holland Museum and Victor Weaver plant. Before retunring to West Germany they will sight see in Washington, D.C. and New York City. Researchers seek better control of gnats offspring that do survive may look healthy but may be long-term carriers of the disease. Walton, who heads the research agency’s Arthropod-borne Diseases Research Laboratory, is one of a team of scientists sear ching for keys to the disease. Currently, the team is focusing its research on identifying and understanding the bluetongue virus itself. “What complicates the research,” Walton says, “is the fact that, worldwide, the virus exists in 23 known strains, called serotypes. “That’s equivalent to saying bluetongue is 23 separate diseases in terms of the animal’s susceptibility.” Similar situations exist in humans. One polio vaccine protects people against only one of the three polio types. For full vaccination, people must be vaccinated three times. Until this year, only four bluetongue virus strains were found in the United States. Just this spring, a fifth serotype was isolated from blood samples from Florida by veterinarian Dr. T. Lynwood Barber and microbiologist Dr. Ellen Collisson of the Denver laboratory. The blood samples were collected by Dr. E.P.J. Gibbs, a veterinarian at the University of Florida. Laboratory researchers there and other experts had thought that only one primary carrier, the Culicoides variipennis midge, transmitted the disease in this country. As a result of the isolation of the new serotype, Barber has confirmed the existence of a second midge carrier. Culicoides insignia. “They are not just flying syringe Lancaster FFA hosts German exchange students 23 strains Second carrier f* "Waltons iney tgnats) become infected too,” he adds. “But apparently they are not hurt by the presence of the virus, even though it reproduces within the gnats’ bodies, sometimes in surprisingly large quantities.” One mysterious feature of the bluetongue disease is call “showering,” says Walton. With showering, an animal may be harboring viruses in an inactive stage within its body, so scientists may not be able to isolate the virus from the animal’s bloodstream. A special stimulant, or stress, can reactivate the virus to enter the animal’s bloodstream. Saliva from a midge bite is such a stimulant. Virus showers When a gnat bites a carrier, the virus showers into the Mood stream. The next gnat to bite the host subsequently contracts the infection and passes it along. Viruses that go dormant and then become reactivated are common. An example in humans is the Herpes virus that causes cold sores. Bluetongue isn’t always passed by gnats, however. “The disease also can be passed to the offspring from either in fected parent,” says Walton, in a process called vertical tran- t A smission. Uninfected cows can contract bluetongue through natural or artificial insemination; the latter is a routine practice of the cattle industry. Walton figures that, for the in dustry, bluetongue is the second most common restriction to free international movement of livestock after foot-and-mouth disease. " gnats USDA analyses indicate the U.S. loses |lO to $l5 million yearly in exports of both cattle and semen to New Zealand and Australia because of bluetongue and another $lO and $l5 million in exports of cattle to the United Kingdom. In other cases, producers must test and certify animals for export to be free of bluetongue, at a cost of about $l,OOO for a 100-head herd. Members of the European Economic Community have vir tually closed their markets to U.S. cattle and sheep, a problem that might be solved by finding a way to control bluetongue. Researchers for USDA, land grant universities, industry and foreign countries are working to create a vaccine that will enable livestock producers to protect herds against the disease. 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Temperature seems to limit how far the gnats can carry the bluetongue virus. Culicoides carriers are known to range from the Arctic Circle into Mexico and Florida, but the gnats do not transmit the disease in New England or in states bordering the Great Lakes. Currently, Walton says, the best control is an integrated pest management approach that combines pesticide application and water management of breeding sites where female Culicoides lay their eggs.
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