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USDA researchers attack the disease from three different angles. The United States Department of Agriculture (USDA) researchers have been trying to unravel how diseases are spread from animal to animal through ticks, flies, midges or other insects, also known as vector-borne diseases, according to the Agricultural Research Magazine, published by the USDA. The virus bluetongue is one of the most important of these vector-borne diseases to United States livestock producers. Bluetongue has a significant impact on cattle producers-even though infected cattle do not become noticeably ill. This disease has the ability to spread across international boundaries. As a result, countries without bluetongue restrict the importation of animal products from countries that have the disease. This costs U.S. livestock producers $125 million annually in lost trade and testing to certify the animals do not carry the disease. The USDA also does this to keep other strains of bluetongue out of the country. How Science is Involved Scientists at the Agricultural Research Service's Arthropod-Borne Animal Diseases Research Laboratory in Laramie, Wyo. are studying the three components of the bluetongue problem: insects, animals, and the virus. Researchers are trying to find out how bluetongue spreads and whether it can be spread from cattle after a finite period of time. This information could impact trade by easing restrictions in some areas of the country. Parts of the United States could be declared free of bluetongue because the biting midges in the Northeast do not spread the virus. Removing Barriers Research has found that vectors for the disease are dormant during the winter in cold areas. This has resulted in Canada allowing trade from northern states during these cold months. Scientists have found both ecological and genetic support for declaring several northern states free of bluetongue. Number of Species Over 110 species of Culicoides midge, also known as biting gnats are found in the United States. Researchers thought a complex of three sub-species, C. variipennis variipennis, C. variipennis sonorensis and C. variipennis occidentalis were involved in the spread of the disease. USDA researchers have actually identified these as three separate species. "Several researchers here have shown over the past few years that variipennis doesn't have the ability to spread bluetongue. And we've shown that sonorensis is the primary vector," says Walter J. Tabachnick, ARS entomologist in Laramie, Wyo. "If we can prove this genetically, regions with only variipennis should be safe from bluetongue." Sonorensis and occidentalis are found in parts of the South and in western states, while variipennis lives in the Northeast. "In virtually every case where bluetongue has been detected in cattle in the Northeast, the animal came from another part of the country," he says. Edward T. Schmidtmann, also an ARS entomologist, has found environmental factors that support the existence of three species in the C. variipennis complex. Larvae of all three live in aquatic sediments, but "levels of salt and boron correlate with which species is present," he says. "Although we don't have specific practical management suggestions, this work indicates that sonorensis populations could be controlled through environmental management," Schmidtmann says. Tests for Bluetongue and EHD ARS microbiologists are also looking at the virus's proteins and genes which has led to improved diagnostic procedures for bluetongue viruses and related viruses that cause epizootic hemorrhagic disease, or EHD. "EHD causes an often fatal illness in white-tailed deer, and it can give cattle a bluetongue-like disease," says James O. Mecham, ARS microbiologist. "For trade purposes, it is very important to be able to tell the two diseases apart." The midges that transmit bluetongue can also spread EHD. "Understanding factors that govern the role of the insect vector in the disease process, the genetics and evolution of the pathogens, and the effects on the animal host will be the basis for reducing the impact of these pathogens on animal health in the next millennium," says Tabachnick |
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