Research findings developed during 30 years of studies by the UC Davis School of Veterinary Medicine and an international research consortium suggest that parts of the United States can eventually be declared free of "bluetongue," a viral disease that has had significant economic impact on the livestock industry.

The research produced an increased understanding of the ecology of infection, which indicates that animals can safely be moved from areas in which the bluetongue virus infection occurs.

Bluetongue virus, which primarily affects sheep and wild ruminants like deer, poses no danger to human health but does result in costly trade interruptions. For example, even though the disease rarely occurs in cattle, the U.S. Department of Agriculture estimates that bluetongue costs U.S. cattle producers about $125 million annually in unnecessary trade restrictions, plus the expense of health-monitoring programs.

Research conducted by UC Davis veterinary scientists and their international colleagues has revealed that the disease is only spread by a certain species of biting fly called a midge, that cattle may carry the virus but rarely show symptoms, that infections in cattle are transient not persistent, and that climate and weather patterns affecting the midge are the best predictor of how the virus will spread. The researchers also have developed new diagnostic tests that can accurately detect all strains of the bluetongue virus and a new recombinant DNA vaccine that has none of the undesirable side effects associated with earlier vaccines.

"It is increasingly evident that bluetongue virus has not recently been spread globally through international trade of livestock or their semen," notes Bennie Osburn, dean of the UC Davis School of Veterinary Medicine. Osburn is widely known for his early research discoveries about bluetongue virus in sheep and cattle in the Western United States, and he has led two conferences of the international research consortium.

"Instead, research is confirming that bluetongue virus typically exists in distinct ecosystems in different regions of the world, and specific strains of the virus have likely co-evolved with different species of insects that transmit the infection," added James MacLachlan, a UC Davis professor and veterinary virologist, whose research team recently applied for a patent on a new recombinant bluetongue virus vaccine developed in collaboration with Merial Inc. and Sanofi Pasteur.

In May 2005, through efforts of the international research consortium, the 167 member countries of the World Organization for Animal Health (known by the French abbreviation OIE) revised the bluetongue section of the organization's Terrestrial Animal Health Code. Canada and other countries have eased their bluetongue import requirements during the past 10 years.

Osburn and MacLachlan note that global climate change poses the real threat because global warming expands the range of the insect carriers and facilitates the spread of bluetongue virus into regions in which it previously did not occur, including extensive portions of Europe.