UC-Davis develops vaccines for Rift Valley fever

Davis, Calif. — Veterinarians at the University of California-Davis (UC-Davis) say they have developed two genetically engineered vaccinates to combat Rift Valley fever, a mosquito-borne disease that affects livestock in Africa and the Middle East.

Researchers from UC-Davis, working with scientists at the University of Connecticut and the University of Texas Medical Branch, published their findings in the online edition of Proceedings of the National Academy of Sciences.

"There currently are no approved vaccines available for treating Rift Valley fever in humans, and those available for livestock are either inefficient or have serious side effects," says lead author Tilahun Yilma, a veterinary professor specializing in viral diseases and the director of the International Laboratory of Molecular Biology for Tropical Diseases in the UC-Davis School of Veterinary Medicine. "Because Rift Valley fever is spread by mosquitoes, there is concern that the disease could be accidentally or intentionally introduced to North America and other regions where it is not now found. Such an introduction could have devastating economic and human health implications."

Rift Valley fever is a viral disease first identified in 1931 among sheep in the Rift Valley of Kenya, according to UC-Davis. Since then, outbreaks have been reported in Sub-Saharan and North Africa, with a major outbreak of the disease in 1998 in Kenya, Somalia and Tanzania.In 2000, cases of Rift Valley fever were reported in Saudi Arabia and Yemen, the first reports of the disease outside of the African continent. UC-Davis says this raised concern among health officials that the disease might spread to Asia, Europe and the Americas.

The disease can cause major livestock losses, with the rate of abortion among pregnant sheep approaching 100 percent. In people, infection can cause fever, hepatitis, vision loss and hemorrhagic fever.

In developing the vaccines, researchers used the vaccinia virus, the same virus used to make the smallpox vaccine. They inactivated two vaccinia genes to weaken that virus and prevent it from causing disease, and inserted two Rift Valley fever genes to stimulate an immune response, thereby equipping the vaccinated animals to fight off infection, says UC-Davis.

One of the vaccines includes an additional gene to further weaken the vaccinia virus and enhance the safety of the vaccine. The vaccines proved 90 percent effective in trials with mice. The researchers say both vaccines would be easy to produce on a large scale and wouldn't require refrigeration.

Additional tests are planned on sheep and cattle, according to UC-Davis.