As if West Nile virus (news - web sites) wasn’t bad enough, now U.S. health officials are on the lookout for another mosquito-borne disease, fearing it could become a permanent part of the American landscape if it entered the country. Rift Valley fever, which originated in Africa, is the only disease at the top of both human health and agriculture lists of dangerous diseases. The virus can kill people, with a near 1 percent mortality rate, making it deadlier than West Nile. But Rift Valley poses a greater threat to cattle and sheep. It kills up to 30 percent of the livestock it infects and if it were found in animals here, it would probably prompt livestock bans by other countries.
