West Nile detected in Uintah mosquitoes

West Nile virus has been found in mosquitoes in Uintah County, according to TriCounty Health Department director Joseph B. Shaffer.

And a similar virus, this one responsible for Western equine encephalitis, was found in mosquitoes and a sentinel chicken in Washington County.

Both viruses can be passed to humans who are bitten by an infected mosquito, but there are no reports of human infection so far this year, according to Steve McDonald, spokesman for the Utah Department of Health.

"West Nile virus is really difficult to predict when and where it's going to show up," he said. "It really depends a lot on Mother Nature. But we're not going to be surprised to see it show up again in other parts of the state."

Four of Utah's six neighbors had already detected West Nile virus this year. Nationally, more than half of states report the virus and so far there have been 41 cases in humans and one death.

Both types of virus were detected by the surveillance system that was activated in May. Statewide, mosquito pools are checked, as are sentinel chicken flocks. Surveillance efforts run until the first hard freeze, which is when the mosquito population dies down.

The encephalitis was found in areas where people go for recreation, said Phil Hofeling, speaking for the Southwest Utah Public Health Department. Shaffer said the West Nile was found in the Ouray Wildlife Refuge, "not really a big recreation area."

The viruses are similar in several key ways. Both are carried by the Culex tarsalis mosquito, which flies between dusk and dawn. Infection can spread to birds, horses and humans. And in both, the severity of infection ranges from hardly noticeable to lethal.

Less commonly, the virus responsible for equine encephalitis can invade the central nervous system and cause severe complications and death. Like West Nile, it has no specific treatment. With both viruses, efforts focus on prevention, by controlling mosquitoes and wearing repellents containing DEET. Mild symptoms of the encephalitis include a severe headache and fever, while those with severe disease may have a sudden high fever, headache, drowsiness, irritability, nausea and vomiting, followed by confusion, weakness and coma. Young infants may go into a seizure. The symptoms appear about 5 to 10 days after the bite from an infected mosquito. About 13 percent of those bitten experience the major complications, and 3 percent of them may die.

Vaccine is available for horses, but not humans.