More Utahns feeling West Nile's bite

Several dozen Utahns have now been diagnosed with West Nile virus. And cases are likely to continue for at least another few weeks, although active surveillance for the disease in northern parts of the state is winding down.

It takes several days with really cold temperatures to put Culex tarsalis, the mosquito that spreads the virus, into hibernation mode, says Lisa Wyman, a surveillance epidemiologist in the Utah Department of Health. Until then, people are at risk of being bitten and infected. And once the mosquitoes are gone, those who received their last bites still must wait a few days to see if they become ill. It takes from three to 15 days for symptoms to develop after infection.

Still, "today is probably the last day for the cooler areas to do sentinel chicken bleeds and check mosquito pools," she said Thursday. "The mosquito counts (in the traps) are down. We expect the warmer areas down south to continue for a while, maybe four more weeks."

Human and horse cases are diagnosed and tracked whenever they occur, she says. And because there were so many more cases this year than in previous years, "we do expect to see a few more humans and horses" infected.

Meanwhile, the most recent count of the virus from the state health department found the virus in more counties statewide. From Sept. 12-16, the most recent dates for which information is available, there were 13 new human cases diagnosed, and the virus was confirmed in 22 more horses, four more dead birds, six more mosquito pools and six new sentinel chickens.

There are now 38 human cases confirmed (two of those were found during routine screening of donated blood and were detected before the blood was given to anyone).

But Wyman said the number of human cases is clearly an undercount for a variety of reasons. Most people who are infected have no symptoms or mild ones. It is most likely those with severe fever or neuroinvasive symptoms like meningitis and encephalitis who get tested. That's borne out by the fact that almost half of the total confirmed human cases are classified as having produced the more serious neuroinvasive symptoms. Since that is believed to occur in one of 150 cases, that would mean that more than 2,000 Utahns have been infected with the virus, although most of them didn't know it.

The death toll remains at one, a Uintah County man who died from West Nile virus complications earlier this month.