West Nile virus hasn't hit N.C.

This is a time that once stirred fear in North Carolina: the beginning of West Nile virus season.

Four years ago, the mosquito-borne disease killed two people in the state and sickened two dozen others. Many thought it was a growing public health threat. But ever since, the viral illness has left North Carolina mostly unscathed, even as it continues to claim hundreds of lives around the country.

Already this year, 54 human cases have been reported nationwide, according to the Centers for Disease Control and Prevention. California is preparing for its deadliest year ever.

Only one human case, however, is on the East Coast, in Virginia. A disease that first appeared along the Atlantic coast is now largely a scourge of the west. And North Carolina researchers and health officials are left with a mystery: What ever happened to West Nile virus?

"We thought we were at the beginning of an epidemic," said Jeff Engel, the state epidemiologist.

Instead, Engel has watched as West Nile dipped from 24 cases in 2003 to fewer than five each year since, none fatal. Last year, only one North Carolina resident was sickened.

Meanwhile, other mosquito-borne diseases have stayed constant. Just this week, a 3-year-old girl in Buncombe County came down with the year's first case of La Crosse encephalitis, a disease that affects about 25 people a year, usually in the western half of the state. It kills about 1 percent of those who contract it. North Carolina also still sees about one case every other year of eastern equine encephalitis, which kills half of those who get it.

Little-known virus

Scientific theories for West Nile's march westward abound. But most admit that the virus is still not well understood. It appeared in the United States only eight years ago, when it killed seven people in New York and began moving south. It still kills a handful of people on the East Coast each year.

Scientists do know, however, that the disease depends on a relationship between birds and mosquitoes. In order to sicken humans, mosquitoes must feed on infected birds and then bite humans.

Nolan Newton, head of the state's public health pest management section, said some scientists have postulated that, after a few years, all the most susceptible birds die off and those that remain have resistance to the disease.

A Cornell University study released this spring bolstered that theory, finding that West Nile had ravaged some birds -- including crows, chickadees and blue jays -- that once flourished in the United States.

Bird die-off not seen

In North Carolina, however, experts say they never saw evidence of a mass die-off of birds.

John Gerwin, an ornithologist at the state Museum of Natural Sciences, said he never got reports of scores of dead birds, even at the disease's peak, when the state was asking people to report every dead bird they found.

"If a bunch of birds did die, we just didn't find them," Gerwin said.

The state no longer tests dead birds for West Nile virus, because it lost federal funding for the program. Engel said the only money the state still receives is for testing of humans in cases where the virus is suspected.

Charles Apperson, an entomologist at N.C. State University, said he thinks it's more likely that North Carolina isn't home to the right kind of mosquitoes. Though mosquitoes abound here, Apperson said most aren't the type that feed on both birds and humans.

He said other states that have suffered far worse with the disease -- such as Colorado, where 76 people have died since the virus first emerged, or Texas, where 101 have died -- have large populations of the types of mosquitoes that feed on both.

That theory, however, doesn't explain the 2003 spike in North Carolina.

The only thing researchers know for sure is that they can't predict what West Nile will do next. All said they wouldn't rule out more scattered deaths from the disease.

And Newton, the state pest management expert, said the recent drought has turned some ponds into small, stagnant pools -- favorable conditions for the type of mosquitoes that often transmit West Nile to humans.

"We shouldn't let our guard down," Newton said, "because the mosquitoes are still out there."