Rapid Spread of West Nile Virus Has Health Officials Scrambling

Thousands of dead birds infected with the West Nile virus have fallen from the sky across 14 states in the South and Midwest in recent months, evidence that the mosquito-borne disease is quickly marching westward.

In fact, the speed with which West Nile is moving along bird migratory routes has surprised some public health officials, who are bracing for human infections at the same time they are scrambling to understand the myriad ways the deadly virus moves through nature and how it can be controlled.

The U.S. Centers for Disease Control and Prevention in Atlanta confirmed West Nile virus in more than 5,300 blue jays and crows this year. The first ones came from Florida in June. Then from Georgia. In the months since, the CDC has found West Nile as far north as Maine and as far west as Missouri.

Thirty-eight people contracted the West Nile virus this year, with one death in Georgia. The latest case, a man in Louisiana who frequented an area where five infected birds were found, was confirmed last week. Epidemiologists say West Nile kills about 10% of those infected, attacking the nervous system and swelling the brain.

The West Nile virus first surfaced in the United States in New York two years ago and has killed 10 people. It was transmitted by the common mosquito in the Northeast. Since then, health officials have identified two dozen types of mosquitoes that carry the disease, and one of those is thought to be primarily responsible for this year’s outbreak in the South.

That surprised some experts who didn’t think that type of mosquito could spread the disease so easily.

“I wouldn’t have expected West Nile to do well at all in the South,” said Andrew Spielman, a professor at the Harvard School of Public Health and an expert on tropical diseases. “But I’m wrong, and it’s disturbing.”

While mosquitoes carrying malaria and other diseases are killers in much of the world, the bloodsuckers are largely just pests in the U.S. Explosive infectious outbreaks do occur--in 1975 and 1976, for instance, there were thousands of encephalitis cases in St. Louis--but they are largely forgotten once they run their course.

“After those huge outbreaks in ‘76, there were intense monitoring programs done,” said Dr. Anthony A. Marfin, an infectious disease expert for the CDC. “Then we didn’t have another outbreak, and eventually people find other ways to spend money. A lot of mosquito control policies and departments fell into disarray. Now we are paying for that.”

Before West Nile hit New York, only a few states, California and Texas among them, monitored mosquito-borne diseases. This year, all but two are getting grants from the CDC to beef up West Nile detection.

There is perhaps no place where mosquitoes are tracked harder than in Houston, where the hot and humid climate of the bayou breeds 55 species of the bugs in biblical proportions.

“West Nile is going to get here soon, if it’s not here already,” said Ray Parsons, who heads Harris County’s mosquito control program. “And it’s going to be a lot more severe here than it was in New York. We have a longer mosquito season and we have a lot more mosquitoes.”

As the West Nile virus skips from state to state, Parsons’ phone has been ringing with inquiries about his program, which reaches into 248 of the county’s fetid storm sewers to identify disease-carrying mosquito pools.

Parsons’ crew traps mosquitoes by hanging a cooler of dry ice emitting carbon dioxide--what humans exhale--from the underside of a manhole cover. The mist attracts the mosquitoes. A tiny lightbulb positioned under the cooler brings them even closer to a fan, which sucks them into a mesh basket.

Martin Reyna and six other county workers pluck the traps from the sewers each day and take the mosquitoes to a lab where they are ground up and tested. Between 100 and 250 trap samples are tested each week in Houston, more than in the rest of the state combined.

“You can get up to 10,000 mosquitoes in one net,” Reyna said as he lifted a manhole cover with a pick. “But even if we get just one mosquito, it’s enough to test it. Because if it turns out to be positive [for disease], then our job is done.”

It’s an expensive job: $2 million a year to monitor and intensively spray infected areas. Parsons, a 64-year-old former Green Beret who spent his Army career in medical intelligence, is hoping to get $500,000 more next year to handle the expected arrival of the West Nile virus.

“It’s hand-to-hand combat,” Parsons said of his war with the mosquito.

Houston’s search-and-destroy mission seems to work. The city has not had a widespread outbreak of St. Louis encephalitis, which is similar to West Nile, since the early 1990s, despite the fact that the area is the nation’s hotbed for the disease.

“They’re one of the best in the country,” the CDC’s Marfin said. “Their program is very intense.”

But the unpredictable West Nile virus may prove to be a bigger challenge, Parsons said. In fact, the more health officials learn about West Nile, first isolated in Uganda in 1937, the more they realize what they don’t know.

For instance, while the Asian tiger mosquito has been found to carry West Nile, it’s unknown whether it can transmit the disease to humans. If it can, this will be a problem in Houston, where the Asian tiger is one of the biggest of the biting mosquitoes here and is hard to control.

“We’re real concerned,” Parsons said. “So much is happening with West Nile that nobody knows about. Every day, it seems, I know a little bit less.”