U.S. poised for epidemic West Nile year
By Amy Cox
CNN
(CNN) -- With summer waiting around the corner and mosquitoes beginning to buzz, the United States is poised for a third epidemic year of West Nile virus, experts warn.
"We had a huge epidemic in 2002 and we told everybody that this is the biggest epidemic [of its kind] ever to occur in the Western hemisphere -- and then the next year we have an equal one," said Dr. Anthony Marfin, an infectious disease expert with the Centers for Disease Control and Prevention in Fort Collins, Colorado. "Our concern is that it's going to be like this every year."
Dr. Daniel Blumenthal, head of community health and preventive medicine at the Morehouse School of Medicine in Atlanta, Georgia, agreed that the threat level this year most likely would be about the same as the last couple of years, but because of uncertainty surrounding the virus, "I would expect the unexpected this summer," too.
In 2003, human cases in the United States exceeded 9,800, more than double the previous year's 4,156, according to the CDC. Blumenthal said the sharp jump in cases may be due to better recognition of West Nile as an illness -- not necessarily an increase of actual cases. The death toll, however, didn't change dramatically: 284 in 2002 compared to 262 in 2003. Blumenthal explained that unlike illnesses which can escape detection, a death is thoroughly investigated, which may be why the death toll remained steady.
By last year, all but three states -- Oregon, Alaska and Hawaii -- had experienced either human cases or animal infections. The Western states were reporting low numbers. But that may change this summer.
Western states wary
Some say California is the potential hotspot for the virus this season. Last year, the state reported only three people sick from the virus, but the heavy use of irrigation by agricultural areas combined with the prevalence of standing, polluted water in cities creates prime breeding grounds for different types of West-Nile carrying mosquitoes, according to entomologist Dr. John Edman.
"We certainly have all the ingredients here in California for a major outbreak that involves two or three different species of mosquitoes, where a lot states may have just had to worry about one," said Edman, a researcher at the University of California, Davis, and director of the school's Center for Vectorborne Diseases.
But Edman said California has one of the most aggressive mosquito surveillance and control programs in the country. That, coupled with the years of advance warning about West Nile, may help the state fend off a large outbreak that some states, such as Colorado, have faced. Last year, Colorado reported almost 3,000 human cases, more than a quarter of the entire country's case tally.
"[West Nile in California] could be worse than last year's Colorado. It could also be not as bad," Edman said. "But I don't think there's any question we're going to see more than three cases this year. Whether we see 30, 300 or 3,000 -- I don't know."
Once the virus becomes entrenched all across the country, some researchers believe West Nile outbreaks in the future will develop a cycle of dying down every few years and then suddenly flaring up for one season.
"I think we'll see a lot of oscillation from year to year in the future, compared to what's happened in this original spread across the country," Edman said. "But I don't see it just dissipating and going away and being so unimportant that we don't have to worry about it anymore."
The fight against the mosquito bite
The virus, first identified in 1937 in the West Nile region of Uganda, spread to the United States five years ago. The primary transmitters of the virus are mosquitoes, which become infected by biting infected birds, the natural host of the West Nile virus. In turn, the mosquitoes can infect humans, animals and uninfected birds with their bites.
 West Nile has been found in more than 130 species of birds since an epidemic in the New York area killed large numbers of crows in 1999. |  |
The CDC reports that most infected people never show any signs of the illness, but about 20 percent may experience flu-like symptoms such as fever, headache and body aches. In a small number of cases, the virus causes sometimes-fatal West Nile encephalitis or meningitis (inflammations of the brain or of the membranes around the spinal cord and brain).
Currently, there is no vaccine for West Nile, and the CDC's Marfin said the several drugs in development are still years away from approval. Prevention remains pivotal, he said.
"One of the things we really have to impress upon people is that it is never good to be fed on by a blood-sucking insect," Marfin warned. Fixing window and door screens so mosquitoes don't enter the house, wearing long-sleeved shirts and pants outside, and using mosquito repellents that contain DEET are steps the public can take, he said.
Even if mosquitoes bite, the risk of a person contracting the virus is low. According to government figures, only 1 percent of mosquitoes carry it in areas where the virus is established. And less than 1 percent of people bitten by those mosquitoes ever develop serious symptoms that would lead to death. By comparison, about 36,000 Americans die from the flu and flu-related illnesses each year.
"I don't think people should be unduly alarmed," Blumenthal advised. "They should try to keep the mosquito population down in their own back yard ... but I don't think they should lose sleep over it or lock themselves in the house because they're afraid to go out and expose themselves to mosquitoes."
