More Outbreaks Expected in Slow-to-Start West Nile Season

The West Nile virus season has been milder than it was at this time last year, but scientists say the worst is yet to come.

“We might be right on the cusp” of outbreaks in several regions of the country, says entomologist Harry Savage of the Centers for Disease Control and Prevention division in Fort Collins, Colo.

CDC’s tally of 109 cases of West Nile infection nationally does not reflect recently detected cases in several states. In Louisiana, health officials Friday reported 22 new cases, including two deaths. Officials in Illinois, California and South Dakota also have seen new illnesses.

“We’re just on a hair trigger here,” says Lon Kightlinger, state epidemiologist in South Dakota, where four new cases reported early last week brought the state total this year to 20. “Since then, we’ve had about a dozen more human cases under investigation,” and surveillance has been increased.

“We’re investigating (reported cases) as soon as we can and getting information out to the community, so they can know the virus is circulating.”

In Louisiana, too, “there’s been a quick uptick” just in the past few days, says Joe Dalovisio, chairman of infectious diseases at the Ochsner Clinic Foundation in New Orleans. “The season so far has been slow to start, but typically August and September is when you see cases.”

Entomologist Vicki Kramer of the California Department of Health Services says West Nile activity also has picked up there in the past week or so. Sixty-four cases in humans have been detected this year, and two people have died.

This is the second year the virus has been found in the central and northern part of the state, she says, and if a pattern seen elsewhere in which the second year brings a spike in cases holds true, “we could be hit pretty hard.”

California has awarded $9 million to 75 local agencies to beef up mosquito control services, she says, and “there’s probably going to be major aerial spraying in the Sacramento area soon.”

West Nile is a mosquito-borne virus that can cause fever, achiness and swollen glands in about 20% of those infected. In about 1 of every 150 people infected, the virus can cause encephalitis, a swelling of the brain that can cause numbness, disorientation and paralysis. It can be fatal.

In 2004, the CDC had reports of 2,539 cases of West Nile infection in people, including 100 deaths. Fewer cases have been found this year compared with the same time last summer, Savage says.

“Certainly mosquito control has gotten a lot better in parts of the country since 1999,” when the first case in the USA was found in New York, he says.

Once a person has been infected, immunity is thought to be lifelong. But Savage says relatively few Americans have been exposed to the virus, so most people are susceptible. “What we hope is happening is that more people are taking precautions” to prevent being bitten by potentially infected mosquitoes, he says. “Whenever you go to an outdoor activity now, you see people with (insect repellents) they’re applying to themselves and their children.”