Tuesday, June 28, 2005

K-State Virologist Says West Nile Threat Will Peak Again in Next Few Years

By Michelle Hall

Cases of West Nile virus in Kansas horses have gone down 10 times each year since it was first found in the state, in 2002.

Sanjay Kapil, associate professor of clinical virology at Kansas State University, presented these numbers: In 2002, there were about 800 clinically sick horses in Kansas. In 2003, 80 horses were confirmed with the virus. And in 2004, the number was eight.

Kapil said if the trend holds, Kansas will theoretically see only one case this year. He said the safest assumption, however, is that the numbers will not be as bad as the first year. And although he predicts the West Nile virus in equine will most likely never be as great as it was in 2002 in Kansas, the number of affected horses may peak again in the next few years, Kapil said.

There are a number of reasons behind the sharp decline in recent numbers -- and also reasons why Kapil feels the virus will peak again, albeit with a smaller "peak."

Kapil said at first, Kansas was a "naive, unexposed population." In the first year Kansas saw the virus, it eliminated the most vulnerable animals.

"Now we are left with populations relatively less susceptible to the virus," he said.

There are also now two good vaccines for the virus, Kapil said. An annual booster is also recommended. Most horses were vaccinated during the initial "havoc" of the first year, and new foals are also being vaccinated.

When West Nile first hit the United States, many felt it was more virulent than in other countries -- veterinarians were detecting the virus in animals previously thought unsusceptible, including dogs and sheep. But Kapil thinks this nation just has a better testing system -- not that the virus was stronger.

"It's not that the virus was different, we're just better at diagnosing," he said.

In addition, at first, the public was very concerned about West Nile and sent samples in to K-State to be tested quite frequently. Now that everyone knows about the virus, they might not be as diligent about bringing samples in, Kapil said.

"It is possible submission anxiety has reduced," he said. "We've accepted it and decided to live with it."

Kapil said this lowering of public concern with West Nile can be misleading and possibly harmful since the virus can never be completely eradicated. He explained West Nile is an RNA virus, which means it doesn't make a duplicate of itself when it replicates. Instead, it makes mistakes. So, there could be a slightly different version of the virus that comes back. In addition, cases could rise when horse owners feel the "threat is over" and stop vaccinating their horses against West Nile.

Kapil said the general rule for this type of virus is that the population that has gone through the first year has natural immunity for three to five years.

"We'll never have a situation as bad as 2002, but we might have another increase in two or three years," Kapil said. He said the peak won't be as high as the first year, but there will be another peak, according to his knowledge of viruses.

"U.S. horses have probably seen the worst. But it's very judicious to keep vaccinating," he said. "We'll never be free of it. There will always be sporadic cases at low levels.