West Nile Cases Drop

AKRON, Ohio — Health officials are puzzled over why the West Nile virus, which killed 31 Ohioans just three years ago, has been drastically reduced as a summer threat.

Some say changes in the weather and wider immunity might be the reason the number of cases in humans has dropped more than 97 percent during the last two summers, but they have no definitive answer.

“We like it,” said Dr. Marguerite Erme of the Akron Health Department about the drop in reported cases. “But as to why it’s occurred — we’re not sure.”

More than 400 cases were reported in Ohio in 2002. That number dropped to 108 in 2003, and then to just 12 last year. Eight people died in 2003, and two in 2004.

So far this year, one case has been reported in the state, in a 26-year-old man from Darke County in western Ohio. Most people infected with the virus show no symptoms at all, or only very mild ones. Symptoms include fever, headache, rash, general muscle aches and weakness, gastrointestinal distress and lymph node inflammation.

Nationwide, the number of cases dropped for the first time last year, plunging from 9,862 in 2003 to 2,539. Deaths fell from 264 to 100.

The U.S. Centers for Disease Control and Prevention have reported 25 cases and one death across the country this summer.

Ohio health officials said part of the reason for the drop could be the change in weather. The mosquitoes that spread the disease thrive on wet springs and dry summers, which were the conditions in 2002 when the virus first appeared in the state.

Although rain has been scarce in much of Ohio during the last several weeks, the spring was also dry, leading to fewer pools of standing water where mosquitoes breed.

Kristopher Weiss, a spokesman for the Ohio Department of Health, said the public’s greater knowledge of the need to avoid mosquito bites also contributed to the decline.

But Cuyahoga County Health Commissioner Terry Allan said a study of county residents in 2003 showed that although almost all knew about the virus, few took steps to prevent bites.

“They knew the risks, but they did very little to protect themselves,” he said.

Fewer than one in five used mosquito repellent, and fewer than half got rid of standing water on their property, he said.

Allan said the survey, which included blood tests, showed some people had immunity to the virus but were unaware of it. The test showed that between 2 percent and 5 percent of Cuyahoga County residents carried antibodies to the virus in 2003.

Weiss says it’s unlikely that immunity could be completely responsible for the drop. Most studies have shown that about 3 percent of the population is exposed to the virus each year, which means less than 10 percent of Ohioans would be immune, he said.

That’s “not enough to see the dramatic knockdown in the numbers that we’ve seen over the past few years,” Weiss said.

Because they cannot determine an exact cause for the decline, health officials say residents need to continue avoiding mosquito bites.

“We need to pay attention,” Allan said. “It’s hard to know when it might come back again.”

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Not contagious

The West Nile virus is primarily a disease of birds and can be spread to people by infected mosquitoes.

It is not contagious from person to person.