Experts on alert for West Nile peak

Health officials await confirmation of the first case of this season.
Thursday, August 21, 2003 | 12:00 a.m. CDT; updated 12:55 p.m. CDT, Friday, July 18, 2008

There is only one human case of West Nile Virus waiting to be confirmed in Missouri, a sharp decrease in the number infected at this time last year. However, the government and experts warn people to stay alert as the peak season for the virus begins.

Spread by mosquitoes, West Nile was first found in the United States in 1999 and reached Missouri last year. According to the Centers for Disease Control and Prevention, most people show no symptoms when infected. However, about one in 150 people infected will develop a severe illness, with symptoms that may include a fever and lead to a coma.

A 7-year-old girl in Putnam County, with symptoms of fever and headache in late June, will be the first human case in the state if confirmed by the end of this week by CDC. She is recovering.

At least 61 people were infected by Aug. 20, 2002, though it is difficult to give the exact number as some cases were reported later.

Karen Yates, director of the Vector-Bourne Disease Program within Missouri Health and Senior Service Department, suggested the changes in the cycle between mosquitoes and birds may result in fewer infected cases this year.

Some birds have developed antibodies to the virus. The number of birds that are most likely to contract the disease from mosquitoes, such as the blue jay and crow, has decreased. Also, there is probably less habitat for mosquito larvae across the state due to dry weather.

The numbers also have decreased in horse cases. Last year, 34 horses were infected by mid-August, but at present Missouri only has 14 cases, according to combined statistics from the health department and the MU’s veterinary laboratory. However, four of the 14 cases were reported this week.

“Horses were vaccinated during the last year. Apparently this is reducing the number of horses that are clinically affected by West Nile Virus,” said Gayle C. Johnson, associate professor of veterinary pathobiology at MU. “But we may have more cases in future months.”

The decrease doesn’t mean people are safer this year.

“We don’t know enough to make good predictions,” Yates said.

The CDC said this week that the peak time period last year across the nation for West Nile was between Aug. 11 and Sept. 21. Seventy percent of all cases had their onset during that time.

“It is still early to say whether it will be better or worse than last year, as the outbreak of the virus began in July and did not end until mid-November last year,” Johnson said.

During hot weather, the health department warns people to stay alert to mosquito bites when outdoors.

“The trends over the last couple of years across the nation are that at the latter part of the season you get the most activities related to West Nile,” said Gerald R. Worley, environmental health manager. “So we have geared up for that.”

Some new measurements the health department are taking this year include trapping mosquitoes and distributing free insect repellent and mosquito larvacides.

“By reducing the exposure and number of mosquitoes, there are hopes to offset the risk of West Nile,” Worley said.

Last year, 168 people were infected in the state and seven died.

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