OKLAHOMA CITY —
Despite a wetter than normal spring and early summer, there has yet to be a reported human case of the potentially deadly West Nile virus, according to the Oklahoma State Department of Health.
The first mosquitoes of 2013 to be confirmed in Oklahoma as carrying the virus were found in Tulsa County, the Tulsa Health Department reported Thursday.
There had been eight confirmed cases of the disease in Oklahoma by the end of July 2012, and more than 30 by mid-August, on the way to a record number of 178 cases for the year. Fifteen of those people died, also a state record.
Culex mosquitoes, which tend to thrive in stagnant water, contract the virus from infected birds and pass it along to humans through their bites.
The virus also tends to run in cycles, said state Health Department epidemiologist Laurence Burnsed, and the reason for that has proved difficult to pinpoint.
“The last two years in which we had a high number of cases, it was followed by years of not as many cases,” Burnsed said. “Bird populations can decline, reducing the number of infected mosquitoes.”
The virus was first recorded in Oklahoma in 2002 with 15 cases, jumping to 79 cases in 2003. The number fell to 19 in 2004 and rose to a then-record 98 cases and nine deaths in 2007. The numbers then dropped to nine cases in both 2008 and 2009.
An average of 5.11 inches of rain fell across Oklahoma during July, 2.37 inches more than normal to make it the 15th-wettest July since record-keeping began in 1895, according to the Oklahoma Climatological Survey.
The amount of rain and the generally consistent rainfall may have played a role in keeping the mosquito population down thus far, said Bruce Noden, a professor of public health and veterinary entomology at Oklahoma State University.
“If you’ve got water hanging around for three or four weeks, two months, it becomes a breeding site. But if that water level is changing, moving, it changes the nutrients and the habitat” of the mosquito, Noden said.
The West Nile virus season is considered to be May through November in Oklahoma, with the greatest risk from July through October, according to the Health Department.
Symptoms of West Nile virus include fever, headache, dizziness and muscle weakness. Long-lasting complications can include difficulty concentrating, migraine headaches, extreme muscle weakness and tremors and paralysis.
Measures to avoid the disease include using an insect repellent containing DEET when outdoors; eliminating standing water from items such as buckets, pool covers, tires and gutters; and changing pet water dishes daily.
“We are still in the middle of a typical season, and people need to remember those preventive measures and follow them,” said Burnsed.