West Nile Virus Spreads Rapidly in the United States

By ELIZABETH WEISE | USATODAY | AUGUST 15, 2012

West Nile virus is spreading faster than it has in years, and the pace of the mosquito-borne disease is getting worse, health officials report.

States are reporting more cases than usual, says Marc Fischer, a specialist in mosquito-borne diseases with the Centers for Disease Control and Prevention (CDC) in Fort Collins, Colo. “There’s been a lot of mosquito activity in most states” this year, Fischer says.

Texas is getting the worst of it.

Sixteen people have died of West Nile virus this summer in Texas. That’s out of 381 cases of the illness. “We’re on track to have the worst year ever,” says Christine Mann, spokeswoman for the Department of State Health Services in Austin.

Nationwide there have been at least 693 cases and 28 deaths, according to the CDC and state numbers released Tuesday. That’s up from 390 cases and eight deaths last week.

A mild winter and ample spring rains allowed the mosquito population to build up early. Heat and scant rainfall are creating stagnant water pools, which make great breeding grounds, says Michael Merchant, an entomologist at the Texas AgriLife Extension Service in Dallas.

Thirty-two states have had cases of West Nile, the CDC says.

Louisiana has had six deaths in 68 cases, Oklahoma one death in 55 cases, and Mississippi one death in 59 cases. In Arizona, there’s been one death in seven cases.

California had 23 cases, one of which was fatal, and South Dakota had one fatality in 37 cases.

It’s going to get worse, says David Dausey, a professor of public health at Mercyhurst University in Erie, Pa. He says climate change means warmer winters, milder springs and hotter summers, all of which “create a longer season for mosquitoes to breed and ideal conditions for them to survive.” That will mean more West Nile and, public health workers worry, other mosquito-borne diseases such as yellow fever, malaria and dengue fever, Dausey says.

Most people who are infected with the West Nile Virus, 70% to 80%, never know they have it. Twenty percent to 30% develop West Nile fever, with headaches, fever, joint pains, vomiting or diarrhea and rash.

Less than 1% of those infected with the virus develop West Nile neuroinvasive disease involving inflammation of the brain, spinal cord or the tissue surrounding the brain. About 10% of those will die, Fischer says. People over 50 and those with compromised immune systems are more likely to develop this form.