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10-09-2012 | Article

Texas battles to dent mosquito population as West Nile cases approach 2K


Free briefing transcript

medwireNews: Texas has taken to the air in the fight against the West Nile virus (WNV).

As of September 4, WNV activity in humans, birds, or bugs has been reported in every state except Alaska and Hawaii. Texas, the state hardest hit, has been bombing heavily affected areas with aerial pesticides, resulting in substantial reductions in populations of WNV-carrying mosquitoes, health officials report.

"As we expected, the number of human cases of West Nile virus disease continues to rise in the United States. We expect this increase to continue for the next several weeks, probably until October," said Lyle Petersen, director of the Centers for Disease Control and Prevention (CDC) division of vector-borne infectious diseases in a briefing.

"As someone who was sickened with West Nile virus infection several years ago, I can personally relate to the people's concerns about getting this infection. Through the combined efforts of federal, state, and local public health departments, we're working to prevent the spread of infection," he added.

So far this year, a total of 1993 human cases of WNV infection have been reported from 44 states, and 87 deaths attributable to the virus have been reported to the CDC. Slightly more than half of all cases (54%) were classified as neuroinvasive disease, causing encephalitis or meningitis, and 46% were determined to be non-neuroinvasive.

Based on previous WNV epidemics, the CDC estimates that the current outbreak may have peaked in mid-to-late August, but that the number of reported cases will continue to rise over the next few weeks because of the latency period between infection, development of symptoms, and diagnosis.

"Even if West Nile virus transmission were to stop today, we would continue to see reports of cases for several weeks," Petersen said.

Hurricane Isaac and the copious amounts of rain dumped on some of the areas at the epicenter of the epidemic are not expected to significantly increase mosquito populations or the transmission of the virus, Petersen said. A small increase in WNV cases in Gulf Coast states following Hurricane Katrina in 2005 may have been related to extra exposure time among people who lost their homes during that cataclysmic event.

David Lakey, commissioner of the Texas Department of State Health Services, said that in areas where the weather allowed two consecutive aerial sprayings, there was a 93% reduction in WNV-carrying mosquitoes.

By Neil Osterweil, medwireNews reporter