September 15, 2005
sources: Sripps-Howard wire, interviews, personal communication
CLOUDS OF MOSQUITOES OF "BIBLICAL PROPORTIONS" are rising from stagnant waters left by Katrina, Janet McAllister, a Centers for Disease Control entomologist on site, told Scripps-Howard news service Tuesday. Two C-130 Air Force reserve planes flying out of an air field in Duke, Fl. began aerial spraying of eastern New Orleans with the organophosphate Naled (dibrom) yesterday, to knock down the adult mosquito population. The mosquitos now in New Orleans are not primary West Nile carriers, but they pose such a nuisance that power line workers have been unable to work. Inland, populations of the ubiquitous Culex quinquefasciatus, or Southern house mosquito, which is a primary West Nile vector, are rising astronomically. In one undisclosed mosquito-control district, the number of trapped mosquitoes has increased 800 percent over pre-Katrina levels, the CDC's McAllister said.
CDC acknowledges the danger of a West Nile epidemic. "We're in uncharted territory," said Dr. Lyle Petersen, director of the CDC lab in Fort Collins, Colo. "We've never had a hurricane hit when there was a lot of West Nile virus activity happening at the time, so we're not quite sure what's going to happen." The danger is the huge increase in mosquitos and the huge increase in the number of people exposed outdoors. There have been 62 reported human West Nile cases this year in Louisiana and Mississippi. That is without an epidemic. The fatality rate is 5 to 15 percent, much higher in the elderly. Mosquitoes which survived Katrina can already be infected, and some new cases of West Nile have begun to show up. The huge new populations just beginning to fly will take 7 to 10 days from the time they first bite an infected bird to become viremic, says Dr. Roger Nasci of the CDC entomology division. Thus the window for an epidemic opens within the next two weeks. It persists at least until early to mid-October, when the cooler weather should reduce the population of Culex. However, other species capable of carrying the virus survive into colder weather, and under the present conditions, no one knows what damage they can do.
Matt Yates, director of East Baton Rouge Parish mosquito control program, reports that the area north of Lake Pontchartrain is very infested. Some of the parishes there have spray planes flying and are contracting help from outside aerial sprayers. But only 20 parishes in Louisiana have organized mosquito programs. Much of the delta area south of New Orleans is still under water. The Baton Rouge metropolitan area (population 413,000) has 250,000 refugees, conservatively estimated; some say 500,000. People are camping out everywhere. According to {Science} writer Paul Driessen, the Air Force C-130s can spray 60,000 acres a day (=94 square miles). The area stricken by Katrina is 90,000 square miles. "I've never seen anything like this," the CDC's McAllister said. "I can only imagine this is what Europe looked like after World War II. There are displaced people everywhere, and there are huge camps of responders everywhere, living in tents. So we've got huge numbers of people ... that can't get away from the mosquitoes." [lmh, clc]