August 15, 2003

 

 West Nile virus warning system - August 15, 2003

Posted on August 1, 2003
 

Scientists set out to build a West Nile virus warning system

To develop a warning system for potential West Nile virus outbreaks, researchers at Cornell University's Northeast Regional Climate Center and Department of Entomology are spending this summer collecting climate and mosquito data in areas where potential virus-carrying mosquitoes lurk.

If all goes according to plan, the research will result in the first Web-based simulation model that public health officials can use to determine when infected mosquitoes go on the prowl. The information is expected to be online by next summer.

"Scientists, whether they are climatologists or medical entomologists, have never fully examined the relationship between climate and the proliferation of the mosquitoes that carry West Nile virus," said Arthur DeGaetano, PhD, director of the NRCC.

Dr. Mike Bunning, an epidemiologist with the Division of Vector-Borne Infectious Diseases at the national Centers for Disease Control and Prevention branch in Fort Collins, Colo., says that his group studied three counties last year, two in Louisiana and one in Illinois, to determine whether weather conditions were predictive of West Nile activity, but they didn't turn up a pattern. He says, however, that his group looked at a macroscopic level, and this could explain why a pattern didn't emerge.

Mosquitoes develop in microhabitats, and temperature readings taken in a water-filled container in the backyard, a favorite breeding ground for mosquitoes, are going to be different from temperature readings taken by weather stations.

"I'm very happy to see this work being done at Cornell and excited about the possible outcomes," Dr. Bunning said. "They are looking at a more microscopic level, the microcultures of mosquitoes, as they relate to weather patterns, and viral replication within those specific mosquitoes."

Cornell researchers will first gather climate data and synchronize this with mosquito microhabitat observations. These data will be related to mosquito count information through statistical analysis. And then indices will be developed for moisture surpluses, degree day-based mosquito development, and killing freezes. Finally, researchers will use these data to construct a Web simulation model that public health officials can consult to determine when West Nile risk is greatest in their area.

In early July, the Cornell researchers were monitoring temperatures at tire piles in several locations, both of tire water and ambient air. They were also taking samples and determining the developmental stage of mosquito larvae, as well as analyzing mosquito composition and population size.

"The correlation between the microclimate and data generated by weather stations will provide a valuable clue on how mosquitoes develop and age in a natural setting," comments Renee Anderson, a Cornell medical entomology extension associate. This is important, since older mosquitoes carry the West Nile virus.

Temperatures not only determine the rate at which mosquitoes age but also the rate at which the virus replicates. The researchers plan to develop models that will predict when mosquito populations peak and when viral amplification reaches a critical level, representing the greatest risk of transmission to humans.

If a warning system can be successfully built, it could work in much the same way ozone alerts work, by raising a community's concern level and encouraging people to take extra precautions to protect against the disease. This includes, for example, emptying water containers, wearing appropriate clothing, and applying insect repellant.

Dr. Bunning cautions, however, that developing such a warning system will be difficult. Many factors affect arboviruses, and determining them all will be tricky. "I am semihopeful that we can boil this down to a few (factors)," Dr. Bunning said. "But anything that can elucidate the transmission cycle within the vectors or mosquitoes will be helpful."