Climate-based Model to Predict West Nile Virus Activity

Cornell University scientists are launching a full-scale study on the influence of climate on mosquito populations that transmit diseases such as West Nile virus (WNV) to humans. Funded by a $495,000 Global Programs grant from the National Oceanic and Atmospheric Administration (NOAA), the three-year project is a collaborative effort involving medical entomologists, climatologists, social scientists and risk analysts, as well as local and state health department officials.

“We propose to develop a system for predicting and monitoring risk of mosquito vectors, West Nile virus transmission and human health risk that will be readily usable by public health professionals for decision-making,” says Laura Harrington, Cornell assistant professor of entomology and the project’s principal investigator. “This system will provide a mechanism for early warning of West Nile virus risk and serve as a model for other existing and future vector-borne disease risks for which vectors are already present in the United States. These risks include Rift Valley fever, Japanese encephalitis and Ross River viruses.”

Arthur T. DeGaetano, Cornell associate professor of climatology and director of the Northeast Regional Climate Center, is a co-principal investigator.

To develop, refine and validate the system, researchers will focus their efforts on New York state, with the view to making the system adaptable to any region. Harrington and DeGaetano hypothesize that a few key climate factors influence and drive WNV transmission dynamics and these key factors can be modeled to accurately predict the risk of WNV transmission to people.

Harrington and Renee R. Anderson, a Cornell Cooperative Extension associate in Cornell’s Department of Entomology, will determine the effects of temperature on development of key West Nile mosquito vectors in the laboratory and under realistic field conditions. DeGaetano will develop a forecasting model based on climate to predict periods of vector and pathogen abundance and human risk. Lois Levitan, a Cornell senior extension associate and Environmental Risk Analysis

Program leader, will determine the information needs of public health and vector control professionals as it relates to risk analysis. Five public health and vector control officials from across New York state will take part in the project, along with Cornell graduate and undergraduate students.

The study will integrate and expand on data acquired during a 2003 NOAA-funded pilot study. Mosquitoes develop in microhabitats, according to Harrington. The correlation of climate data with microhabitat information provides scientific clues to how mosquito populations develop and age. Older mosquitoes are the carriers of WNV, becoming infected when they feed on “reservoir” animals, such as birds, and undergo an incubation period of the virus lasting five to 14 days. During subsequent blood meals after this incubation period, the mosquitoes inject the virus into humans and animals, where it can multiply and sometimes cause illness. Outdoor temperatures determine both the rate the virus replicates in the mosquito and the rate mosquitoes age.

While mosquitoes can live as long as three or four months in a laboratory, their life span in the wild is much shorter. Thanks to predators and pathogens, the longest the average mosquito can live is probably three to four weeks, says Harrington. During the height of summer heat, a mosquito can age and become a full adult within seven to nine days.

Previous efforts to link climate information and mosquito vector management have failed for a variety of reasons, Harrington says.

“By directly addressing and overcoming the reasons why previous models have failed, the unique group of collaborators assembled for this project will gather the data needed to build realistic, validated and effective models for predicting vector activity and human health risk,” she says.