January 14, 2004 – University of Alberta researchers have developed the first model to predict risk of West Nile virus in North America--a tool that could help prevent the infectious disease from becoming an outbreak.
Dr. Marjorie Wonham and her fellow researchers from the Centre for Mathematical Biology at the U of A, created a simple mathematical model using dead bird counts collected in New York in 2000. Their research is published in the current journal issue of the Royal Society of London Proceedings. Graduate student Tomas de-Camino Beck and Dr. Mark Lewis, director of the Centre for Mathematical Biology, are co-authors of the paper.
West Nile virus is an emerging infectious disease in North America that spreads primarily through contact between birds and mosquitoes. It can be lethal to birds, horses and humans. One of the U of A group's key findings is that the chance of an outbreak is decreased by removing mosquitoes, but is actually increased by removing birds. The model provides a new analytical method for determining necessary mosquito control levels.
"This virus is endemic and we're probably never going to get rid of it completely unless we say that we're going to kill all the mosquitoes in the world--that's not going to happen," said Wonham. "What this work does is tell you just what percentage is necessary to keep the virus below an outbreak."
The research group set up parameter values from published scientific papers on mosquito biology, crow biology and West Nile biology. In order for a specific region to use this model, officials could tailor such parameters as mosquito life span, biting rate and crow life span to the data in their area. For example, since Edmonton summers are short and dry, the mosquito life cycle might be quite different than in the longer, more humid summer of New York.
Currently mosquitoes are killed through the application of chemical larvicides to the water, filling in the wetlands to remove the habitat and as a last resort, spraying chemicals to kill the adult species.
"Since applying chemicals and filling in wetlands cost money and cause environmental damage, one would ideally use the minimum amount of control that would still be effective in preventing outbreak," said Wonham. "Our model lets you calculate the threshold mosquito population for West Nile outbreak--you just have to keep them below the threshold level. This means, we would hope, minimal economic cost and environmental damage while still preventing outbreak."
Mathematical models have been used to manage other diseases such as malaria but this is the first to focus on the West Nile virus. Wonham was supported in the project through Killam post-doctoral fellowships and the National Sciences and Engineering Research Council of Canada (NSERC), while de-Camino Beck was funded as a U of A biology graduate student, and Lewis was supported through grants from NSERC and the Canada Research Chair.
Related links – internal
The U of A Centre for Mathematical Biology website: http://www.math.ualberta.ca/~mathbio/
Dr. Marjorie Wonham's U of A webpage: http://www.math.ualberta.ca/~mwonham/
Dr. Mark Lewis's U of A webpage: http://www.biology.ualberta.ca/faculty/mark_lewis/
Tomas de-Camino Beck's U of A webpage: http://www.ualberta.ca/~tomasd/
Related link – external
The Royal Society of London Proceedings Journal website: http://www.pubs.royalsoc.ac.uk/proc_bio_homepage.shtml