Rather than vacuuming the grass clippings out of catch basins before adding treatments to control mosquitoes, municipalities should leave the organic waste in place, the research found.

“Catch basins are a permanent source of mosquitoes on every street. By putting in cleaned catch basins we saw an average of 20 per cent of the mosquito larvae make it to the adult stage over the duration of the study. But that number was reduced to less than 3 per cent just by leaving the organic debris in the catch basins until the fall, when mosquito season is over,” says Norman Yan, a professor in 91ŃÇɫ’s Department of Biology.

Above: An electron micrograph of the West Nile virus. Photo: Wikimedia Commons.

Yan and former 91ŃÇÉ« master’s student Stacey Baker (MSc ’08) co-authored a study published in the current issue of the Journal of the American Mosquito Control Association. They were surprised by the results of the research, conducted by Baker in 2005 on residential streets in the Greater Toronto Area.

“We predicted that S-methoprene would work better in the catch basins that had been cleaned. We found the opposite – that S-methoprene binds to organic material, which holds it in the catch basins longer so that mosquito larvae are exposed to it for longer,” says Baker.

The research may have implications not only for our comfort levels, but for disease control, says Yan. The rate and the number of positive mosquito pools have been lower in the past two years in Ontario, but it remains a problem in some areas of the United States, and warmer temperatures and a wet season could increase the risk in Ontario. The West Nile virus is not carried by all mosquitoes but it can lead to severe symptoms and even death.

Public health units in Ontario determine if and when they will larvicide based on their surveillance of the level of risk. S-methoprene, which is used in Canada only for control of West Nile virus, is still being used in hundreds of thousands of catch basins in the GTA, but there has been no thought given to the cleaning schedule, according to the study authors. The study demonstrates that scheduling both the application of S-methoprene and the removal of debris makes sense, they said, and it may be worthwhile to clean the catch basins every two years instead of annually.

“Accumulated Organic Debris in Catch Basins Improves the Efficacy of S-methoprene Against Mosquitoes in Toronto, Ontario, Canada” appears in the .

91ŃÇɫ’s , which seeks to maximize the impact of academic research on public policy and professional practice, has sent a summary of the research findings to Ontario’s public health units.

By Janice Walls, media relations officer. Republished courtesy of YFile– 91ŃÇɫ’s daily e-bulletin.

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Knowing the answer could help in the development of mosquito density and control strategies as well as improvements to the current surveillance system for West Nile virus and other vector-borne diseases that may emerge, not only in Ontario, but across the country. It could also lead to a real-time warning system and better disease management by public health agencies.

Recently awarded a $100,000 research grant from the Public Health Agency of Canada (PHAC), Zhu will conduct a two-year research project, "Modeling and Risk Assessment of West Nile Virus Transmission Under Global Warming", as part of PHAC’s Pilot Infectious Disease Impact & Response Systems Program and its Clean Air Agenda. The objective is to conduct data mining and analysis, develop models for expected mosquito density given certain meteorological and environmental conditions, and establish a set of threshold conditions and criteria that are likely to be present before and during an outbreak.

Left: Huaiping Zhu

“Part of the pilot project is related to seeing how climate change will affect the virus in Ontario,” says , a professor in 91ŃÇɫ’s Department of Mathematics & Statistics. Warmer weather makes a more conducive environment for mosquito breeding and virus incubation, and that holds true for other vectors as well. With global warming, mosquitoes are likely to expand their range and spread the virus into new areas.

In Ontario, there have been two outbreaks of the West Nile virus – one in 2003 and another in 2007. The curious thing about those two outbreaks, says Zhu, is “we didn’t have the maximum amount of mosquitoes in those years.” It seems counterintuitive that the outbreaks would occur during times when mosquitoes were not at peak levels. That, he says, may indicate that temperature and precipitation play a larger role in driving the spread of the disease than previously thought.

Zhu has the West Nile virus incidence data from the Ministry of Health & Long Term Care, the study’s collaborator, as well as the data on the temperature and amount of precipitation in Peel Region in Ontario since 2002. The first case of West Nile virus appeared in Ontario in 2001, with surveillance data collecting beginning the following year. With the data, Zhu and his research team can create models to assess the most likely scenario of when incidents of West Nile virus will surge. Once they have an idea of what is happening in Peel Region, they hope to expand the research to all of Ontario and eventually Canada. Part of the difficulty will be the narrow time frame Zhu has to work with each year – 16 weeks when mosquitoes are active in Ontario.

The preparation of the data has already been done using 91ŃÇɫ’s Laboratory of Mathematical Parallel Systems (LAMPS) as part of Zhu’s 2007 Ministry of Research & Innovation research project, "Modeling, Surveillance, Prediction and Control of West Nile Virus in Ontario". LAMPS is a high-power parallel computing lab in the Department of Mathematics & Statistics, which Zhu, along with 91ŃÇÉ« Professors Steven Wang and Zijiang Yang, set up using a $250,045 grant from the Canada Foundation for Innovation and a matching grant from the Ontario Innovation Trust.

Zhu now needs to design models to plug the data into, which will hopefully tell him more about how the virus is spread to birds and the optimum temperature and amount of precipitation needed for an outbreak to occur. Another, part of the equation is mosquito reproduction and how that fluctuates with the weather. Then the information will need to be analyzed.

The whole idea, says Zhu, is to discover “what are the conditions that are needed to cause the West Nile virus.” To do this, it’s imperative to understand how the climate influences the host. “Only when this is clear, can we go on from there,” he says. Then they can begin to understand some of the other variables, such as how different landscapes affect mosquitoes across the country, what their preferred habitat is and whether it is true for all species of mosquito, and how the rate of evaporation plays into the equations.

“For that part it is more complicated,” says Zhu. “So depending on the results from the first part, we will know if it will be possible to develop it into a larger project taking into account those other factors.”

Although West Nile virus was first isolated in Uganda in 1937, it has progressively spread to Egypt, Israel, South Africa, Europe and North America.

By Sandra McLean, YFile writer

Reprinted courtesy of YFile, 91ŃÇɫ’s daily e-bulletin.

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