Hadi Dowlatabadi is looking at the effectiveness and risks of pesticide spray programs - photo by Darin Dueck

UBC Reports | Vol. 52 | No. 11 | Nov. 2, 2006

West Nile Virus: To Spray Or Not To Spray?

By Hilary Thomson

When B.C. gets hit with an outbreak of West Nile Virus (WNV), pesticide spray programs will keep us all safe, right?

It may not be quite that simple, according to Hadi Dowlatabadi, of UBC’s Institute for Resources, Environment and Sustainability and the Liu Institute for Global Issues, who is principal investigator in a three-year project to help develop more systematic public health responses aimed at preventing WNV. 

“We want to examine this issue in a comprehensive way, to understand the real risks of both the virus and spraying,” says Dowlatabadi, Canada Research Chair in Integrated-assessment Modelling and Global Change. “We want to make sure we’re protecting people who may be vulnerable to the virus, and protecting our kids and the ecosystem from pesticide contamination.” 

A bird-borne infection spread by mosquitoes, WNV was first found in North America in 1999. About 80 per cent of those infected never develop symptoms of the disease.

When they do appear, symptoms can range from flu-like to fatal. About three per cent of symptomatic patients develop meningitis with high fever, coma, tremors, paralysis and death. Survivors can be left with permanent neurological damage.

B.C. is the only temperate region in North America to have escaped WNV. But it’s only a matter of time, say the researchers. In 2005, Canada had 225 clinical cases of the illness and 12 deaths reported. In 2006, neighbouring Washington State had its first cases and Idaho had approximately 800 cases.

The UBC research team, in collaboration with the B.C. Centre for Disease Control (BCCDC) and public health authorities in B.C. and other provinces, will assess effectiveness of spray campaigns and examine pesticide risks to human and environmental health.  The team will also explore public perception of risk from the virus, spray campaigns and personal protection, such as the mosquito repellant DEET.

Working with colleagues at Carnegie Mellon University in the U.S., the team has already created a model that takes into account some of the uncertainties in spraying effectiveness, such as how spray is applied and gets dispersed; how pesticides persist in the environment; and routes of exposure for humans.

The team has also applied for funding to survey approximately 5,000 people across four provinces — B.C., Alberta, Manitoba and Ontario — to determine public risk perception and levels of awareness about WNV. In addition, researchers will produce a framework for making decisions about spraying.

“There have been numerous spray campaigns undertaken without knowing the consequences,” says study co-ordinator Negar Elmieh, UBC Bridge Program Fellow and PhD candidate in Resource Management and Environmental Studies. “We want to change that and provide data on both the risks and benefits of spraying.”

The pesticide malathion is commonly used for WNV prevention spraying. Licensed for use since the 1950s, malathion is also highly toxic to fish and can last up to 19 days in water. Although spraying does not affect healthy adults, it can harm elderly persons or those with compromised immune systems. Because of their size and poor hygiene habits, children under the age of six are at risk for receiving the highest pesticide dose.

Personal precautionary measures can be an alternative to spraying. Staying indoors at dawn and dusk, covering up and using DEET are ideally the first line of defense, say the researchers.

Health officials expect WNV to become endemic, or native, to areas of Canada south of the 54th parallel within five years.

Even so, there is no national WNV surveillance program and no centralized data available to all provincial public health authorities. Spraying is usually conducted at the municipal level. Because spraying is often an emergency measure there is little in the way of systematic application, data collection or analysis. The situation is compounded by environmental limitations, such as avoidance of waterways, making spraying a patchwork operation, capable of killing only a fraction of mosquitoes.

“We hope our findings can be used to help design interventions that are safer and more effective than those that have been possible to date,” says Elmieh, who adds that the model they are developing can be used to plan any type of pesticide spraying. “The best outcome is to use spraying as a last resort.”

Research team members are: co-investigators Ray Copes, clinical associate professor, UBC Dept. of Health Care and Epidemiology, and medical director for Environmental Health at BCCDC; Dr. Bonnie Henry of BCCDC; and Kay Teschke, UBC professor of Health Care and Epidemiology and member of UBC’s School of Occupational and Environmental Hygiene. Collaborating on the project is Elizabeth Casman, research engineer at Carnegie Mellon University in Pennsylvania.

The UBC Bridge Program is a scholarship funding and research-training program linking Medicine, Engineering and Graduate Studies to develop creative evidence-based prevention measures for public, environmental and occupational health problems.

For more information on the project, visit www.cher.ubc.ca/westnile.