Ponds and catch basins are common mosquito breeding grounds
In mid-April 2004, a man in Ohio became the first person that year to contract the West Nile virus in North America. Around the same time, provincial health authorities began to unveil their strategies for fighting West Nile in 2004.
For the first time, officials in B.C. announced their strategy for West Nile. The spread of the virus was thought to have stopped at the Rocky Mountains, but cases cropped up in California in 2003.
Dr. Murray Fyfe of the B.C. Centre for Disease Control said the virus could come over the Rockies or be carried up from California by migrating birds.
B.C.'s strategy involves identification of mosquito breeding grounds and a public education campaign. Captured mosquitoes and dead birds were also tested for the virus.
The Yukon Territory followed B.C.'s lead with a similar strategy days later.
The Manitoba government asked people to report dead crows, blue jays, magpies and ravens to a special hotline. The birds were tested to track the spread of disease.
Public health authorities in Quebec announced a plan that would see more areas being sprayed with larvicide, but the spraying may be delayed until later in the summer. The provincial health minister said the effectiveness of spraying earlier in the spring is still in question.
In the end, though, there were only 25 confirmed human cases of West Nile in Canada, compared to nearly 1,400 in 2003. While health officials gave some of the credit to larvicide and blood screening programs, they admitted the cool, wet summer kept mosquito activity low and curbed the spread of the disease.
In 2003, different parts of the country debated how best to guard against the spread of West Nile.
Toronto announced on May 7, 2003, measures to fight West Nile virus. It established an information hotline and a website. Toronto also applied a pesticide called methoprene to kill mosquito larvae in 175,000 catch basins. Public health officials acknowledged the concern in some quarters about the environmental effects of methoprene.
"I do want to emphasize that although it is classified as a pesticide, it is amongst the least toxic of those that are registered for use, and in Canada, only methoprene is registered for use in catch basins, and catch basins are the primary focus for breeding of the Culex pipiens mosquito," said Toronto Medical Officer Sheela Basrur.
Cities across Canada debated over how best to fight the yearly mosquito invasion, whether to spray, and if so with what.
Watch Heather Hiscox's report (Runs 4:12)Winnipeg
Some regions opted for a new weapon of choice in the war against West Nile, a biological larvicide called B.T.I. It's a bacterium from the soil that destroys the stomachs of the larva in minutes and it's harmless to other aquatic life.
"It's the least dangerous with the less impact on the environment and with no impact on human health," said Paul Maloney, who is helping kill mosquito larva in Quebec.
Quebec sprayed B.T.I. as part of an aggressive plan to combat West Nile, for the first time attacking early before the mosquitoes breed. Ontario has a similar strategy. Even the five provinces that hadn't yet seen West Nile braced for its arrival, planning careful surveillance of mosquitoes and dead crows.
But nowhere was West Nile a greater priority than Winnipeg, a city of 10,000 potential hot zones.
A truck spraying the streets of Winnipeg
"We want to be on the cutting edge of mosquito control," said Jenny Gerbasi, a Winnipeg city councillor.
They invested heavily, applying larvicide more often from the air and the ground "with the sole purpose of trying to control mosquitoes without having to resort to residential fogging," according to entomologist Randy Gadawski.
Fogging, or spraying a fine mist of pesticide in to the air, kills adult mosquitoes. In the summer of 2002, after four dead crows tested positive for West Nile, trucks rolled in to a Winnipeg neighbourhood and began spraying malathion, a chemical linked to cancer and neurological disorders.
There are some scientists who believe cities should fog in the spring to kill adult mosquitoes as they emerge from their winter sleep, but many are convinced the health risks of pesticide still outweigh the risks of West Nile.
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External Links
- West Nile Virus Surveillance Program
- West Nile Virus, Public Health Agency of Canada
- World Health Organization
- Centres for Disease Control
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Quick Facts
According to the U.S. Centers for Disease Control:
Family: Flaviviridae
Genus: Flavivirus Japanese Encephalitis Antigenic Complex
Complex includes: Alfuy, Cacipacore, Japanese encephalitis, Koutango, Kunjin, Murray Valley encephalitis, St. Louis encephalitis, Rocio, Stratford, Usutu, West Nile, and Yaounde viruses.
Flaviviruses: share a common size (40-60nm), symmetry (enveloped, icosahedral nucleocapsid), nucleic acid (positive–sense, single stranded RNA approximately 10,000-11,000 bases), and appearance in the electron microscope.