Canada Ponders How Best to Stem West Nile Spread

WINNIPEG (Reuters) - Canadian health officials are studying why the West Nile virus has proliferated in the Prairie province of Saskatchewan this year, and how best to prevent its spread in years to come, a prominent entomologist said on Tuesday.

The mosquito-borne disease first appeared in Eastern Canada in 2001, but spread to the Prairies for the first time this year.

"The last chapter has not been written," said Randy Gadawski, an entomologist for the city of Winnipeg, known for its voracious mosquitoes.

"This disease continues to evolve, it continues to surprise us. What the future holds is largely unknown," Gadawski told chemical company representatives at a conference.

There have been four deaths in Canada from West Nile Virus this year: two in Ontario, one in Saskatchewan and another in Manitoba.

Saskatchewan has the highest concentration of cases, with 283, followed by Alberta with 128, Manitoba with 45 and Ontario with 36, according to the most recent provincial statistics.

That compares with 53 deaths and 2,874 cases of the disease in the United States, Gadawski said.

Many people who get the disease show flu-like symptoms, or none at all, while others become severely ill because of swelling of the brain.

Last year, 20 people in Ontario and Quebec died from the disease, while more than 400 had the disease, Gadawski said. That compares to 284 deaths in the United States from a total of 4,156 cases.

Extremely hot weather in the Prairies this summer may have helped hatch 10 times the usual numbers of the species of mosquito responsible for spreading the disease, Gadawski said.

The Culex species do not bite humans, but feed on birds, which act as reservoirs for the disease, he said. Other species of mosquitoes that also feed on mammals are responsible for spreading the disease from birds to humans, he explained.

"If it's not in the birds, it won't get to the people," Gadawski said.

Scientists have found that small numbers of Culex mosquitoes survive the frigid Canadian winters, and start infecting birds as early as April, he said.

"It can kind of jump-start the whole process."

Gadawski said Canadian tracking and testing systems have improved, helping health officials determine the risk for contracting the disease.

"We still are a little unsure of how to respond to different indicators of risk," he added.