Posted on 08/03/2002 8:00:01 AM PDT by Clive
OTTAWA - Canadian health authorities are worried an outbreak of West Nile virus infection in Louisiana, which has killed four of 58 infected people, could mean the mosquito-borne illness is changing the way it spreads.
"Something seems peculiar about Louisiana with such a large number of human cases," said Harvey Artsob, head of zoonotic diseases at Health Canada.
"It's important for us to understand why, so that all our messages of reassurance in other parts of North America still hold. What's changed in Louisiana?"
As Canadians head to summer cottages this weekend, the official government message remains that West Nile virus is rare.
While some dead birds in Quebec, Ontario and Manitoba carried the virus, no human cases have been reported.
But Dr. Artsob, the nation's foremost expert on West Nile, suspects some Canadians have been exposed to the virus, which has killed 22 people since arriving in North America in 1999.
"I think there have been people who probably were infected last year, [but] I can't guarantee it," he said yesterday, adding the government contemplated testing thousands of blood samples to search for presence of the virus.
In Manitoba, health officials are still awaiting test results of 14 individuals. Thirty people in the province were tested after they displayed symptoms similar to West Nile, but 16 have been cleared so far. Test results are not expected until next week.
This week, the Ontario government announced plans to spend $9-million to kill mosquitoes carrying the virus. Health officials urged people to remove places where mosquitoes can breed, such as standing water in birdbaths, repair screens in doors and windows and use insect repellent.
The Louisiana outbreak, which yesterday prompted officials to declare a state of emergency, is expected to surpass the outbreak in New York three years ago, which infected 62 people and killed seven.
"There is no sign that this is going to go down. This is only the beginning," said Raoult Ratard, an epidemiologist with the Louisiana Department of Health and Hospitals. "We'll probably end up with the worst outbreak."
First isolated in 1937, West Nile virus was common in Africa and Asia but not seen in North America until 1999. Experts believe this strain arrived from the Middle East. Its genetic material is "almost identical to that of a [viral] isolate taken from a dead goose in Israel in 1988," Dr. Artsob said.
Dr. Artsob said human cases are typically seen about 30 days after dead birds are found. The birds become infected after being bitten by mosquitoes that feed only on birds. The virus multiplies in the birds' bloodstreams and is then carried to humans by other mosquito species that bite both birds and humans, bridging the species gap. This cycle means outbreaks are concentrated in late August and early September.
Public health officials across the United States and Canada are concerned because the disease has erupted so early in the summer in Louisiana. "Has it gotten into a broader range of mosquito species than up in the Northeast?" Dr. Artsob wondered.
Most people who contract West Nile suffer nothing more than headaches and flu-like symptoms, but the elderly, the chronically ill and others with weak immune systems can develop fatal encephalitis, or brain inflammation.
Experts say for every one person who gets seriously ill, there are as many as 300 infected with the virus who suffer no major symptoms. Elderly people are the most susceptible to illness because their immune systems are weakest.
"Unfortunately, there is no directed therapy to this virus," said Marc Desjardins, a clinical microbiologist at Ottawa General Hospital.
"People have been trying various anti-viral agents, but there doesn't appear to be any kind of success with those. So largely, therapy revolves around supportive care. There is nothing that will specifically target the West Nile virus."
Dr. Desjardins said Ontario's plan to control larval and adult mosquitoes is wise, considering how easily once-exotic diseases can be spread via airline travel. "We can go to Africa today and then be home tomorrow from these hot zones, as they're called," he says. "So any kind of public health intervention is worth the money."
Some scientists say the West Nile virus is growing more dangerous with time. Decades ago, the strain that spread through Africa and the Middle East caused little more than a fever. But recent strains seem to cause encephalitis with more regularity, particularly in North America.
Dr. Desjardins says this may be because the virus is a "foreign" invader. "You have to keep in mind that where this virus is traditionally seen, in North Africa and the Mediterranean, there's a certain amount of exposure to it and people have a level of immunity.
"So in these populations, the virus may not present the same way as when it's introduced into an entirely 'naive' population like in North America.
"On a clinical basis, there certainly are some major differences between what we're seeing [here] and the patients that you traditionally see in the African subcontinent."
One of them. Anyone for 6 month quarentines on all travellers???
---max
Hmmm.
That wouldn't explain why the NYC outbreak -- or the outbreak here in the D.C. area, for that matter -- have been so mild.
Hmmmm....probably just some bird that few in from a Palestinian neighborhood.
It takes customs six months to check each traveler for mosquitos? You must be joking. The disease is spread by mosquitos, not humans.
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