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FACING an invasion? Posting a line of guards along your border is a good
idea. That’s exactly what Canadian health authorities are doing—except
their sentries will be chickens, dispatched to the country’s southern border to
serve as an early warning system in case West Nile virus moves up from the
US.

Although West Nile virus mainly infects birds, it can be transmitted to
humans by mosquitoes. Infected people—especially the
elderly—occasionally develop encephalitis. Last summer, the virus struck
New York City, making 46 people ill and eventually killing seven, and as a
result, the city spent an estimated $10 million on controlling
mosquitoes. No human infections have been reported since last summer, but the US
Centers for Disease Control and Prevention announced in March that the virus had
been found in mosquitoes overwintering in New York. So a new outbreak may yet
occur this year.

The virus probably travelled to New York in an imported exotic bird. Although
the virus has yet to move north to Canada, the Canadian health authorities plan
to catch it in the act if it does. “We are going to be putting out sentinel
chicken coops from Saskatchewan to Atlantic Canada,” says Harvey Artsob, chief
of zoonotic diseases at Health Canada’s Laboratory Centre for Disease Control,
Ottawa. There will only be a few chicken coops in each province, so the sentinel
chickens will be thinly spread along about 2500 kilometres of border. “It’s a
big country,” Artsob notes.

Because the virus doesn’t cause any symptoms in chickens, the sentinels will
be tested once a week for a viral antibody. Dead birds found in the wild will
also be tested.