We are going to be putting out sentinel chicken coops from Saskatchewan to Atlantic Canada

Harvey Artsob, Health Canada's Laboratory Centre for Disease Control

Last summer, the virus struck New York City, making 46 people ill and eventually killing seven.

The city authorities spent an estimated $10m 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.

This has raised fears of a new outbreak this year.

The virus probably travelled to New York in an imported exotic bird.

The virus is spread from birds to humans by mosquitoes

Although the virus has yet to move north to Canada, New Scientist magazine reports that the Canadian health authorities plan to catch it in the act if it does.

Harvey Artsob, chief of zoonotic diseases at Health Canada's Laboratory Centre for Disease Control, Ottawa, said: "We are going to be putting out sentinel chicken coops from Saskatchewan to Atlantic Canada."

There will only be a few chicken coops in each province, so the sentinel chickens will be thinly spread along about 2,500km of border.

Because the virus does not 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.