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...