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Why is virus killing only Mexicans?

Experts say flu's mutation, genetics could be factors

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OTTAWA -- As they continue to analyze the new swine-flu virus, researchers are grappling with a puzzling question: Why are the Can­adian and U.S. cases milder than those in Mexico?

It's not just an interesting question for scientists to ponder. Over the com­ing days and weeks, public-health of­ficials will be watching like hawks to see if the milder cases are a sign the outbreak is dissipating, or whether such cases are just the prelude to a full­blown pandemic.

Infectious-disease experts note the Spanish flu pandemic started out mildly in the spring of 1918 before re­emerging with a vengeance in the fall.

"We cannot be complacent, because this particular influenza strain, just like any other virus or flu strain, can still continue to mutate and it can mutate in either direction," said Dr. Colin Lee, as­sociate medical officer of health at the Simcoe Muskoka District Health Unit.

There have been more than 150 sus­pected deaths in Mexico.

On Wednesday, the United States an­nounced a toddler from Mexico City had died after catching the swine flu.

To date, most of the cases in countries other than Mexico have been relatively mild. Several theories are emerging to explain the discrepancy.

One is purely statistical.

In any flu outbreak, there will be a large number of mild cases and a much smaller number of severe, or even fa­tal, cases. Given that Mexico is the epi­centre of the outbreak, it makes some sense more deaths would have been confirmed there so far, noted Dr. Ger­ald Evans, chief of the infectious-dis­eases division at Queen's University.

Experts also say the virus could have mutated, becoming milder as it mi­grates to other parts of the world.

It's also possible the strain found in places such as Canada and the U.S. is at an earlier stage of mutation than the original strain in Mexico, which would suggest Canada and the U.S. are in store for much more serious cases.

"The question really is are we look­ing at the earlier stage of the disease, which means the strain we are seeing now (in Canada and the U.S.) is just an earlier version of the Mexican strain," said Bhagirath Singh, scientific direc­tor of the CIHR Institute of Infection and Immunity at the University of Western Ontario.

There is also the possibility some­thing in the genetic makeup of Mexi­cans is making them more susceptible, although some experts dismiss the hy­pothesis.

"We do not differ genetically that much from our Mexican brothers and sisters as some people might speculate, and genes very rarely have anything to do with the expression of infectious dis­eases," said Evans. Some point to poor health care in­frastructure in some parts of Mexico, which would make it more difficult for some Mexicans to receive care, or even air pollution in Mexico City.

"This is a respiratory disease, and in parts of Mexico, especially Mexico City, there's a lot of pollution, and it may exacerbate respiratory infec­tions," said Lee. It will likely be weeks before re­searchers have a solid hypothesis.

"The Mexican data may not be very reliable because of their testing and healthcare infrastructure, so they may not be seeing the milder cases," Lee. "It's so early right now that nobody has really confirmed the data."

-- Canwest News Service

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