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Fri Nov 17, 2000 - Updated at 09:21 AM

Mathematicians work on ways to wipe out measles

Formula an offshoot of bid to save endangered species

Peter Calamai
SCIENCE REPORTER

OTTAWA - David Earn is seeking a mathematical formula to help wipe measles and other infectious diseases off the face of the Earth.

That formula might say it's best to vaccinate everyone who hasn't already had a measles shot at the same time every year, rather than the current practice of vaccinating children at 13 months.

Such a practice could synchronize the ebb and flow of measles so that epidemics and low-disease periods occurred everywhere at the same time.

``That policy gets a bigger impact for the same resources, because during those low periods the disease may simply burn itself out'' says Earn, a mathematics professor at McMaster University.

Such a detailed scenario is still only speculation right now but Earn and two fellow researchers take a major step toward that goal in an article published today in Science magazine.

At first glance, the Science article seems unrelated to better vaccination strategies. It lays out mathematical rules to ensure that proposed schemes to save endangered species don't instead hasten their extinction.

Earn explains that the same complex math applies to forecasting the dynamics of widely different natural populations, ranging from the measles virus to endangered species like the Florida panther.

``Eradicating infectious diseases is just the opposite of saving an endangered species,'' he says.

But the endangered species case is mathematically simpler than infectious diseases, so the researchers tackled it first. They are now adapting the approach to make the measles vaccination more effective.

``We understand the most about how measles spreads in the population and what has caused changes in the pattern of epidemics over the past century,'' Earn says. He added that measles vaccine provides nearly 100 per cent protection from infection.

The equations published today allow ecologists to predict whether it's wise to open a corridor between isolated groups of a threatened species. Rudimentary corridors have already been cut for Florida's vanishing panther and for elephants in India.

But opening such corridors might synchronize population fluctuations among the endangered species in the previously separated areas, actually making them more vulnerable to extinction than before.

Earn and colleagues Simon Levin of Princeton University and Pejman Rohani of Cambridge University conclude that this potential danger can be avoided by determining the dispersal pattern of the species - with and without corridors - and the maximum offspring in a season.

These values are then plugged into the new formulas which forecast the impact of building the corridors.

This new tool was welcomed by an expert who studies animals whose habitat has become fragmented.

``We're not 100 per cent sure that corridors are always a good idea,'' says André Desrochers, a behavioural ecologist in the forestry faculty at Quebec's Laval University.

 

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