Monday, June 8, 2009

Mosquitoes and Fevers

As the rainy season approaches I have noticed that the Asian Tiger Mosquito, that striped flying monster which is the carrier or vector for both chikungunya and dengue, is increasing in number and range. Research also suggests that climate change is assisting the spread of this mosquito in many parts of the world.

And the chikungunya virus keeps mutating. We already know that the last Indian Ocean outbreaks were caused by a different strain of the virus. This strain differs from those involved in earlier outbreaks and makes the virus more likely to enter the cells of the Asian Tiger Mosquito and replicate after the insect has fed on the blood of an infected person. In fact, the symptoms are also changing. At a meeting of WHO last month it was suggested revising the definition of chikungunya fever because researchers have noticed the symptoms have changed.

This points to the fact that there needs to be timely and better identification of fever cases. But for prevention there needs to be early warning systems set up in countries like Seychelles. In La Reunion, where the chikungunya outbreaks caused massive health, economic and social problems, a surveillance system is now in place. This collects information on the mosquito density in every area which is then used in scientific models to predict where the next outbreak might occur. The system gives citizens and government advance warning.

The mosquito density is only a possible indication of the presence of the chikungunya virus and not a certainty, but it does give an advance warning for early action. In some countries better early warning systems especially based on gis (geographical information system) are under development. gis -based modeling can predict chikungunya-prone areas using information on the distribution of the mosquito vectors, rainfall, temperature, altitude, vegetation cover and urbanization.

More sophisticated data such as on the mosquitoes’ ability to transmit the disease and the susceptibility of people in different parts of the country can also be used in GIS-based models to predict the spread of the disease and help pinpoint the time when an outbreak could become an epidemic.

In Seychelles such GIS based modeling would be very useful. Both Dengue and chikungunya cause huge hardships, loss of productivity and losses of millions of Rupees. The country does have a GIS unit with good GIS maps. Perhaps donors should be approached to assist with setting up with a GIS-based early warning system. Putting this in place is not as simple as it sounds but is greatly needed because early action based on early warning is critical in preventing an epidemic.

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