Weather patterns tied to disease outbreaks

LONDON - Doctors hoping to predict disease outbreaks may want to tune in to more weather forecasts. Weather patterns can be a key factor in finding out when an epidemic is imminent, because they determine the conditions for germs and their carriers to breed.

This can help quicken the response to viral outbreaks worldwide and health disasters such as Europe’s devastating 2003 heat wave. Global warming is adding urgency to such strategies for fighting disease.

Health officials were able to reduce the effects of an outbreak in Kenya of Rift Valley fever, a deadly hemorrhagic fever, after NASA scientists noticed exceptionally warm sea temperatures and elevated rainfall in East Africa four months ago.

When flooding in Kenya ensued, NASA climate specialist Assaf Anyamba was certain the elements were in place for an outbreak namely, ideal breeding conditions for the mosquitoes that transmit the disease.

“By the end of October, this outbreak was pretty much a lock,” he said.

Mr. Anyamba and his colleagues at NASA and other agencies track climatic factors that influence disease outbreaks, including levels of precipitation, atmospheric moisture and vegetation. The information is passed to organizations including the World Health Organization (WHO) and the Food and Agriculture Organization, which relay it to the affected countries.

The last major outbreak occurred in Kenya in 1997 at exactly the same time of year and killed about 400 people. The response was so slow that by the time foreign specialists landed in Kenya to help fight the outbreak, it had passed.

The response was much quicker last fall, thanks to the ability of public health agencies to predict the arrival of the virus. Health officials flew to Kenya in December within days of the confirmed arrival of the virus, and the death toll has been limited to 104 persons.

“Looking at the weather forecasting and satellite imaging data in November, we were already thinking, ‘Rift,’” said Dr. Pierre Formenty of WHO, recently in Kenya to help contain the outbreak.

Once Nairobi was informed of the likelihood of an outbreak, the Kenyan government outlawed the sacrificing of cows, camels, goats and sheep during the Muslim festival of Eid. The ban was imposed to minimize contact between humans and infected animals, and may have cut the risk factor for virus transmission to humans.

Rift Valley fever is not the only disease affected by weather. Any disease spread by insects such as malaria, yellow fever or encephalitis is dependent on the conditions needed for the insects’ survival, such as warm temperatures and plenty of water to breed.

Waterborne diseases such as cholera and typhoid are also particularly susceptible to weather changes.

Despite the established links between weather variability and disease outbreaks, global surveillance systems do not systematically monitor the weather.

“Some of my colleagues just laugh and tell me to open the window if I want to watch the weather,” Dr. Formenty said.

One problem is that disease response systems are already so stretched in developing countries that adding weather to the list of things to watch won’t necessarily help.

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