The outbreak predictor

Scientist uses weather data to calculate disease risk

February 09, 2007|By Dennis O'Brien | Dennis O'Brien,Sun reporter

Forecasts of snow may send people running to supermarkets for bread and toilet paper. But some scientists want their predictions to provoke a different reaction -- spurring health officials to prevent disease outbreaks and save lives.

Assaf Anyamba, a research scientist at the University of Maryland, Baltimore County and the Goddard Earth Sciences and Technology Center, warned officials in Kenya last fall that weather conditions were ripe for an outbreak of Rift Valley Fever, or RVF, a lethal disease transmitted by mosquitoes.

While the outbreak has not been contained, reports indicate that Anyamba's early warning may have saved lives.

Anyamba, born and raised in Kenya, has spent 10 years at Goddard's Greenbelt facilities using satellites to study how weather patterns spawn flooding, droughts and changes in vegetation that give rise to diseases.

Some analysts monitor RVF outbreaks out of concern over the germ's possible use as a bioweapon, experts say. But Anyamba focuses on outbreaks linked to El Nino, the periodic warming of surface waters in the Pacific Ocean that affects weather around the world.

As El Nino warms the surface of the central and eastern tropical Pacific, it affects atmospheric circulation, making some arid areas wetter and wet areas drier. Along the East Coast of the United States, scientists say, El Nino generally causes milder winters as it dumps increased rainfall along the Gulf of Mexico. But in other areas, it creates breeding grounds for deadly, disease-carrying mosquitoes.

In Africa, El Nino's consequences can be devastating. In the late 1990s, El Nino dumped unprecedented rainfall in the Sahel region of Africa, a strip of territory that separates the Sahara in the north from the Sudan to the south. The storms flooded dry areas and caused an outbreak of RVF that killed 400 people.

"Northeastern Kenya is normally a dry area, but when you change the circulation mechanism, you bring in all this moisture," Anyamba said.

Satellite data on sea surface temperatures, cloud patterns, rainfall totals and the grassy vegetation that make up the mosquito's habitat help Anyamba determine the threat of an RVF outbreak. In general, he can provide about three months' notice of an outbreak.

Last fall, when satellite data showed that an El Nino-related warming trend had produced prime conditions for another outbreak, he warned authorities by posting an alert on a United Nations Web site, briefing officials at a World Health Organization conference in Istanbul, Turkey, and sending word to colleagues assigned to a Department of Defense lab in Kenya.

Because the disease can be spread by eating infected cattle, the Kenyan government outlawed the sacrificing of cows, camels, goats and sheep during the Muslim festival of Eid, a celebration to end Ramadan, a month of fasting. Aid workers also distributed bed netting and bolstered supplies of drugs believed to help.

The death toll is at 140, according to news reports. But the government's response may save hundreds of lives, said Anyamba, who met with officials in Kenya in December during a follow-up visit.

"I think the government listened and responded pretty well," he said.

Researchers say linking weather patterns to disease outbreaks is a relatively new science. The warning issued in Africa last fall was among the first to draw such a decisive government response, they say.

"It took critical mass for us to establish our reputability and to get things rolling," said Kenneth J. Linthicum, director of the U.S. Department of Agriculture's Center for Medical Agricultural and Veterinary Entomology in Gainesville, Fla.

Responses to past warnings have been limited by a lack of resources in developing countries, they say.

"A lot of these countries are really stretched in terms of resources, so there is only so much they can do. But I think the importance of this kind of work is catching on," said Dr. Paul Epstein, associate director of the Harvard Medical School's Center for Health and the Global Environment.

RVF is not the only disease linked to weather. In the Southwestern United States, excessive rain produces grasses and shrubs that favor the hantavirus, a respiratory ailment spread by mouse excrement, said Greg Glass, a disease ecologist at the Johns Hopkins Bloomberg School of Public Health.

Hanta infection rates rise when deer mice populations increase and the animals invade people's homes, Glass said. He uses satellite imagery to help health authorities in the Southwest keep track of rainfall and vegetation patterns.

"It's a really unpredictable disease if you have it -- chances are 50-50 you could be dead in 24 to 48 hours," Glass said.

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