When Ebola looms: human outbreaks follow animal infections.

Before two recent human outbreaks of Ebola hemorrhagic fever in a region of Africa prone to epidemics of the disease, researchers identified the virus in wildanimal carcasses. Animal deaths could therefore signal a need for prevention efforts that would save people from dying, the researchers say.

For several decades, Ebola virus has caused sporadic African epidemics of fever and severe internal bleeding. There is no cure or proven vaccine, and most infected people die. Outbreaks begin when people handle infected meat or animals, particularly great apes, although it's not known how the animals contract the virus. Wild-animal meat is a major source of protein for people living in forests in the region.

To anticipate epidemics, scientists with the International Medical Research Center of Franceville (CIRMF) in Gabon teamed with several academic institutions, government ministries, and international conservation groups. From 2001 to 2003, the collaborating researchers recorded information about carcasses of certain wild species discovered in 20,000 square kilometers of forest that straddle Gabon and the Republic of Congo. The species included gorillas, chimpanzees, various monkeys, and antelopes known as duikers. In the February Emerging Infectious Diseases, the team reports on 98 animal deaths, most occurring in two waves.

Pierre Rouquet and other CIRMF veterinarians traveled to and tested 21 of the animals' remains for Ebola virus. The group wore protective suits while gathering and testing bone and also muscle and skin, if not yet decomposed. Ten gorillas, three chimpanzees, and one duiker were positive for Ebola. The researchers found evidence of the virus in both clusters of animal deaths.

Two Ebola outbreaks in the region arose in animals and spread to people after the monitoring network was in place. One human epidemic began in December 2002 and the other in November 2003. After identifying infected animals, the researchers warned local health authorities several weeks or months before people fell ill.

Monitoring animal deaths to warn people of imminent threats of Ebola is "a good way to go," says virologist Heinz Feldmann of the governmental department Health Canada in Winnipeg, Manitoba. While finding and testing carcasses requires extensive resources, the new report suggests that even without such sampling, a sudden, localized rise in deaths among great apes provides a strong indicator that Ebola is active, he says.

However, Feldmann notes that human outbreaks occurred despite the network's warnings.

For future discoveries of impending danger to lead to more-effective prevention measures, Rouquet says, scientists and health authorities need to develop greater trust and better communication with people living in the region.