The Ebola virus has killed some 1,300 people in Central Africa over the last 30 years. In most of these cases where it has been possible to trace the source of the outbreak, it has been associated with the consumption of contaminated apes or antelopes. But very little has been known about contagion in natural populations.
In the present study an international research team, including a group from Uppsala University in Sweden, has tracked two outbreaks and followed their spread among a gorilla population in Lossi Reservation in the Republic of Congo. The gorilla populations have been monitored by some of the scientists since 1995. As a result of this, 17 gorilla groups with a total of 238 individuals have grown accustomed to the presence of humans. However, two outbreaks of Ebola virus, one between October 2002 and January 2003 and the other between October 2003 and January 2004, led to the death of 221 of them (93%). To examine whether this high mortality rate also affected the area outside the reservation, the researchers carried out a study of a larger area (2,700km2) and found that 96 percent of the gorillas had disappeared. A total of 5,000 gorillas are estimated to have died from Ebola.
“These figures unfortunately represent merely a portion of the area that the virus has infected, and gorillas are continuing to die in this region,” says Carles Vilà.
Careful monitoring has revealed that the transmission between gorilla groups has probably played a key role in the spread of the disease. This also means that the researchers reject the possibility that the outbreaks were the result of a massive transmission of the virus from a reservoir (e.g. mosquitoes or bats). An important conclusion of the study is therefore that vaccinating the as yet unaffected gorillas may be a key measure to stop the spread of Ebola among gorillas.
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