The Ebola virus has wiped out as many as 5,000 lowland gorillas in the region surrounding the Lossi Sanctuary in Africa, a much higher number than previous estimates, according to new research published today. The scientists propose that ape-to-ape transmission is a major factor in the spread of the disease among the endangered animals.

This Ebola outbreak is not the first to devastate gorillas in and around the Lossi Sanctuary in the northwestern Republic of Congo near the Gabon border. The Republic of Congo is the country to the west of the larger nation of Congo, formerly known as Zaire.

Beginning in August 2002 and continuing in 2003, about half of the previously estimated population of 1,200 gorillas living in and around the sanctuary were found to have died from Ebola infection. A survey of nesting sites used by gorillas in a 2,000 square mile area around the sanctuary found that the number of occupied nests had fallen by 96 percent .

The Zaire strain, one of four viral subtypes, has infected humans in Gabon and Congo, said primatologist Magdalena Bermejo, who has been studying the gorillas of the Lossi Sanctuary since 1994.

The researchers estimate that one-fourth of the world's gorillas have died from the disease since then, but they stress that no one knows precisely how many gorillas still exist and how many have died of Ebola infection.

Each time there is a human outbreak, carcasses of gorillas and chimpanzees have been found in nearby forests. One of the most deadly viruses known, Ebola hemorrhagic fever causes death in 50 to 90 percent of all clinically ill cases, according to the World Health Organization, WHO. Since the disease was discovered in 1976, it has caused over 1,200 human deaths.
WHO says the virus is transmitted among people by direct contact with the blood, secretions, organs or other bodily fluids.

Dr. Bermejo and her colleagues indicate in their paper that the virus appears to be spreading from one gorilla group to another in a manner consistent with ape-to-ape transmission. But exactly how gorillas pick up the infection is still unknown.

Scientists speculate that the natural reservoir is fruit eating bats that also inhabit the dense Congolese rainforests. Laboratory observation has shown that bats experimentally infected with Ebola do not die, and this has raised the possibility that these mammals may play a role in maintaining the virus in the tropical forest. Extensive ecological studies are underway in the Republic of Congo and Gabon to identify the Ebola's natural reservoir.