Ebola Virus Plus Hunting Could Wipe Out Gorillas

WASHINGTON, DC, December 7, 2006 (ENS) - 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.

In today's issue of the journal "Science" researchers from Spain and Germany present evidence that over the past four years so many gorillas have died from the highly contagious disease that the species could become extinct if hunters continue to prey upon them as well.

"The Zaire strain of Ebola virus killed about 5,000 gorillas in our study area alone," writes the research team, headed by primatologist Magdalena Bermejo of the University of Barcelona in Spain and the Ecoystemes Forestiers d'Afrique Centrale, based in Gabon.

"Add commercial hunting to the mix, and we have a recipe for rapid ecological extinction," the scientists write. "Ape species that were abundant and widely distributed a decade ago are rapidly being reduced to tiny remnant populations."

Lowland gorilla in the Lossi Sanctuary, created in 2001 to attract tourists interested in viewing wildlife. (Photo by Norbert Gami courtesy FAO)

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.

Based on that finding, the scientists estimate about 5,000 gorillas living in the region have died from Ebola virus infection since the epidemic began in 2002.

The Zaire strain, one of four viral subtypes, has infected humans in Gabon and Congo, said 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.

Local villagers carry bark into the Lossi Sanctuary to build huts for tourists. (Photo by Norbert Gami courtesy FAO)

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.

Results of the Lossi Sanctuary study are consistent with a study published in the January 2007 issue of the journal "Transactions of the Royal Society of Tropical Medicine and Hygiene," which demonstrates that Ebola virus transmission among animals is more pervasive than scientists previously thought.

Sally Lahm, a scientist at the Institute for Research in Tropical Ecology in Makokou, Gabon, tracked animal disease outbreaks and human exposure to the Ebola virus in Gabon and the northwestern Congo Republic from 1994 to 2003.

Lahm and her colleagues collected reports of animal illness and deaths from wildlife survey teams, villagers, hunters, fishers, loggers, miners, Ebola survivors and families of victims.

"The transmission of Ebola within animal populations is much more widespread than previously believed," said Lahm in November. "Ebola appears to spread both within species and between different species of animals."

Based on human blood samples that tested positive for antibodies to Ebola and interviews with the antibody-positive people, Lahm tracked the spread of the Ebola virus. Her study proposes that the disease first spread southwest across Gabon and then looped back toward the northeast from sites in western or central Gabon and caused the most recent outbreaks in Republic of Congo.

"If the spread of the Ebola virus follows its current northeastward path, the next outbreak would be expected to occur in northern Republic of the Congo towards Cameroon and the Central African Republic," predicted Lahm.

According to Lahm's findings, the spread of Ebola also depends on climate factors. Illness and deaths among animals were most prevalent during periods of prolonged drought-like conditions in the rainforest, which indicates that severe environmental stress may facilitate disease transmission.