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  EurekAlert 10 Jul 06
Gorilla susceptibility to Ebola virus: the cost of sociality
Current Biology

Planet Ark 11 Jul 06
Socializing Helped Ebola Wipe Out Gorillas - Study
Story by Maggie Fox, Health and Science Correspondent

WASHINGTON - Social contact helped the Ebola virus virtually wipe out a population of gorillas in the Democratic Republic of Congo, French researchers reported on Monday.

A 2004 outbreak of the virus, which also kills people, killed 97 percent of gorillas who lived in groups and 77 percent of solitary males, Damien Caillaud and colleagues from the University of Montpellier and the University of Rennes in France reported. Overall, it wiped out 95 percent of the gorilla population within a year, they reported in the journal Current Biology.

"Thousands of gorillas have probably disappeared," they wrote. The study shows that the deadly virus spreads directly from gorilla to gorilla and does not necessarily depend on a still-unidentified third species of animal, perhaps a bat, that can transmit the virus without getting ill from it.

It also may shed light on how early humans evolved, they suggested. The findings may show that pre-humans were slow to live in large social groups because disease outbreaks could wipe out those who did.

Ebola hemorrhagic fever is one of the most virulent viruses ever seen, killing between 50 percent and 90 percent of victims. The World Health Organization says about 1,850 people have been infected and 1,200 have died since the Ebola virus was discovered in 1976.

WHO and other experts say people probably start outbreaks when they hunt and butcher chimpanzees. The virus is transmitted in blood, tissue and other fluids.

Caillaud's team said Ebola is a serious threat to the survival of endangered gorillas and chimpanzees, along with hunting and the destruction of the forests they live in.

The researchers documented one outbreak of Ebola and its effects on gorillas and people in Odzala-Kokoua National Park.

"On October 13, 2003, two villagers from Mbandza hunting at an undetermined site inside the park got contaminated and became index cases of an outbreak that killed 29 people in seven weeks," they wrote. They were able to identify 400 individual gorillas.

"Overall, 109 distinct gorilla social units visiting Lokoue were reliably identified and monitored during a 1,360-day period." By July 2004, nearly all the gorillas were dead.

"Due to intra-group transmission, the death rate was highest among gorillas living in groups," the researchers wrote.

Health workers move in fast when Ebola breaks out among humans, to isolate patients and to make sure everyone who has contact with them wears protective clothing.

EurekAlert 10 Jul 06
Gorilla susceptibility to Ebola virus: the cost of sociality
Current Biology

By monitoring a large population of gorillas during an Ebola outbreak in the rain forest of the Republic of the Congo, researchers have found that in a few months the virus exhibited dramatic--but disproportionate--impacts on group-dwelling and solitary gorillas.

The findings offer a unique glimpse into the factors affecting the threat the deadly virus poses to great apes. The work is reported in the July 12th issue of the journal Current Biology by a team of researchers including Damien Caillaud and colleagues from the University of Montpellier and the University of Rennes, France.

Ebola virus is extremely lethal for humans and other great apes. Since 1994, the Zaïre subtype of the Ebola filovirus has been responsible for nine human outbreaks in Gabon and the Republic of the Congo; a majority of these outbreaks have originated from the handling of infected great-ape carcasses.

In fact, Ebola virus has become one of the major threats to the survival of western lowland gorillas (Gorilla gorilla gorilla) and chimpanzees (Pan troglodytes troglodytes) in this region.

However, the causes of outbreak among wild animals, and the way the virus spreads, remain unclear. It has been argued that the infection of apes only occurs by way of the so-called "reservoir" species (unknown, but possibly fruit bats), with ape-to-ape transmission playing only a minor role due to an insufficient rate of encounters between groups.

In the new work, the researchers studied the spread of Ebola virus in a gorilla population of Odzala-Kokoua National Park, Republic of the Congo. Social units--defined as groups and solitary males--composing this population regularly visited a forest clearing where they were studied from 2001.

In all, around 400 gorillas were identified from their individual morphological characteristics. Ebola virus affected this population in 2004. During and after the outbreak, the researchers used the data on the identity of animals previously observed to estimate Ebola-induced mortality and to test the validity of different possible contamination scenarios.

The authors of the study showed that transmission between gorillas was particularly important within groups and led to a very high mortality rate--97% of group-dwelling individuals.

In contrast to the hypothesis expressed above, evidence suggested that transmission between social units is also likely to occur, either exclusively or in addition to reservoir-to-gorilla transmission, and the result was a mortality rate of 77% of solitary males.

Overall, 95% of the population disappeared in approximately one year.

From a conservation point of view, this finding is worrying because all adult female and young gorillas--on whom post-epidemic population recovery relies--live in groups.

These findings provide new insights into what is still a poorly understood disease and could shed light on the evolutionary costs experienced by primates living in groups.

The authors note that thousands of gorillas have probably disappeared as a result of the Ebola outbreak studied here, and they point out that because the impact of Ebola on apes is still difficult to control, strengthened protection of gorillas and chimpanzees is needed throughout their range, especially against the other primary threats to their survival: poaching and logging.
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