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.