As human cases continue to climb in the latest outbreak of the deadly Ebola virus in the Democratic Republic of the Congo, concern is growing for the gorilla population, which have been devastated by the virus during previous outbreaks.
On May 15, the Congolese Health Ministry announced a new outbreak of the lethal virus, which has struck the country at least 17 times over the past half-century; the World Health Organization (WHO) declared it a Public Health Emergency of International Concern.
The U.S. Centers for Disease Control and Prevention confirmed 676 Ebola cases in the eastern DRC and 136 deaths as of June 10 — and continue to rise. In neighboring Uganda, 19 cases and two deaths have been reported, with no new cases in the last days. So far, the outbreak seems to be largely contained within the region.
The Bundibugyo virus is the culprit, one of five Ebola viruses within the family Filoviridae that spark illness in people. It has no approved treatment or vaccine.
As cases mount, virologists — as well as ecologists and primatologists — are warily monitoring its spread. First discovered in humans in 1976 along the Ebola River (where it got its name), Ebola is highly contagious, and this virus can also sicken and kill gorillas and other non-human primates. While some symptoms are flu-like — fever, vomiting and diarrhea — the disease can progress to a gruesome, often-fatal hemorrhagic fever, causing both internal and external bleeding.
Previous outbreaks have exacted vast human death tolls — but they’ve also decimated non-human primate populations in Central Africa. Researchers have called Ebola “a threat to the survival of African great apes.”
While there is currently no overlap between areas with reported cases and gorilla habitat in Uganda and DRC, the situation is evolving rapidly.
If it was to spread into areas populated by any of the four critically endangered gorilla subspecies, the consequences could be catastrophic.
Ebola is zoonotic, a type of disease that’s capable of jumping between livestock, wildlife and humans. Ebola is transmitted through direct contact with infected blood or body fluids — and by eating infected animals: bushmeat. Researchers have called the hunt for the virus’s natural host to be “an enduring mystery.” Testing from 1979-2025 found Ebola infection in 61 mammal species out of some 360 that were tested.
Western lowland gorillas (Gorilla gorilla gorilla) in the Republic of Congo have suffered massive losses during back-to-back human outbreaks, one near the Lossi Gorilla Sanctuary in 2002–2003 and another in Odzala-Kokoua National Park in 2004. With mortality rates from 90-95%, about 5,000 western lowland gorillas died in Lossi, a 5,000 square kilometer (1,930 square mile) study area, according to a report in the journal Science.
In concert with habitat loss and illegal hunting, the IUCN, the global wildlife conservation authority, changed its conservation status to critically endangered in 2007, one step from extinction. As of the last IUCN assessment, published in 2018, about 316,000 remained, with 60% in the Republic of Congo.
The other three subspecies seem to have been unaffected thus far. “As far as we know, all past Ebola outbreaks that have affected gorillas concerned the western lowland gorilla,” said Damien Caillaud, a behavioral ecologist at the University of California, Davis, in the U.S.
Gorillas are at great risk from infectious disease, because they’re social animals. They typically live in groups of eight to 10, typically a single adult male, several adult females and their offspring. Some adult males are solitary, waiting to find or form a group.
Caillaud witnessed firsthand the devastation of the early 2000s Ebola outbreak. He co-authored a paper on how gorilla sociability and group dynamics affect exposure.
“During these outbreaks,” he said, “we observed that Ebola spreads rapidly within gorilla groups, likely due to the physical contacts gorillas have during nap time, play or grooming sessions.” They found that solitary males are much less susceptible, but female gorillas are disproportionately affected, which makes it difficult for the population to recover.
When one animal is affected, transmission is fast. “Almost all the gorillas from the group disappear within a few weeks,” he said.
The researchers in Lossi observed the same level of mortality. They reported that “from October 2002 to January 2003, 91% (130/143) of the individually known gorillas in our study groups had disappeared.”
Gorillas stay near the dead body of a recently deceased individual, regardless of whether it belonged to their social group, according to a report in the journal Zoological Science. The researchers observed that healthy gorillas “will likely touch the body of a gorilla they randomly bump into in the forest,” Caillaud said.
Infant “corpse-carrying” behavior has also been observed in gorillas, where a mother carries an infant’s body for days — or even weeks — after its death, Tierra Smiley Evans, chief veterinary and scientific officer with the NGO Gorilla Doctors wrote in an email to Mongabay.
When gorillas die from Ebola, their dead bodies remain infectious for several days. It’s why carcasses “likely constitute one of the main sources of infection for unaffected gorilla groups ranging nearby,” Caillaud said. This could be one of the main pathways of infection that killed thousands of individuals in the early 2000s, he added.
