Endangered mountain gorillas hold their own against deadly Ebola

If infected with Ebola virus, less than 20 percent of endangered mountain gorillas living in Africa’s Virunga Massif region that straddles the Democratic Republic of the Congo (DRC), Rwanda, and Uganda would survive more than 100 days past the first confirmed case.

This is according to a new study in Scientific Reports simulating and projecting the impacts an Ebola virus outbreak would have among mountain gorilla populations living in the three countries. The Ebola virus is highly lethal for great apes. Estimated mortality rates up to 98 percent have reduced the global gorilla population by approximately one-third. There are just over 1,000 individuals remaining in the world.

While there have been no confirmed cases of Ebola virus in wild great apes since 2005, Ebola is present and circulating in East-Central Africa. Findings indicate that estimated contact rates among gorilla groups in the region are high enough to allow rapid spread of Ebola.

Cross-species transmission

Yet, scientists think there is cause for concern for cross-species transmission where intense human-wildlife overlap. Great apes, human’s closest relatives, share susceptibility to many of the same illness-causing pathogens in humans.

Read: Ebola vaccine trials show great promise

The increasing threat of disease transmission among wildlife, domestic animals, and humans is predicated on the growth of human populations and subsequent land-use change, driving opportunities for disease spill over. An estimated 72 percent of emerging infectious diseases (EIDs) originate in wildlife.

The scientists are calling for proactive measures at the human-wildlife interface for the mitigation of EIDs and drivers leading to an increased risk of disease transmission from humans to wildlife and vice versa.

A health worker disinfecting someone’s shoes in Mubende, Uganda on October 27, 2022 following the Ebola outbreak. PHOTO | BADRU KATUMBA | AFP

While none of the vaccine strategies examined will prevent widespread infection, the study projects survival rates of 50 percent or greater being achieved by vaccinating at least half of the habituated gorillas within three weeks of confirming the first infected gorilla.

Outbreak software

The study published April 7, titled Projecting the Impact of an Ebola Virus Outbreak On Endangered Mountain Gorillas, was conducted by researchers affiliated with the Smithsonian Institution, as well as scientists from Gorilla Doctors (University of California) that work with the gorilla populations in the region, Davis-the Species Conservation Toolkit Initiative, Virginia Tech and other institutions, using computational modelling.

The study used Outbreak software, an open-source tool that allows conservationists to predict impacts of disease in populations or ecosystems. The scientists examined the potential population impact if a single individual gorilla were to be infected with Ebola virus.

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“We have been very lucky that to date, Ebola virus has not impacted mountain gorillas,” said senior author and Gorilla Doctors Executive Director Kirsten Gilardi, and also professor with the Karen C. Drayer Wildlife Health Centre at UC Davis’ School of Veterinary Medicine.

 “The findings provide further support for vigilant pathogen surveillance and contingency planning to mitigate the risk of Ebola virus entering the mountain gorilla population. That we were able to produce these findings with data provided from Rwandan, Ugandan, and DRC wildlife authorities demonstrates their commitment to protecting these magnificent great apes.”

Tight-knit grouping

Mountain gorillas are social animals living in tight-knit groups that sometimes come into contact with other groups.

“The Virunga Massif mountain gorilla population is isolated in national parks – forest ‘islands’ surrounded by some of the highest human population densities in Africa – and we know that gorillas are susceptible to human pathogens,” said lead author Dawn Zimmerman, research associate with the Smithsonian National Museum of Natural History.

“The risk of spill over from humans to gorillas is significant. This study makes a strong case for either pre-emptively vaccinating 50 percent of the habituated mountain gorillas or being ready to vaccinate at the first detection of Ebola in the population. While it won’t prevent widespread infection, it could increase the survival rate across the population to as much as 50 percent.”

Land use patterns

“As human population growth and changing land use patterns continue to increase the pressures on and threats to wildlife, predictive models such as this one can help strengthen existing strategies and cooperation to protect wildlife from devastating disease outbreaks,” Senior author Robert Lacy with the Species Conservation Toolkit Initiative said.

The paper highlighted the critical importance of preparedness and continued monitoring and surveillance of wildlife populations for the detection of infectious disease.

Ebola virus — considered endemic in East-Central and West Africa, with concern for cross-species transmission in regions of intense human-wildlife overlap, has caused significant mortality in both humans and great apes, estimated to have reduced the global gorilla population by approximately one-third with social impacts on gorillas likely persisting for years, population recovery predicted to take decades and genetic impacts potentially persisting for centuries.