Updated: Mar 20, 2020
The Eastern Gorilla (Gorilla beringei) is native to forest habitats, including swamps, moist lowland, and mountains in the Democratic Republic of Congo (DRC), Rwanda, and Uganda. As per the most recent iteration of the IUCN Red List, the Eastern Gorilla is critically endangered, with an estimated wild population of less than 5,000 individuals, having decreased by 77% between 1995 and 2015.
A number of factors are contributing to the decline of gorilla populations. Habitat destruction and climate change are among the most prevalent, though they are also caught up in the bushmeat trade at times. Conservation activities are ongoing where possible, educating local populations and lobbying against deforestation. There is something else that is endangering gorilla populations, something conservation work has seldom addressed to date – infections with Ebolavirus Disease (EVD).
The Ebola virus, which causes EVD, is a member of the filoviridae family of viruses. Six virus species have been identified within the ebolavirus genus of filoviridae. Four of these – Zaire, Sudan, Bundibugyo, and Taï Forest – cause disease in humans and non-human primates. The Reston subtype is known to only infect non-human primates. Bombali, the sixth subtype, was recently discovered in fruit bats but has not yet been shown to cause disease in humans or any other species.
It has long been suspected that bats or other small mammals are carriers of the virus and that consuming infected flesh or coming into contact with infected faeces or bodily fluids is the main mode of transmission. Ebolavirus Bombali – having now been identified in bats – seems to corroborate that hypothesis, though until one of the disease-causing species is identified in a bat or small mammal, it cannot be definitively proven.
Many of us became familiar with EVD in 2014, when a particularly virulent strain ripped through towns and cities in Liberia, Guinea, and Sierra Leone. According to the World Health Organisation, there were over 28,000 human infections and 11,300 deaths from EVD between 2014 and 2016. That doesn’t include the deaths from other diseases, such as malaria, that were neglected due to the breakdown of health services during that time. There is an ongoing outbreak in the DRC which began in August 2018 – 3,300 infections have been confirmed with 2,200 deaths. Both outbreaks were caused by the Zaire subtype.
The mortality rate of EVD in humans now stands at around 50% thanks to improvements in supportive care, quarantine behaviours, and education of medical professionals and local communities. The current outbreak in the DRC has provided the necessary scientific drive to create a vaccine to protect people in the affected areas. A vaccine developed by Merck has proven 97% effective in humans and a second vaccine developed by Johnson and Johnson has just been approved for use in the DRC by the WHO and local authorities. Ring-vaccination, the method that was used to eliminate smallpox from humans and to control polio in all but a few countries, is being used to try and stem this EVD outbreak.
Gorillas are not as fortunate when it comes to EVD outbreaks in their populations. Up to a third of Western Lowland Gorillas were wiped out by EVD infections in the early 2000s. As gorillas in the wild are spread out over large habitats and can be difficult to track, estimating the impact of an outbreak on the population has many challenges. One thing that is for sure, is that once EVD is in a gorilla population it becomes very difficult to control. Without the benefit of supportive care and quarantine, the mortality rate is closer to 90%.
Gorilla conservation workers are actively monitoring the critically endangered Eastern Gorilla populations across the DRC and Uganda, where the current Ebola outbreak is active. Many of these gorilla populations are used to humans, due to extensive conservation work and wildlife tourism in the national parks where they live. This puts them at greater risk of contracting EVD by coming into contact with an infected human, much higher than if they only risked contracting it from their natural surroundings.
The Eastern Gorilla, with fewer than 5,000 individuals, could be wiped out by an uncontrolled EVD outbreak. Dr Peter Walsh, a primate ecologist, is an advocate of vaccinating gorilla populations as early as possible. According to National Geographic, vaccination could be possible in these populations due to their comfort with humans. While this puts them at greater risk of infection, it could also allow vets to get close enough to individuals to dart them with vaccine, protecting them from EVD.
Time is running short. Once EVD is in a gorilla population, it will be too late to vaccinate, and we could be looking at the functional extinction of an important primate species. Historically, there has been objections from conservationists to vaccinating wild animals, as they argue it interferes with the natural order of things. Furthermore, testing on captive non-human primates has been all but eliminated from medical research, and untested vaccines with unforeseen side effects could never be used on a wild population.
As sporadic and virulent EVD outbreaks continue to crop up across Africa, the risk to humans and their non-human brethren will persist. The difference is we’re addressing the human risk and ignoring the other. Vaccine testing on primates for primates may need to become a part of conservation activities in order to save these species into the future.