Projecting the impact of an ebola virus outbreak on endangered mountain gorillas

Abstract

Ebola virus is highly lethal for great apes. Estimated mortality rates up to 98% have reduced the global gorilla population by approximately one-third. As mountain gorillas (Gorilla beringei beringei) are endangered, with just over 1000 individuals remaining in the world, an outbreak could decimate the population. Simulation modeling was used to evaluate the potential impact of an Ebola virus outbreak on the mountain gorilla population of the Virunga Massif. Findings indicate that estimated contact rates among gorilla groups are high enough to allow rapid spread of Ebola, with less than 20% of the population projected to survive at 100 days post-infection of just one gorilla. Despite increasing survival with vaccination, no modeled vaccination strategy prevented widespread infection. However, the model projected that survival rates greater than 50% could be achieved by vaccinating at least half the habituated gorillas within 3 weeks of the first infectious individual.

Figure 1

Timeline and locations of human Ebola virus outbreaks in the Democratic Republic of Congo (DR Congo). Outbreak data from: Centers for Disease Control and Prevention (2022). Map created with ArcGIS Online (Version 2.8), Esri Inc. https://www.esri.com/en-us/arcgis/products/arcgis-online/overview. *pooled from multiple outbreaks. **size of circle represents size of ebolavirus outbreak in local geographic area.

Figure 2

Locations of 2018–2021 human Ebola virus cases in the Democratic Republic of Congo (DRC) in proximity to the Virunga Massif and Bwindi mountain gorilla habitats. Outbreak data from: Centers for Disease Control and Prevention (2022). Map created with ArcGIS Online (Version 2.8), Esri Inc. https://www.esri.com/en-us/arcgis/products/arcgis-online/overview. *size of circle represents size of Ebola virus outbreak in local geographic area.

Figure 3

Proportions of SEIR states in the population and projected time course of Ebola virus transmission after entering the mountain gorilla population through one infected individual in the DRC-1 group at Day 0. S—Susceptible, never infected; E—Exposed and infected; I—Infectious; R—Recovered. Results averaged across 500 iterations.

Figure 4

Proportions of SEIR states in the population and projected time course of Ebola virus transmission after entering the mountain gorilla population with one infected individual in the DRC-1 group at Day 0, when vaccinations had been administered preemptively to 50% of the habituated gorillas. S—Susceptible, never infected; E—Exposed and infected; I—Infectious; R—Recovered; V—Effectively vaccinated. Lines averaged across 500 iterations.

Figure 5

Proportions of SEIR states in the population and projected time course of Ebola virus transmission after entering the mountain gorilla population with one infected individual in the DRC-1 group at Day 0, when vaccinations are administered to 50% of the habituated gorillas 6 weeks after the first gorilla becomes infectious. S—Susceptible, never infected; E—Exposed and infected; I—Infectious; R—Recovered; V—effectively Vaccinated. Lines averaged across 500 iterations.

Figure 6

Mean end counts (the number of surviving individuals at the end of the year) by disease state listed in order of least survival to greatest survival for the various vaccination scenarios. This demonstrates that the pathogen sweeps through the population in every scenario. PE—preemptive; vax—vaccination of habituated gorillas.