5th of February 2026, Brno
Mountain gorillas, a well-known symbol of successful nature conservation, have recently been affected by a serious health problem. An international team of scientists has found that severe cases of gastritis, including fatalities, are linked to changes in parasite communities—specifically a marked increase in nematodes of the genus Hyostrongylus, commonly found in domestic pigs. The results, published in the Journal of Applied Ecology, highlight the importance of long-term monitoring for the protection of this iconic species.
The conservation of mountain gorillas is one of the greatest successes in wildlife protection, having reversed a long-term population decline and achieved stable population growth in the wild. However, new research shows that population recovery also brings new health risks. Scientists found that severe cases of gastritis, sometimes leading to death, are associated with changes in parasite communities, particularly an increase in Hyostrongylus nematodes, commonly found in livestock.
The study, which analysed parasites in nearly two-thirds of the mountain gorilla population, was conducted in 2018 in the Virunga Mountains on the borders of Uganda, Rwanda, and the Democratic Republic of Congo. It combined classical parasitology, genetic sequencing, and spatial analyses.
“Our results show that disease occurrence is not evenly distributed. The highest number of severe gastritis cases occurs in high-altitude areas between Mounts Karisimbi and Bisoke, where Hyostrongylus nematodes reach the highest infection intensities,” explains Klára Petrželková from the Institute of Vertebrate Biology of the Czech Academy of Sciences.
“This is not about the discovery of entirely new parasites. The problem lies in changes in the composition and abundance of parasite communities that have long been present in the mountain gorilla population, with some species now becoming dominant and clinically significant. Similar processes are well known in livestock farming, where high host density, spatial restriction, and environmental changes often lead to the overgrowth of previously inconspicuous parasites and the development of disease,” explains Barbora Pafčo from the same institute.
A comparable mechanism is now observed in mountain gorillas, but in a conservation context. Historically, Virunga gorillas, especially on the Rwandan side of the mountains, were pushed from lower elevations to higher altitudes due to habitat loss associated with agricultural expansion. These higher areas are characterized by cooler, wetter conditions. According to research, temperature and precipitation strongly influence the composition of parasite communities. Combined with the very low genetic diversity of mountain gorillas, resulting from a historical population bottleneck (a drastic population decline from which future generations arise from only a few survivors), these factors may increase susceptibility to parasite-driven diseases.
The researchers also highlight the potential role of livestock. Hyostrongylus nematodes are typical parasites of pigs, and pigs are commonly kept near national park boundaries. Fields surrounding the parks are often fertilized with manure, which may serve as a source of parasite infection near gorilla habitats. Gorillas also occasionally enter agricultural land, creating opportunities for indirect parasite transmission between wild and domestic species.
Recommendations for gorilla conservation
The authors warn that the successful recovery of mountain gorilla populations brings new challenges that were not relevant in the recent past. Increasing population size in a spatially limited and environmentally heterogeneous landscape can affect the dynamics of infectious diseases, including parasitic infections.
The study therefore emphasizes the importance of long-term, systematic health monitoring of gorillas. Effective monitoring combines modern pathogen diagnostics with routine health surveillance of habituated gorillas, carried out in the Virunga region by field veterinarians from the Gorilla Doctors, who initiated and participated in the study. Special attention should also be given to livestock pathogens around national parks, which may serve as reservoirs for parasites shared with wildlife.
“The conservation of mountain gorillas is one of the most successful examples of endangered species protection, yet it also shows that in small, spatially restricted populations, new ecological conditions can lead to health problems,” says Klára Petrželková.
“Our results highlight that parasites common in livestock can, under certain conditions, pose a risk to wild populations, particularly in areas strongly influenced by human activity. Similar mechanisms therefore do not concern gorillas alone but may also threaten other small, isolated populations of protected species,” adds Barbora Pafčo.
Publication: https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2664.70258
