Shifts in strongylid communities associated with chronic wasting in mountain gorillas.

Host-parasite relationships are typically maintained in a dynamic equilibrium, but disruptions to this balance can lead to clinical disease and population-level health impacts. Chronic wasting, characterized by chronic loss of body condition, alopecia, a browning hair coat and pot belly, is an emerging health concern in mountain gorillas of Bwindi Impenetrable National Park, Uganda. Deworming of suspected cases has led to marked short-term health improvements, implicating intestinal helminths. To investigate, we analysed faecal samples from human-habituated gorillas collected in 2018 and 2021, and unhabituated gorillas in 2018, using high-throughput sequencing of strongylid nematodes (ITS-2) and gut bacteria (16S). Strongylid community composition varied with chronic wasting occurrence, with Oesophagostomum emerging as a key taxon driving this difference, while bacterial communities remained relatively stable. Strongylid diversity increased between 2018 and 2021, and habituated gorillas exhibited reduced strongylid genetic diversity, higher relative abundance of Oesophagostomum and lower relative abundance of Murshidia compared to unhabituated gorillas. These results suggest that a higher abundance of Oesophagostomum is associated with chronic wasting in mountain gorillas due to either a causative association or other genetic, immunological or environmental causes allowing Oesophagostomum, a common member of the gut eukaryote community of the Bwindi gorillas, to overpopulate.