Does ivermectin treatment for endemic hookworm infection alter the gut microbiota of endangered Australian sea lion pups?

The gut microbiota is essential for the development and maintenance of the hosts immune system, and disturbances can impact host health. This study aimed to determine if topical ivermectin treatment for endemic hookworm (Uncinaria sanguinis) infection in Australian sea lion (Neophoca cinerea) pups causes gut microbial changes. The gut microbiota was characterised for untreated (control) (n=23) and treated (n=23) pups sampled during the 2019 and 2020/21 breeding seasons at Seal Bay, Kangaroo Island. Samples were collected pre- and post-treatment on up to four occasions. The gut microbiota of both untreated (control) and treated pups was dominated by five bacterial phyla, Fusobacteria, Firmicutes, Proteobacteria, Actinobacteria and Bacteroides. There was a significant difference in alpha diversity between treatment groups in 2020/21 (p = 0.008), with greater diversity in treated pups. Modelling the impact of host factors on beta diversity revealed that pup ID accounted for most of the variation with pup ID, age and capture being the only significant contributors to microbial variation (p < 0.05). There were no statistically significant differences in microbial composition between treatment groups in both breeding seasons, indicating that ivermectin treatment did not alter microbial composition. To our knowledge, this is the first study to consider the impact of parasitic treatment on overall diversity and composition of the gut microbiota. Importantly, the lack of compositional changes in the gut microbiota with topical treatment support the utility of topical ivermectin as a safe and minimally invasive management strategy to enhance pup survival in this endangered species. ImportanceDisturbances to the gut microbiota in early life stages can have life-long impacts on host health. Australian sea lions are endangered and declining, and pups are endemically infected with hookworm (Uncinaria sanguinis) which contributes to pup mortality. Treatment with topical ivermectin has been shown to effectively eliminate hookworm infection and to improve pup health, but the impact on the gut microbiota was previously unknown, representing a key knowledge gap. The results from this study show that topical ivermectin treatment does not alter the gut microbiota of Australian sea lion pups, indicating that it is a safe and minimally invasive treatment that can aid in disease mitigation and conservation of this endangered species.