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. Disturbances to the gut microbiota in early life
stages can result in long-lasting impacts on host health. This study aimed
to determine if topical ivermectin treatment for endemic hookworm
(Uncinaria sanguinis) infection in endangered Australian sea lion
(Neophoca cinerea) pups resulted in gut microbial changes. The gut
microbiota was characterised for untreated (control) (n = 23) and treated
(n = 23) Australian sea lion 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 over a four-to-five-month
period. The gut microbiota of untreated (control) and treated pups in both
seasons were dominated by five bacterial phyla, Fusobacteria, Firmicutes,
Proteobacteria, Actinobacteria, and Bacteroides. A significant difference
in alpha diversity between treatment groups was seen in pups sampled
during the 2020/21 breeding season (p = 0.008), with higher richness and
diversity in treated pups. Modeling the impact of individual pup
identification (ID), capture, pup weight (kg), standard length (cm), age,
and sex on beta diversity revealed that pup ID accounted for most of the
variation (35% in 2019 and 42% in 2020/21), with pup ID, capture, and age
being the only significant contributors to microbial variation (p <
0.05). There were no statistically significant differences in the
composition of the microbiota between treatment groups in both the 2019
and 2020/21 breeding seasons, indicating that topical ivermectin treatment
did not alter the composition of the gut microbiota. To our knowledge,
this is the first study to characterise the gut microbiota of free-ranging
Australian pinniped pups, compare the composition across multiple time
points, and consider the impact of parasitic treatment on the overall
diversity and microbial composition of the gut microbiota. Importantly,
the lack of compositional changes in the gut microbiota with topical
ivermectin treatment supports the utility of topical ivermectin as a safe
and minimally invasive management strategy to enhance pup survival in this
endangered species.