Ivermectin treatment of free-ranging endangered Australian sea lion (Neophoca cinerea) pups: effect on hookworm and lice infection status, haematological parameters, growth, and survival.

A placebo-controlled study was used to investigate the effectiveness of ivermectin to treat hookworm (Uncinaria sanguinis) and lice (Antarctophthirus microchir) infections in free-ranging Australian sea lion (Neophoca cinerea) pups and to test the hypotheses that these parasitic infections cause anaemia, systemic inflammatory responses, and reduced growth, and contribute towards decreased pup survival. Ivermectin was identified as an effective and safe anthelmintic in this species. Pups administered ivermectin had significantly higher erythrocyte counts and significantly lower eosinophil counts compared to controls at 1-2 months post-treatment, confirming that U. sanguinis and/or A. microchir are causatively associated with disease and demonstrating the positive effect of ivermectin treatment on clinical health parameters. Higher growth rates were not seen in ivermectin-treated pups and, unexpectedly, relatively older pups treated with ivermectin demonstrated significantly reduced growth rates when compared to matched saline-control pups. Differences in survival were not identified between treatment groups; however, this was attributed to the unexpectedly low mortality rate of recruited pups, likely due to the unintended recruitment bias towards pups >1-2 months of age for which mortality due to hookworm infection is less likely. This finding highlights the logistical and practical challenges associated with treating pups of this species shortly after birth at a remote colony. This study informs the assessment of the use of anthelmintics as a tool for the conservation management of free-ranging wildlife and outlines essential steps to further the development of strategies to ensure the effective conservation of the Australian sea lion and its parasitic fauna.