ORIGINAL PAPER Ivermectin treatment of free-ranging endangered Australian sea lion (Neophoca cinerea) pups: effect on hookworm and lice infection status, haematological parameters, growth, and survival Alan D. Marcus 1 & Damien P. Higgins 1 & Rachael Gray 1 Received: 27 March 2015 /Accepted: 9 April 2015 # Springer-Verlag Berlin Heidelberg 2015 Abstract 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 causa- tively 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 ivermec- tin demonstrated significantly reduced growth rates when compared to matched saline-control pups. Differences in sur- vival 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. Keywords Antarctophthirus microchir . Australian sea lion . Ivermectin . Neophoca cinerea . Uncinaria sanguinis . Wildlife disease Introduction Parasites profoundly impact the health and population dynam- ics of many free-ranging species (Smith et al. 2009; Thompson et al. 2010). Parasitic infection may be associated with clinical or subclinical disease, which can be evident by alterations in haematological values, changes in behaviour, and/or reduced growth rates, and can contribute directly or indirectly towards mortality (Irvine 2006; Bordes and Morand 2011). Conversely, parasites may confer an advantage to their host by stimulating development of the immune sys- tem or delaying physiologically expensive activities such as reproduction (Van Oers et al. 2002; Telfer et al. 2005). However, as ill-health can itself exacerbate parasitism, exper- imental manipulation of the host-parasite relationship is re- quired to verify causal relationships and quantify the impact of parasitic infection, both of which are necessary to inform conservation management on the effectiveness of and need for control strategies (Irvine 2006; Stringer and Linklater 2014). The Australian sea lion (Neophoca cinerea) is an endan- gered (IUCN Red List of Threatened Species; Goldsworthy and Gales 2008) and vulnerable (EPBC Act 1999) pinniped species endemic to Australia. These threatened species listings are based on the Australian sea lion’ s small, genetically fragmented population, population declines at some colonies, and the risk of extinction from fishery by-catch. Population recovery could be limited by their extended breeding cycle * Rachael Gray rachael.gray@sydney.edu.au 1 Faculty of Veterinary Science, The University of Sydney, McMaster Bldg B14, Sydney, New South Wales 2006, Australia Parasitol Res DOI 10.1007/s00436-015-4481-4