This study has shown that the NZ sub-Antarctic islands remain relatively pristine with respect to pathogens known to be commonly present on the mainland. On the other hand, reproductive success, particularly early pup survival at this location is under the influence of infectious diseases that are not an identified problem on the mainland including K. pneumoniae and Uncinaria spp. (hookworm). These pathogens may contribute to early pup mortality and those pups that survive may be negatively affected into adulthood, however both infections may be amenable to conservation management intervention.
The pilot investigation into stillborn pups relied heavily on histopathology and identification of inflammatory lesions in archived tissues as a method of screening for multiple pathogens. In the future, molecular testing would be useful for identifying specific pathogens. Molecular techniques would complement histological screening in testing placental tissue for pathogens such as C. burnetii as PCR is significantly more sensitive than identification of gross and histologic lesions of placentitis (Duncan et al., 2012). In combination with further work in defining the role of disease in stillbirth,
additional field protocols are recommended, including collection of frozen and formalin-fixed placental tissue from stillborn pups to allow more extensive analysis at a later date. These measures will maximise the chances of reaching a diagnosis in cases of late gestational and peripartum mortality and improve our understanding of the factors involved in pup mortality. Further, examination of hormonal profiles of adult female NZ sea lions with collection of appropriately timed serum samples would be important to investigate pregnancy rates and the presence and magnitude of early embryonic loss. Progesterone measurement in serial blood samples has been reported as an accurate technique to estimate pregnancy rates and identify rates of embryonic loss in South African fur seals (Arctocephalus pusillus; Guinet et al., 1998) and NZ fur seals (McKenzie et al., 2005), however pregnant and non-pregnant animals cannot be distinguished until after implantation of the embryo after diapause. In NZ sea lions this is estimated to be approximately June, during which time sampling is practically difficult due to limited access and poor weather conditions at remote sub- Antarctic colonies and dispersal of females for foraging.
The finding of strong and persistent T. gondii seropositivity in several NZ sea lion females at Otago Peninsula and Stewart Island warrants surveillance for clinical effects and opportunistic retesting of serum where possible. The work presented in this thesis shows that both tests evaluated (LAT and ELISA), but particularly the LAT produced reliable results and could be used for surveillance in NZ sea lions, with further validation of the test as sample size increases.
Although parenteral ivermectin administration has been the most widely used in pinnipeds, other routes should be considered to minimise pup handling, therefore reducing the risk of stress and injury to animals. Ivermectin has been used frequently and effectively in domestic species to treat internal and external parasites as a topical pour-on preparation (Bisset et al., 1990, Pagé et al., 2000) with standard absorption and efficacy in all weather conditions that may be encountered in the sub- Antarctic, including rain immediately after application (Rolfe et al., 1997). Other endectocides such as selamectin are commonly used topically on domestic small animals of comparable size and weight
to NZ sea lion pups and have been shown in dogs and cats to be highly effective at removing internal and external parasite burdens with a wide safety margin (Bishop et al., 2000) while avoiding potential complications associated with injection of anti-parasitic drugs. Aside from its effective use for heartworm prophylaxis in red pandas in China (Lan et al., 2012), no reports have been published using selamectin in non-domestic animal species and any use in NZ sea lions would be off-label, however with research into its effects and pharmacokinetics it could provide a simple, effective and safe route of medicating pups to remove hookworm burdens. Efficacious removal of hookworm burdens in pups could also be achieved by treatment of pregnant adult females to break the life cycle before the lactogenic transmission phase. Complete removal of canine hookworm (Ancylostoma caninum) infection of domestic dog pups (also transmitted by the transmammary route) has been demonstrated by treatment of pregnant bitches with a single dose macrocyclic lactone (eg. doramectin, moxidectin; Schnieder et al., 1994, Epe et al., 1999). This may be a promising option for the treatment of sea lion pups. A large trial is recommended to further evaluate the benefits of worm burden removal in NZ sea lion neonates and assess environmental impacts beyond the intended host, particularly on invertebrates.
Overall the findings presented in this thesis show no evidence for infectious disease as a major impact on gestational and peripartum reproductive success. In contrast, some data presented particularly in Chapter Four has alluded to the influence of K. pneumoniae and Uncinaria spp. on pup and juvenile mortality, an area which should be carefully examined to understand pathogen dynamics in order to implement mitigation attempts. Planned work to address this knowledge gap involves a case control trial to identify risk factors involved in pup mortality including environmental factors (weather, substrate, habitat type), maternal factors (parity, age), pup factors (sex, age, external wounds, K. pneumoniae infection) and management factors (tagging, ivermectin treatment). Results from this study will direct future mitigation effort toward the strongest drivers of mortality.