Search

The Australian sea lion (Neophoca cinerea) experiences high pup mortality of seasonally alternating severity, partly attributed to endemic hookworm (Uncinaria sanguinis) infection. To further explore health outcomes of early hookworm elimination, a treatment trial was conducted at Seal Bay Conservation Park, South Australia, over consecutive lower and higher mortality breeding seasons (2019, 19.2%; 2020–1; 28.9%). Pups (n = 322) were stratified into two age cohorts (median 14 d and 24 d recruitment ages) and randomly assigned to treated (topical ivermectin 500 μg/kg) or control (untreated) groups. A younger prepatent cohort a posteriori. A seasonally independent growth benefit resulted from hookworm elimination across all age cohorts. The greatest relative improvements (bodyweight + 34.2%, standard length + 42.1%; p ≤ 0.001) occurred in the month post-treatment, in the youngest prepatent cohort. A significant benefit of lesser magnitude (bodyweight + 8.6–11.6%, standard length + 9.5–18.4%; p ≤ 0.033) persisted up to 3 months across all age cohorts – greatest in the youngest pups. Treatment resulted in immediate improvement in hematological measures of health – decreased anemia and inflammation severity (p ≤ 0.012). These results enhance our understanding of host–parasite–environment interactions within the context of hematological ontogenesis, confirm the seasonally independent benefits of hookworm disease intervention, and further inform conservation recommendations for this endangered species.

Toxoplasma gondii is a ubiquitous parasite increasingly detected in marine mammals and suspected to contribute to limited recovery of endangered populations. This study reports on the exposure of the Australian sea lion (Neophoca cinerea) to this protozoon using archived adult and pup sera from three island colonies in South Australia. Modified agglutination testing (MAT) detected a seroprevalence of 30.4% (95% CI 13.2-52.9: n = 23) and high antibody titers (512 to > 2048 IU/ml) in adult females (median age 9.5 y, range 5.5-14.5 y) at Dangerous Reef, a felid-free island. Antibodies weren’t detected in any surveyed pup (97.5% CI 0.0-2.0%, n = 184) at two felid-free islands (Dangerous Reef: n = 21; Olive Island: n = 65), nor at Kangaroo Island (n = 98), which has a high-density feral cat population. Kangaroo Island pups of known age were 7-104 d old, while standard length and bodyweight comparison suggested younger and older pup cohorts at Dangerous Reef and Olive Island, respectively. This study provides the first quantification of disease risk in this endangered species from T. gondii exposure. The absence of detectable pup seroconversion supports the lack of detectable congenital transmission, maternal antibody persistence or early post-natal infection in the sampled cohort yet to commence foraging. An extended serosurvey of N. cinerea colonies is recommended to confirm the hypothesis of predominantly forage-associated exposure to T. gondii in this species. Findings have implications for parasitic disease risk in wildlife inhabiting Australia’s islands and for the feral cat control program on Kangaroo Island.