Neonatal anaemia is a phenomenon observed commonly in many species. For pinniped pups, this anaemia has generally been attributed to physiological responses to host-environment changes such as the increased oxygen availability post-partum, compared to the in utero environment, and the expansion of plasma volume with growth. However, despite the widespread host distribution of haematophagous hookworm and lice species, few studies have considered parasitosis as a cause of anaemia in pinniped pups. In this study, we investigated the impact of hookworm (Uncinaria sanguinis) and lice (Antarctophthirus microchir) infections on the health status of free-ranging neonatal Australian sea lion pups (Neophoca cinerea; n=295) by estimating their effects on haematological parameters. Additionally, in order to determine whether these parasites are simply correlated with the occurrence of neonatal anaemia or play a causative role in its development, we experimentally manipulated naturally-occurring infections and compared changes in the haematological values between ivermectin-treated pups (n=31) and saline-treated pups (n=24).
Key findings of this study include the identification of U. sanguinis as an important agent of disease for neonatal N. cinerea pups, with infection causing significant anaemia, hypoproteinaemia, and a predominantly lymphocytic-eosinophilic systemic inflammatory response. Conversely, A. microchir has a lesser impact on N. cinerea pup health with infestation causing mild anaemia and hyperproteinaemia; high intensities of lice are likely secondary to hookworm infection or other causes of disease. Critically, by classifying the erythroid response to anaemia as regenerative, we demonstrated that anaemia is not solely a benign physiological response to host-environment changes, but largely reflects a significant pathological process in this species. These findings inform the conservation management of free-ranging N. cinerea and improve our understanding of the impact of parasitic infections on the health and development of haematological parameters in pinniped pups.