Causes of neonatal mortality in the New Zealand sea lion (Phocarctos Hookeri) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Pathology at Massey University, Palmerston North, New Zealand
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Date
2006
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Massey University
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Abstract
As part of a health survey of New Zealand sea lions (Phocarctos hookeri) on Enderby Island,
Auckland Islands (50°30’S, 166°17’E), neonatal mortality was continuously monitored at the
Sandy Bay Beach rookery, from 1998/1999 to 2004/2005. The primary causes of death were
categorised as trauma (35%), bacterial (24%) and hookworm (13%) infections, starvation (13%)
and stillbirth (4%). During the 2001/2002 and 2002/2003 breeding seasons, bacterial epidemics
caused by Klebsiella pneumoniae increased mortality by three times the mean in non-epidemic
years.
Uncinaria spp. from New Zealand sea lion (NZSL) pups was described for the first time using
morphometric criteria. It differed from the two species already described in pinnipeds, Uncinaria
lucasi and Uncinaria hamiltoni, suggesting the existence of a different morphotype in NZSLs. A
study on the epidemiology of hookworm infection showed that all pups up to at least three months
of age harboured adult hookworms in their intestines and transmammary transmission was
identified as the route of infection of NZSL pups. Uncinariosis as a primary cause of mortality was
generally associated with anaemia, haemorrhagic enteritis and frank blood in the lumen. The
relationship between hookworm burden and clinical disease could not be clearly established.
The 2001/2002 and 2002/2003 bacterial epidemics at Sandy Bay Beach rookery were caused
by a clonal strain of Klebsiella pneumoniae as verified by pulse-field gel electrophoresis and
antimicrobial testing. Suppurative arthritis was the most common post-mortem diagnosis during
the two epidemic seasons. Internal lesions were consistent with septicaemia, which
explained the wide range of organs from which the pathogen was grown in pure culture. A
serological test investigating the exposure of NZSLs to Klebsiella spp. showed that the large
majority of pups up to two months of age did not have any anti-Klebsiella antibodies, even after
the epidemics, but that almost all the adults were seropositive. In addition, passive
immunoglobulin (Ig) transfer from lactating females to neonates was examined by measuring IgG
levels in pups and was very low compared to terrestrial mammals although similar to other
pinniped neonates.
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Keywords
New Zealand sea lion, Phocarctos hookeri, Pathology, Seal pups, Hookworms, Klebsiella pneumoniae