Browsing by Author "Michael SA"

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    Clinical parameters of hypervirulent Klebsiella pneumoniae disease and ivermectin treatment in New Zealand sea lion (Phocarctos hookeri) pups
    (PLOS, 2022-03-03) Michael SA; Hayman DTS; Gray R; Roe WD; Raverty S
    Hypervirulent Klebsiella pneumoniae infection causes significant mortality of endangered New Zealand sea lion pups at Enderby Island, Auckland Islands. Gross necropsy and histopathology findings are well reported, but little is known about the clinical course of disease in affected pups. To determine factors feasible as clinical screening tools for hypervirulent K. pneumoniae in live pups, 150 pups over two field seasons (2016-18) were recruited shortly after birth for a prospective cohort study. A randomised controlled clinical treatment trial with the anthelmintic ivermectin was conducted concurrently and risk factor data and biological samples were collected approximately fortnightly. Treatment with ivermectin has been demonstrated to reduce the risk of hypervirulent K. pneumoniae mortality in pups, so effects on clinical parameters between the treated and control cohorts were also investigated. A broader sample of pups were monitored for clinical signs to investigate the course of disease in affected pups. Clinical signs, haematology and oral and rectal swabs to detect gastrointestinal carriage of hypervirulent K. pneumoniae were not useful for detection of disease prior to death. Of those pups that died due to hypervirulent K. pneumoniae, only 26.1% (18/69) had any clinical signs prior, likely a reflection of the peracute course of disease. On comparison of haematological parameters between ivermectin-treated and control pups, significantly lower total plasma protein and higher eosinophil counts were seen in control versus treated pups, however standard length as a surrogate for age was a more important influence on parameters overall than ivermectin treatment. This study also highlighted a cohort of pups with severe clinical signs suggestive of hypervirulent K. pneumoniae infection were lost to follow up at the end of the monitored season, which could be contributing to cryptic juvenile mortality.
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    Risk Factors for New Zealand Sea Lion (Phocarctos hookeri) Pup Mortality: Ivermectin Improves Survival for Conservation Management
    (Frontiers Media S.A., 2021-07-09) Michael SA; Hayman DTS; Gray R; Roe WD; Davis RW
    Septicaemia due to hypervirulent (HV) Klebsiella pneumoniae is the leading cause of neonatal pup mortality in endangered New Zealand sea lions (Phocarctos hookeri) at Enderby Island, in the New Zealand sub-Antarctic. Accounting for approximately 60% of annual pup mortality at this site following an epizootic event in 2001–02, HV K. pneumoniae is also emerging worldwide as a significant community-acquired human pathogen. To facilitate efficient direct mitigation to reduce pup mortality, a case-control study and prospective cohort study were conducted to identify risk factors amenable to active management. Additionally, to investigate impacts of hookworm (Uncinaria spp.), a nested treatment trial with the anthelmintic ivermectin was undertaken concurrently. During two austral summer field seasons (2016–2018), 698 pups were captured for treatment trial recruitment and the collection of morphometric measurements, biological samples and risk factor data. Gastrointestinal carriage of the virulent phenotype of K. pneumoniae was a consistent risk factor, while ivermectin treatment and higher body condition index consistently reduced risk of HV K. pneumoniae mortality. Significantly fewer ivermectin-treated pups were found dead (24.1% control, 11.1% treatment), with a trend towards a higher proportion of HV K. pneumoniae deaths amongst the control group. This study provides evidence to support ivermectin treatment as a pup mortality mitigation strategy in New Zealand sea lions at Enderby Island. If applied to larger colonies where HV K. pneumoniae and hookworm impact pup survival, this intervention could have population-scale benefits for this endangered species. Further work is required to understand how ivermectin prevents HV K. pneumoniae septicaemia, but removal of hookworms before intestinal mucosal damage occurs could limit systemic spread of virulent bacteria from the gastrointestinal tract.