Abstract

Lungworm infection affects both captive and free-ranging marine mammals and can lead to morbidity and mortality by causing parasitic pneumonia, bronchitis, secondary infection, and even airway obstruction under heavy burden.¹ Lungworms are commonly found in different species of stranded cetaceans around the world, with effects ranging from subclinical or self-limiting infections to a contributor to natural mortality in wild populations.^2,3 Lungworm infection has been documented to cause severe pathology and mortality in Indo-Pacific finless porpoise Neophocaena phocaenoides (NP), particularly in younger individuals; therefore, it may implicate the population survival of this species is affected by multiple anthropogenic stressors.^4,5

Postmortem computed tomography (PMCT) is an emerging technique used in the postmortem examination of humans and animals.⁶ Since 2014, Kot and his team started the routine application of PMCT in cetacean stranding investigation in Hong Kong, which has since been increasingly used in stranding programmes globally.^7,8 For example, PMCT was used to investigate the lungs of stranded harbour porpoises and can characterise pulmonary pathologies including lungworm infection.⁸ We have also previously demonstrated that PMCT is an effective tool to characterise different parasitic infections in stranded cetaceans, which can assist in pathological assessment and guide sampling during necropsy, as well as facilitate studies on the epidemiology and health impacts of parasitic infection in wild cetaceans.^9,10

In the current study, we report the comprehensive findings from our virtopsy-led postmortem investigation in Hong Kong, focusing on lungworm infection in stranded Indo-Pacific finless porpoise (Neophocaena phocaenoides, NP). This study analysed the postmortem findings from 125 NP stranded between March 2014 and August 2022, including PMCT, necropsy, and parasitological findings. Two species of lungworms of the genus Halocercus were recovered and identified as H. sunameri and H. pingi. Lungworm infections by these two species had different presentations characterised in PMCT and necropsy, with the former presented as well-defined, isoattenuated-to-hyperattenuated nodules in the lung parenchyma, and the latter presented as ill-defined, heterogeneously isoattenuated lesions in the parenchyma and can also occupy and occlude the airways. We observed that H. pingi was only found in younger unweaned individuals and often caused severe parasitic pneumonia, whereas H. sunameri was generally associated with limited pathology despite variable parasitic burdens. Overall, the estimated prevalence of lungworm infection in stranded NP was 73.6% (n=92/125). This study updates our limited understanding on parasitic infections in NP which can be a significant contributor to their natural mortality, as well as demonstrates that PMCT is useful in stranding investigation to characterise pathology and health threats in stranded cetaceans.

Acknowledgements

We would like to thank the Agriculture, Fisheries, and Conservation Department of the Hong Kong Special Administrative Region Government for the continuous support in this project. Sincere appreciation is extended to the veterinarians, staff, and volunteers from the Ocean Park Conservation Foundation Hong Kong, the Marine Mammal Department of Ocean Park Hong Kong, as well as the Aquatic Animal Virtopsy Lab, City University of Hong Kong. This project is financially supported by the Marine Conservation Enhancement Fund (grant no.: MCEF20007), the CityU Strategic Research Grant (grant no.: CityU 11104721), and the Marine Ecology Enhancement Fund (grant no.: MEEF2019010, MEEF2019010A, MEEF2019010B), the Marine Ecology & Fisheries Enhancement Funds Trustee Limited. Any opinions, findings, conclusions, or recommendations expressed herein do not necessarily reflect the views of the Marine Ecology Enhancement Fund or the Trustee; and views of HKLTL, CAPCO, and HK Electric, and the Marine Conservation Enhancement Fund.

*Presenting author

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