Abstract

An average of 32 stranded cetaceans are recovered from Hong Kong coastline every year and examined as part of the Hong Kong Marine Mammal Stranding Investigation Programme from the Agriculture Fisheries and Conservation Department. Over the period 2006 to 2011, 32% were Indo-Pacific humpbacked dolphins (Sousa chinensis), and 64% are finless porpoises (Neophocaena phocaenoides), the remaining being cetaceans in such decomposition that the species could not be determined grossly. Although still rudimentary, knowledge about the baseline health of this local population of cetaceans is important, as climate change, environmental degradation and other types of anthropogenic pressures may trigger disease emergence and epizootics. Coastal small cetaceans such as the two main species in Hong Kong waters are at particularly high risk for emerging diseases.

Pathogens affecting the reproductive tract and the mammary glands are particularly important as they may impact on reproductive success of wild populations. Mammary parasites such as Crassicauda spp. are able to cause severe mastitis, and have been suggested as having a potentially detrimental effect on reproduction in Atlantic white-sided dolphins¹ and bottlenose dolphins^4,5. This parasite affects a majority of mature female finless porpoises in Hong Kong. Lesions are associated with severe mastitis, calcifications and the presence of parasitic cysts and granulomas in the mammary glands and in adjacent muscles. Parasitic ova are found in mammary secretions and involvement of an intermediate host is not confirmed. Evaluating the effects of those parasites on lactation may provide insights into the fact that young of the year represent a high proportion of stranded Indo-Pacific humpbacked dolphins³ and finless porpoises² in Hong Kong.

Archived and prospective formalin fixed tissues and H&E stained slides from the two main species of interest, Sousa chinensis and Neophocaena phocaenoides are assessed. By histopathological examination, as well as review of records, photographs, gross necropsy observations, bacterial culture and additional diagnostic testing when indicated by findings, pathologies observed are described and categorised by system. A semi-quantitative histological scoring of mammary lesions caused by Crassicauda spp. is being used in this project to assess the potential detrimental role this parasite is playing in reproduction and neonatal survival of resident species of cetaceans in Hong Kong. Description of the lesions associated with the presence of this parasite will be useful to further characterise the pathogenicity and the life cycle of Crassicauda spp. in odontocetes.

Acknowledgements

The authors wish to thank the Agriculture, Fisheries and Conservation Department of The Government of Hong Kong, veterinary staff and clinical laboratory staff at Ocean Park Veterinary Centre and Ocean Park Conservation Foundation for their participation in this project. Attendance to the conference to present this work is supported by a grant from The Journal of Comparative Pathology Educational Trust.

References

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