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Diseases of Aquatic Organisms

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DAO 139:93-102 (2020)  -  DOI: https://doi.org/10.3354/dao03468

Cranial crassicaudiasis in two coastal dolphin species from South Africa is predominantly a disease of immature individuals

Marie-Francoise Van Bressem1,*, Pádraig Duignan2, Juan Antonio Raga3, Koen Van Waerebeek1,4, Natalia Fraija-Fernández3,5, Stephanie Plön6

1Cetacean Conservation Medicine Group, Peruvian Centre for Cetacean Research, Museo de Delfines, Lima 20, Peru
2Department of Veterinary Sciences, The Marine Mammal Center, 2000 Bunker Road, Sausalito, California 94965, USA
3Marine Zoology Unit, Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia, PO Box 22085, 46071 Valencia, Spain
4Center for Chinese White Dolphin Research and Conservation, Beijing Institute of Technology at Zhuhai, 6 Jinfeng Road, Zhuhai City, 51900 Guangdong, PR China
5Department of Life Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK
6Earth Stewardship Science Research Institute-African Earth Observatory Network (AEON), Nelson Mandela University, South Campus, Port Elizabeth 6031, South Africa
*Corresponding author:

ABSTRACT: Crassicauda spp. (Nematoda) infest the cranial sinuses of several odontocetes, causing diagnostic trabecular osteolytic lesions. We examined skulls of 77 Indian Ocean humpback dolphins Sousa plumbea and 69 Indo-Pacific bottlenose dolphins Tursiops aduncus, caught in bather-protection nets off KwaZulu-Natal (KZN) from 1970-2017, and skulls of 6 S. plumbea stranded along the southern Cape coast in South Africa from 1963-2002. Prevalence of cranial crassicaudiasis was evaluated according to sex and cranial maturity. Overall, prevalence in S. plumbea and T. aduncus taken off KZN was 13 and 31.9%, respectively. Parasitosis variably affected 1 or more cranial bones (frontal, pterygoid, maxillary and sphenoid). No significant difference was found by gender for either species, allowing sexes to be pooled. However, there was a significant difference in lesion prevalence by age, with immature T. aduncus 4.6 times more likely affected than adults, while for S. plumbea, the difference was 6.5-fold. As severe osteolytic lesions are unlikely to heal without trace, we propose that infection is more likely to have a fatal outcome for immature dolphins, possibly because of incomplete bone development, lower immune competence in clearing parasites or an over-exuberant inflammatory response in concert with parasitic enzymatic erosion. Cranial osteolysis was not observed in mature males (18 S. plumbea, 21 T. aduncus), suggesting potential cohort-linked immune-mediated resistance to infestation. Crassicauda spp. may play a role in the natural mortality of S. plumbea and T. aduncus, but the pathogenesis and population level impact remain unknown.


KEY WORDS: Sousa plumbea · Tursiops aduncus · South Africa · Crassicauda spp. · Cranialosteolysis · Parasitosis


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Cite this article as: Van Bressem MF, Duignan P, Raga JA, Van Waerebeek K, Fraijia-Fernández N, Plön S (2020) Cranial crassicaudiasis in two coastal dolphin species from South Africa is predominantly a disease of immature individuals. Dis Aquat Org 139:93-102. https://doi.org/10.3354/dao03468

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