Abstract

Crassicauda spp. are in the genus of nematodes and could parasitize the skull of cetaceans, including the frontal-orbitosphenoid, pterygoid, and auditory regions.^3,4 Crassicauda spp. could produce glycosaminoglycan (GAG)-degrading enzymes to hydrolyze the GAG of extracellular matrix (ECM), and then cause irreversible trabecula-like lesions in the cetacean skull.³ Furthermore, the infestation of Crassicauda spp. also causes inflammatory response and damage to adjacent tissues, such as sinusitis, bone/soft tissue perforation, and degeneration of cranial nerves, and may thereby lead to mortality and stranding of cetaceans.^2,5 Crassicauda spp. infestation in cetacean skull have been reported worldwide.^1,3-5 However, current knowledge of Crassicauda spp. infestation in cetaceans around Taiwanese water is still scarce, and therefore a retrospective study is proposed.

Skull specimens of stranded/bycatch cetaceans, all held in the National Museum of Natural Science and National Taiwan Museum, were investigated for skull trabecula-like lesions. Lesions were categorized by severity (mild, moderate, and severe) and location (nasal, orbital, and auditory regions). Prevalences of skull trabecula-like lesions in the different cetacean species were calculated as the percentage of the number of affected skulls to the number of skulls investigated, and whether severities and locations of the lesions varied with cetacean species were examined by using chi-square tests.

In the present study, 339 skulls from 6 species including bottlenose dolphin (Tursiops spp.), Risso's dolphin (Grampus griseus), pantropical spotted dolphin (Stenella attenuata), spinner dolphin (Stenella longirostris), Fraser's dolphin (Lagenodelphis hosei), and rough-toothed dolphin (Steno bredanensis) were investigated. In total, 70 skulls had trabecula-like lesions (20.6%), and the prevalences ranged from 0% to 31.7% among different cetacean species. Stenella longirostris, L. hosei, and S. bredanensis were excluded from further statistical analysis due to low positive specimens. About 50% of skull trabecula-like lesions in low-prevalence species (< 20%; S. attenuata) were classified as severe severity and located at the nasal region, but more than 80% of the lesions in high-prevalence species (> 20%; Tursiops spp. and G. griseus) were classified as mild to moderate severity and located at the orbital and auditory regions. The prevalence, lesion severity, and location were different among these cetacean species, which could be associated with different subspecies of Crassicauda and susceptibility of different cetacean species. The skull trabecula-like lesions are irreversible and progressive, and hence the lesion severity should be directly correlated with the length of time after infection. The mild to moderate lesions located at the orbital and auditory regions in Tursiops spp. and G. griseus indicate they have died before the trabecula-like lesion progressing, which also indicates the Crassicauda spp. infestation in the orbital and auditory regions could be more harmful for cetacean health. In contrast, the severe lesions located at the nasal regions in S. attenuata are observed, indicating Crassicauda spp. infestation in nasal regions shows relative mild health effects. Therefore, it indicates 1) lesion locations of Crassicauda spp. in cetacean skulls is an important factor for host health; 2) Crassicauda spp. infestation is more harmful for Tursiops spp. and G. griseus rather than S. attenuata.

Acknowledgements

The authors thank Dr. Chiou-Ju Yao of the National Museum of Natural Science in Taichung, Taiwan; Dr. Jiun-Tsung Lin of National Taiwan Museum in Taipei, Taiwan; and Mr. Chi-hung Lin, Mr. Ming-Ching Lin, and Dr. Chieh Lo of the cetacean research laboratory, National Taiwan University, Taipei, Taiwan. Furthermore, the authors appreciate the Forestry Bureau, Council of Agriculture, for financial support of this project.

* Presenting author
⁺ Student presenter

Literature Cited

1.  Balbuena JA, Simpkin A. Role of Crassicauda sp. in natural mortality of pantropical spotted dolphins Stenella attenuata: a reassessment. Dis Aquat Organ. 2014;108:83–89.

2.  Morimitsu T, Kawano H, Torihara K, Kato E, Koono M. Histopathology of eighth cranial nerve of mass stranded dolphins at Goto Islands, Japan. J Wildl Dis. 1992;28:656–658.

3.  Pascual S, Abollo E, Lopez A. Elemental analysis of cetacean skull lesions associated with nematode infections. Dis Aquat Organ. 2000;42:71–75.

4.  Van Bressem MF, Van Waerebeek K, Montes D, et al. Diseases, lesions and malformations in the long-beaked common dolphin Delphinus capensis from the Southeast Pacific. Dis Aquat Organ. 2006;68:149–165.

5.  Zucca P, Di Guardo G, Pozzi-Mucelli R, Scaravelli D, Francese M. Use of computer tomography for imaging of Crassicauda grampicola in a Risso's dolphin (Grampus griseus). J Zoo Wildl Med. 2004;35:391–394.