Epidemiological and pathological analysis of cranial crassicaudasis in stranded cetaceans in the Canary Islands

Abstract

This retrospective study focuses on 55 out of 852 (6.45%) cetaceans stranded in the Canary Islands over a 25-year period, from 1999 to 2023, which presented parasitic infestation of the pterygoid sacs, which could be an important morbidity factor due to the intimate and close connection between the air sacs, the tympanic bullae, and the acoustic nerves. From these, nematodes of the genus Crassicauda were observed in 39 animals (71%), with different levels of severity (classified into mild, moderate and severe) and with our without co-infection with other nematodes (Stenurus spp.) and/or trematodes (Nasitrema spp.). The epidemiological study allowed us to identify that the incidence was higher in Stenella frontalis (26%) and Grampus griseus (21%) species in addition with more severe level of parasitization. The prevalence was higher in the juvenile/subadults age group (55%), while regarding the sex, we found the same proportion in males and females. In addition, due to the lack of gross descriptions in most cases of parasitic sinusitis, we aimed to histologically characterize the effect of parasitic infestation on the tissues of the pterygoid sacs. For this purpose, histological samples from apparently non parasitized pterygoid sacs from 2 cetaceans were analysed; describing the normal histological features of the sacs, which were compared with the histological samples from 3 cetaceans that had Crassicauda sp. in the pterygoid sacs at the time of necropsy. As a result of the parasitization, a mild inflammatory reaction, hyperkeratosis, and desquamation of the pseudostratified columnar epithelium was observed. Since migration of nematode parasites to the central nervous system (CNS) can occur under certain circumstances, causing damage or serving as a vector of pathogenic microorganisms (e.g. Brucella spp.), we looked for brain lesions and associated-pathogens described in their anatomopathological reports to relate them with the presence and level of parasitization by Crassicauda sp. in the pterygoid sacs. No relationship was found between the presence of Crassicauda sp. and any of the pathological agents (morbillivirus, herpesvirus, Brucella spp. and Toxoplasma gondii) detected in the CNS when the cetaceans were tested for.