Nematodal otitis by Stenurus globicephalae in a melon-headed whale (Peponocephala electra) stranded in Northeastern Brazil: case report and literature update

Cetaceans are highly adapted marine mammals whose survival depends on precise auditory and echolocation systems. Therefore, disease processes affecting these systems, including parasitic infections pose significant morbidity and may result in stranding and death. Here, we describe the pathologic and parasitological findings in an adult, male melon-headed whale ( Peponocephala electra ) stranded dead on the Brazilian coast. The main gross pathologic findings consisted of bilateral otitis media associated with myriads of nematodes in the tympanic bullae that occluded the tympanic lumen and resulted in compression of the tympanic membrane. Additional parasite-induced lesions were observed in the gastric and colonic mucosa, and in the skeletal muscle. Other relevant gross findings were abdominal effusion, visceral congestion, pulmonary petechiae, and lack of ingesta. Histopathologic examination of the tympanic membrane and middle ear soft tissue revealed chronic otitis and myringitis with epithelial hyperplasia and multifocal ulceration with intralesional nematodes. These nematodes were morphologically identified as Stenurus globicephalae through direct microscopy and electron microscopy analyses. In this case, severe parasitism of the tympanic apparatus was considered the primary pathologic condition. We surmise that the severity of the lesions noted in the auditory system could have resulted in disorientation and stranding, and, together with the physiological stress response associated with live stranding, ultimately led to death in this individual. This report underscores the role of parasitic otitis caused by S. globicephalae as a differential etiological diagnosis for stranding and death in cetaceans along the Brazilian coast and provides an updated overview of the literature on otic parasitism in cetaceans.