Pyogranulomatous encephalitis associated with cerebral trematodiasis in a Blainville´s beaked whale (Mesoplodon densirostris)

Abstract

A 454 cm length and 814 kg weight, adult female Blainville ́s beaked whale (Mesoplodon densirostris), was found death in Fuerteventura, Canary Islands. A complete necropsy was performed. The animal was in a poor body condition and the carcase was fresh. The most relevant finding during the necropsy was a severe chronic-active multifocal pyogranulomatous encephalitis. Macroscopically, multifocal, tortuous, irregular, well-defined, yellow-green lesions, between 1.3x2 and 4x3.5 cm sized, affecting the cerebral cortex parenchyma of the orbital lobe and thalamus. Histologically, multiple areas of encephalomalacia, granulation tissue, multifocal haemorrhages with intralesional adult trematode parasites (evident cuticle, musculature with calcareous corpuscles, without a pseudocelomic cavity and a differentiated digestive tract) and triangular refringent yellow eggs. Additional histopathological changes observed in the central nervous system (CNS) were: diffuse gliosis, multifocal perivascular cuffs, perivascular edema and multifocal presence of cholesterol crystals. Other pathological findings suggested an alive stranding episode. In cetaceans, different species of the genus Nasitrema have been described in the pterygoid sacs, but occasionally they can migrate through the vestibulocochlear nerve to the encephalon, causing encephalitis. In the Canary Islands, trematodes have been described in the CNS of seven species of odontocetes. Molecular studies (qPCR) detected Nasitrema spp. in frozen SNC samples, finding a higher homology with N. delphini (99%). To the best of our knowledge, the present case represents the first description of a cerebral trematodiasis by Nasitrema sp. in a member of the Ziphiidae family.