Incidence, pathology and involvement of Nasitrema sp. in odontocete strandings

Abstract

Toe genus Nasitre'ina (Trematoda, Digenea)nafbeen implicated in causing odontocete strandings and ddth. This trematode, located principally in the paraotic sinuses, has been decribed affecting the ear and the brain. Although considered pathogenic, a thorough description of the resulting lesions is lacking. Toe presence and pathological processes of Nasitrema sp. • in several odontocete species are presented and the involvement of this parasite in strandings is discussed. Routine necropsies are conducted on the cetaceans stranded on the Canary lslands coasts, paying special attention to the parasitism of the otic region. During the last two years, a high percentage of the carcasses examined, of more than four odontocete species, had this trematode present in the paraotic sinuses. Toe parasite was found to have caused lesions ranging f rom mild sinusitis to severe meningo-encephalitis even associated with abscesses affecting the nervous tissues. Toe latter occurred in an old Tursiops truncatus severely infested and showing adult flukes migrating through the eight cranial nerve. Toe histopathology showed a moderate reaction to both adults and eggs, characteristic of the predominance of round inflammatory cells resulting in neuritis, meningo-encephalitis and malacia. In other cases, with the same lesions, no parasitic fotms were found. Toe cases observed allow us to discuss the pathogenicity of Nasitrema sp. affecting the central nervous system which may imply an equilibrium dysfunction inducing the odontocete to strand. From a pathological perspective, the absence of parasitic forms does not rule out its participation in nervous lesions, thus supporting the present results which clearly indicate a higher incidence of this parasite than reported, mainly because it is overlooked in most necropsies.