Systemic toxoplasmosis in striped dolphins stranded in the Canary Islands

Abstract

Toxoplasma gondii is considered a major cause of death and encephalitis in marine mammals (Dubey et al., 2003), as well as is a reflection of the increased level of aquatic pollution (Dubey et al., 2020). We present, for the first time, T. gondii infection in striped dolphins (Stenella coeruleoalba) stranded in the Canary Islands. Between 2000 and 2020, 1183 cetaceans were found stranded in the Canary coasts, 217 of them belonging to the species Stenella coeruleoalba, of which 167 were subjected to a complete anatomopathological study, two of them being relevant in our study. Both animals (two males; adult and subdadult, respectively) showed poor body condition and lesions consistent with multiorgan necrosis and lymphohistiocytic inflammation with intralesional protozoa; specifically in the central nervous system, heart, rete mirabile, adrenal glands, pancreas, liver, lung, spleen and pituitary gland. However, in the adult specimen, chronic lymphoplasmacytic interstitial bronchopneumonia and multinodal follicular depletion with reactive lymphoid hyperplasia of the laryngeal and pharyngeal tonsils were also found. Meanwhile, in the subadult specimen, necrosis in the adenohypophysis, multinodal follicular depletion, focal ulcerative glossitis, focal ulcerative gastritis, multiorgan parasitosis and fractures in the mandible and tympanic-periotic complex, possibly caused by previous trauma, were also found. Despite the presence of other findings, the main lesions were compatible with systemic toxoplasmosis, as the cause of death in these striped dolphins. The identification of T. gondii was confirmed by molecular methods. However, morbillivirus nucleic acid was not detected in the tissues of any of the dolphins, supporting the hypothesis that this protozoan played a primary etiologic role in the development of severe lesions in cetaceans. This study therefore describes in detail the histopathological findings associated with T. gondii parasitosis in two striped dolphins and report severe extensive coagulative necrosis in the pancreas and the pituitary gland, two lesions not previously reported in cetaceans toxoplasmosis.