The Pathology of Cetacean Morbillivirus Infection and Comorbidities in Guiana Dolphins During an Unusual Mortality Event (Brazil, 2017-2018).

Cetacean morbillivirus (CeMV; Paramyxoviridae) is the most significant pathogen of cetaceans worldwide. The novel "multi-host" Guiana dolphin (Sotalia guianensis; GD)-CeMV strain is reported in South American waters and infects Guiana dolphins and southern right whales (Eubalaena australis). This study aimed to describe the pathologic findings, GD-CeMV viral antigen distribution and detection by RT-PCR (reverse transcriptase polymerase chain reaction), and infectious comorbidities in 29 Guiana dolphins that succumbed during an unusual mass-mortality event in Rio de Janeiro state, Brazil, between November 2017 and March 2018. The main gross findings were lack of ingesta, pulmonary edema, ascites, icterus, hepatic lipidosis, multicentric lymphadenomegaly, as well as pneumonia, polyserositis, and multiorgan vasculitis caused by Halocercus brasiliensis. Microscopically, the primary lesions were bronchointerstitial pneumonia and multicentric lymphoid depletion. The severity and extent of the lesions paralleled the distribution and intensity of morbilliviral antigen. For the first time in cetaceans, morbilliviral antigen was detected in salivary gland, optic nerve, heart, diaphragm, parietal and visceral epithelium of glomeruli, vulva, and thyroid gland. Viral antigen within circulating leukocytes suggested this as a mechanism of dissemination within the host. Comorbidities included disseminated toxoplasmosis, mycosis, ciliated protozoosis, and bacterial disease including brucellosis. These results provide strong evidence for GD-CeMV as the main cause of this unusual mass-mortality event.

Guiana Dolphin Unusual Mortality Event and Link to Cetacean Morbillivirus, Brazil.

During November-December 2017, a mass die-off of Guiana dolphins (Sotalia guianensis) began in Rio de Janeiro, Brazil. Molecular and pathologic investigations on 20 animals indicated that cetacean morbillivirus played a major role. Our findings increase the knowledge on health and disease aspects of this endangered species.