Research and characterization of Morbiliviruses of cetaceans in Brazil

Abstract

The genus Morbillivirus (Paramyxoviridae family, Mononegavirales order) shows single-stranded RNA and consists of antigenically related species, including the human measles, canine distemper, rinderpest and peste des petits ruminants, among others. They are characterized by acute infection, high transmissibility and high mortality rates. Since 1988, when Morbillivirus infection was discovered in marine animals, more than 10 epizootic outbreaks with high mortality rates affected pinnipeds and cetaceans in the northern hemisphere, constituting a major natural threat to marine mammals. No one knows exactly what leads to the occurrence of these outbreaks. The main lesions associated with infection in marine mammals include severe bronchointerstitial pneumonia, non-suppurative meningoencephalitis and immunosuppression, favoring the occurrence of opportunistic viral infections (family Herpesviridae), parasite (Toxoplasma gondii), bacteria (Brucella spp.) and fungal infections (Aspergillus spp.). Although serological investigations indicate the presence of the virus in all major oceans, just recently fatal cases were recorded in the southern hemisphere, two in Australia and one in Brazil. The fatal case identified in a estuarine dolphin (Sotalia guianensis) in Brazil indicates that the virus is present on our coast, and raises concerns about the role of the agent in cases of mortality and the possibility of occurrence of epizootics. A comparison of partial sequences from a conserved region of the virus (P gene) showed that the variant identified in Brazil phylogenetically differs from the variants affecting cetaceans in the northern hemisphere, suggesting that it represents a new strain or a new lineage of cetacean morbillivirus. The overall objectives of this project, which has the collaboration of several national and international institutions, are to investigate the occurrence and characterize the morbillivirus infection in cetaceans from the Brazilian coast. Detection of the virus will be carried out by means of immunohistochemical staining using antibody against canine distemper virus, which cross-react with cetacean morbillivirus, as well as by RT-PCR using primers which amplify conserved regions of the viral genome. Markers of different regions of the viral genome will be used for the molecular characterization of a new variant of morbillivirus recently detected in Brazil. Serological tests will be performed to detect levels of antibodies in the serum of animals and infer epidemiological aspects. By means of histopathological techniques we will characterize microscopic changes and infection patterns of positively infected hosts. The data obtained here will elucidate phylogenetic aspects of the Morbillivirus present in our coast and infer on pathological and epidemiological aspects of cetaceans morbiliviruses in Brazil. (AU)