Neuronal and astrocytic involvement in striped dolphins (Stenella coeruleoalba) with morbilliviral encephalitis

Dolphin morbillivirus (DMV), a highly pathogenic agent, may cause peculiar, "brain-only" forms of infection (BOFDI), in which viral antigen and/or genome is found exclusively in the brain from striped dolphins (Stenella coeruleoalba). These BOFDIs show morphopathological similarities with subacute sclerosing panencephalitis and old dog encephalitis (ODE) in measles virus-infected patients and in canine distemper virus-infected dogs, respectively. The brain tissue from 3 BOFDI-affected striped dolphins was investigated by means of double labelling-indirect immunofluorescence (DL-IIF) and ultrastructurally, in order to characterize the DMV-targeted neuronal and non-neuronal cell populations, along with the associated submicroscopic findings. Viral colonization of calbindin-immunoreactive (IR) and nitric oxide synthase-IR neurons was detected in the cerebral parenchyma from the 3 DMV-infected dolphins under study, associated with nuclear (chromatin) and cytoplasmic (mitochondrial) ultrastructural changes. Furthermore, a limited viral targeting of brain astrocytes was found in these animals, all of which exhibited a prominent astrogliosis/astrocytosis. To the best of our knowledge, those herein reported should be the first submicroscopic pathology and neuropathogenetic data about BOFDI in striped dolphins. In this respect, the marked astrogliosis/astrocytosis and the low viral colonization of brain astrocytes in the 3 DMV-infected dolphins under investigation are of interest from the comparative pathology and viral neuropathogenesis standpoints, when compared with ODE-affected dogs, in whose brain a non-cytolytic, astrocyte-to-astrocyte infectious spread has been recently documented. Further studies aimed at characterizing the complex DMV-host interactions in BOFDI-affected striped dolphins are needed.