Localization of viral antigens and brain ultrastructural findings in striped dolphins (Stenella Coeruleoalba) with “brain-only” dolphin morbillivirus infection.

Introduction: Dolphin Morbillivirus (DMV), a highly pathogenic agent, may cause peculiar, “brain-only” forms of infection (BOFDI) in which viral antigen/genome is found exclusively in the brain from striped dolphins (Stenella coeruleoalba). These BOFDIs show morphopathological and neuropathogenetic similarities with Subacute Sclerosing Panencephalitis and Old Dog Encephalitis in Measles Virus-infected patients and in Canine Distemper Virus-infected dogs, respectively. Materials and Methods: The brain from 3 BOFDI-affected striped dolphins was investigated ultrastructurally and by double-labeling indirect immunofluorescence (IIF), in order to characterize the submicroscopic findings and the DMV-targeted neuronal and non-neuronal cell populations. Results: Alongside with nuclear (chromatin) and cytoplasmic (mitochondrial) ultrastructural changes, we were able to demonstrate viral colonization of calbindin-immunoreactive (IR) and nitric oxide synthase-IR neurons in the brain from the 3 DMV-infected dolphins under study. Furthermore, a limited astrocytic colonization was found in these 3 animals, all of which exhibiting a prominent astrogliosis/astrocytosis. Conclusions: To our knowledge, these should be the first submicroscopic and neuropathogenetic data about BOFDI in striped dolphins. In this respect, the marked astrogliosis/astrocytosis and the reduced DMV colonization of astrocytes in the 3 dolphins under study are of interest from the comparative pathology and from the viral neuropathogenesis standpoints when compared to ODE-affected dogs, in whose brain a non-cytolytic, astrocyte-to-astrocyte infection’s spread has been reported. Further studies aimed at characterizing the complex DMV-host interactions in BOFDI-affected striped dolphins are absolutely needed. Footnote: Research Project financially supported by the Italian Ministry for the Environment (“Le Sentinelle del Mare”; Scientific coordinator: Prof. Giovanni Di Guardo).