In the summer of 1990 an epizootic
infection caused by a morbillivirus (DMV) killed several thousand striped dolphins (Stenella coeruleoalba) in the Mediterranean Sea. In 1991 and 1992 the epizootic reached Italian and Greek waters. The
infection by DMV in the acute period of the epizootic caused
encephalitis,
pneumonia and depletion of lymph nodes. After 1990, the systemic
infection apparently disappeared from the Catalonian coast, giving way to cases of
chronic infection of the CNS. Dolphins that died between 1991 and May 1994 were necropsied, and investigated for lesions due to DMV, and for the presence of morbillivirus
antigen in tissues.
Encephalitis occurred in 6 dolphins in which DMV
antigen was demonstrated in the CNS and which were without lesions or
antigen in other, non-nervous tissues. Inflammatory lesions,
gliosis, and DMV
antigen decreased in density and amount from cerebral grey matter, through the thalamic areas to the medulla oblongata. The cerebellum was usually spared. Lesions consisted of non-suppurative
encephalitis, with diffuse
gliosis and glial nodules and neuronophagia, and loss of neurons. Perivascular cuffing of lymphocytes and plasma cells was present in the cerebral cortex and the white matter beneath the cortex. Multinucleate syncytia were not detected in any of the dolphins. The haemagglutinin of DMV was detected mainly in neurons in the cerebral cortical areas. There was no clear relationship between the presence and amount of DMV
antigen and the density or chronicity of lesions. Viral inclusions were seen in haematoxylin and
eosin stained sections in 3/6 dolphins, principally in the nucleus and the cytoplasm of neurons. In the immunoperoxidase stained sections, dense granular deposits of chromogen, similar to viral inclusions, were evident in all 6 dolphins. The change in the distribution of lesions and of DMV
antigen, from systemic to localized in the CNS, and the clustering of systemic DMV
infections in the first four months of the epizootic, giving rise to sporadic occurrence of local
CNS infection in the subsequent four years, as well as the chronic nature of the CNS lesions, which closely resembles
subacute sclerosing panencephalitis, strongly support the existence of a chronic
morbillivirus infection in the striped dolphin, as a delayed consequence of the 1990 epizootic.