Unusual striped dolphin mass mortality episode related to cetacean morbillivirus in the Spanish Mediterranean Sea

Abstract

Between March and April 2011, 37 dolphins stranded along the Mediterranean coast of the region of Valencia, Spain: 26 striped dolphins (Stenel/a coeruleoalba), 3 bottlenose dolphins (Tursiops truncatus) and 8 undetermined. The annual mortality rate in this territory has been 28.4 dolphins per year over the last 20 years. Therefore, an unusual episode of mortality should be considered. Because of the poor conservation code, only thirteen animals could be necropsied, revealing a high frequency of pneumonia, proven on microscopic examination as bronchointerstitial and non-suppurative, with atelectasic lung areas and enlarged/congestive lymph nodes. Three animals presented non-suppurative encephalitis with astrocytes containing characteristic viral inclusion bodies in two. Of all individuals tested for cetacean morbillivirus (CeMV) using a novel RT-PCR technique based on amplification of a 192-bp conserved region of the gene for the viral fusion protein, seven proved positive. Viremia was suggested because in five of the seven positive animals, CeMV was detected in at least two tissues. Phylogenetic analysis based on partía! sequencing of the phosphoprotein gene revealed a viral strain closely related to the dolphin morbillivirus (DMV) isolated in the mobillivirus epizootic of 2007. Therefore, given the nature of the lung and brain lesions and the detection of morbillivirus with high frequency, infection by DMV appears the cause for this new peak of strandings.