Epidemiological analysis of Morbillivirus in cetaceans in the Canary Archipelago

Abstract

From 1999 to 2023, 30 cetaceans of various species stranded on the coasts of the Canary Islands exhibited microscopic lesions compatible with Cetacean morbillivirus (CeMV) infection, confirmed through immunohistochemical and/or molecular techniques. This study aimed to analyze prevalence and compare findings with other regions, assess temporal distribution, seasonal incidence, species affected, age-group susceptibility, disease presentation, and strain diversity. As a result, the prevalence of CeMV-positive cetaceans stranded on the Canary Islands coast during this period was 3.56%, which is relatively low compared to similar studies in other regions. CeMV infection cases were recorded in most years of the study period, with notable exceptions in 1999-2001, 2003- 2004, 2014, 2017, and 2023. Some of these periods were associated with outbreaks in the close Mediterranean Sea. A higher incidence of CeMV was observed during the spring and winter seasons, with 30% and 27% of CeMV-positive strandings occurring during these periods, respectively. Eight different cetacean species were infected by CeMV during the study period in the Canary Islands. The short-finned pilot whale (Globicephala macrorhynchus) and the striped dolphin (Stenella coeruleoalba) had the highest number of positive cases. An age susceptibility was noticed, since juveniles or subadults comprised the majority (63%) of CeMV-infected animals that stranded. Despite no reported outbreaks, most CeMV-infected cetaceans in the Canary Islands presented with the acute systemic form of the disease, predominantly affecting striped dolphins. Two distinct strains of CeMV circulate in Canary Islands waters: DMV is widespread among various cetacean species, while PWMV has been associated with an unusual mortality event and chronic localized encephalitis in short-finned pilot whales. These findings provide insights into the prevalence, seasonal patterns, species susceptibility, and strain diversity of CeMV in the Canary Islands over a 25-year study period.