New circoviruses discovered in pilot whales and orcas from the North Atlantic 

(Press-News.org) A collaborative team of researchers (that includes students and senior researchers at Arizona State University (ASU), Coastal Carolina University, The University of the South in the US and researchers in Saint Vincent and the Grenadines, The University of the West Indies at Cave Hill (Barbados), University of Cape Town (South Africa), Institut Pasteur (France) have identified two previously unknown circoviruses in short-finned pilot whales and orcas from the Caribbean region of the North Atlantic Ocean. The findings represent the first detection of cetacean circoviruses in this region and expand the known diversity of circoviruses in marine vertebrates.   

The study, titled, “Novel circoviruses identified in short-finned pilot whale and orca from the North Atlantic Ocean” with first author Matthew De Koch, was led by ASU’s School of Life Sciences and Biodesign Institute virologist Arvind Varsani, and used high-throughput sequencing to screen archived tissue samples collected from deceased whales through long-standing collaborations between Russell Fielding (Coastal Carolina University) and artisanal subsistence whalers on the island of St. Vincent. Seven complete circovirus genomes were recovered. Five came from short-finned pilot whales and two from orcas. These viruses represent two novel species, named shofin circovirus and orcin circovirus.  Both viruses are also distinct from the only previously known cetacean circovirus, beaked whale circovirus, which was identified from a stranded whale in the Pacific.   

Analysis of the capsid proteins revealed notable elaborations in the surface-exposed loops (particularly the E-F loop), which is nearly twice as long as that of well-studied porcine circovirus 2. Cetacean circoviruses form a distinct, well-supported monophyletic clade within the genus Circovirus. The study notes that the limited available data support the possibility that circoviruses may have been infecting cetacean ancestors early in their evolutionary history, although additional sequence data across more taxa are needed to assess this hypothesis.   

The transmission routes and disease impacts of circoviruses in cetaceans remain unknown. The manuscript cites previous work on beaked whale circovirus that suggested immunosuppression, consistent with known effects of circoviruses in terrestrial mammals and birds, but the authors emphasize the need for further research on circovirus diversity, transmission and pathogenicity in cetaceans.   

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