In a groundbreaking discovery, scientists have uncovered two previously unidentified viruses in short-finned pilot whales and orcas inhabiting the Caribbean region of the North Atlantic Ocean. This remarkable research, which brings together students and experienced researchers from institutions such as Arizona State University (ASU), Coastal Carolina University, and The University of the South in the United States, also includes contributors from Saint Vincent and the Grenadines, The University of the West Indies at Cave Hill in Barbados, the University of Cape Town in South Africa, and the prestigious Institut Pasteur in France. Notably, this discovery marks the first incidence of circoviruses being found in cetaceans within this geographical area, further expanding our understanding of viruses that can infect marine vertebrates.
The study, aptly titled "Novel circoviruses identified in short-finned pilot whale and orca from the North Atlantic Ocean," is spearheaded by Arvind Varsani, a virologist affiliated with ASU’s School of Life Sciences and Biodesign Institute, with Matthew De Koch serving as the lead author. Utilizing high-throughput genetic sequencing, the research team meticulously analyzed archived tissue samples collected from deceased whales. These samples were obtained through long-standing collaborative efforts between Russell Fielding from Coastal Carolina University and local subsistence whalers on the island of St. Vincent.
Through their rigorous analysis, the researchers successfully retrieved seven complete genomes of circoviruses. Among these, five genomes were sourced from short-finned pilot whales, while two were identified in orcas. These newly discovered viruses represent two entirely novel species, which the researchers have designated as shofin circovirus and orcin circovirus. Both of these new species are distinct from the only other known cetacean circovirus, the beaked whale circovirus, which had been previously documented in a stranded whale located in the Pacific Ocean.
What sets these viruses apart is particularly intriguing. The research delved into the structure of the viruses' capsid proteins, which constitute the protective outer layer. Unusually large surface-exposed loops were identified, most notably the E-F loop, which is nearly double the length of the corresponding structure found in porcine circovirus 2, one of the most comprehensively studied circoviruses. Additionally, genetic assessments indicated that the circoviruses detected in whales and other cetaceans form a distinct monophyletic group within the Circovirus genus, showcasing a clear evolutionary relationship.
According to the limited data currently available, the study posits that circoviruses may have been infecting the ancestors of modern cetaceans quite early in their evolutionary journey. However, the authors emphasize the necessity for more extensive genetic data across a broader spectrum of species to adequately explore and validate this hypothesis.
Yet, several critical questions remain unanswered regarding the health implications and transmission methods of these circoviruses. The researchers reference earlier findings related to beaked whale circovirus, which hinted at a potential link to immunosuppression. This finding mirrors how circoviruses impact certain terrestrial mammals and avian species. Nonetheless, the authors underscore the importance of conducting further research to gain a deeper understanding of the diversity of circoviruses in cetaceans, the modes of their transmission, and the potential health effects they may pose to both whales and orcas.
