Whales and orcas were carrying viruses no one knew existed

The findings come from a study titled "Novel circoviruses identified in short-finned pilot whale and orca from the North Atlantic Ocean," led by Arvind Varsani, a virologist at ASU's School of Life Sciences and Biodesign Institute. The study's first author is Matthew De Koch. Researchers used high-throughput genetic sequencing to analyze archived tissue samples taken from deceased whales. These samples were collected through long-standing collaborations between Russell Fielding (Coastal Carolina University) and artisanal subsistence whalers on the island of St. Vincent.

From this analysis, scientists recovered seven complete circovirus genomes. Five of the genomes came from short-finned pilot whales, while two were found in orcas. The viruses represent two entirely new species, which the researchers named shofin circovirus and orcin circovirus. Both are clearly different from the only cetacean circovirus previously known, beaked whale circovirus, which was identified earlier in a stranded whale from the Pacific Ocean.

What Makes These Viruses Distinct

Further examination focused on the viruses' capsid proteins, which form the outer shell of the virus. The researchers found unusually large surface-exposed loops, especially the E-F loop. This region is nearly twice as long as the same structure in porcine circovirus 2, one of the most extensively studied circoviruses. Genetic analysis also showed that circoviruses found in whales and other cetaceans form a distinct and well-supported monophyletic group within the genus Circovirus.

Based on the limited data currently available, the study suggests that circoviruses may have been infecting the ancestors of modern cetaceans early in their evolutionary history. However, the authors caution that more genetic data from a wider range of species are needed to properly test this idea.

Unanswered Questions About Health and Transmission

How these circoviruses spread among whales and whether they cause disease remain open questions. The researchers point to earlier work on beaked whale circovirus that suggested a link to immunosuppression, a pattern that aligns with how circoviruses affect some land mammals and birds. Even so, the authors stress that much more research is required to understand the diversity of circoviruses in cetaceans, how they are transmitted, and what effects they may have on whale and orca health.