Genetics to determine the aquatic origin of influenza
Corals, sea urchins and other aquatic creatures show signs of disease infection
The virus could start in the fish. Researchers combing through genetic databases have discovered a distant relative of the influenza virus responsible for the seasonal flu, not to mention a fluvial fluvial group: the acipenser.
The authors also found that the broader family of viruses that includes influenza probably arose 100 million years ago in primitive aquatic animals, long before the first fish.
Viruses in this group seem particularly adept at jumping around between groups, says Mary Petrone, a virologist at the University of Sydney, Australia, who co-authored a preliminary report on the findings. Knowing once the host jumps can help scientists identify viruses with the potential to trigger new human epidemics.
History of the origin of the flu
Like many virologists, Petrone spent the first two years of the pandemic intensively studying SARS-CoV-2. But when he moved to Australia to do postdoctoral research, Petrone wanted to avoid human contamination and spend time in one of the country’s most famous ecosystems. “After two years of working on Covid, I thought it would be really good to do coral reefs in the field,” he said.
A group of corals is called the phylum Cnidaria, whose ancestors branched off from other animals about 600 million years ago. Petrone hoped that the corals he studied could have a deeper history of viruses that infect animals, especially those with RNA genomes. This group of viruses includes many human and animal pathogens.
Petron’s first call was not to a dive shop, but to Zoe Richards, a coral researcher at Curtin University in Bentley, Australia, who collected samples of two species of coral off the coast of Western Australia. Analysis of RNA collected from corals provides evidence of infection with viruses belonging to the Articulaviridae collection, which includes the influenza virus family and a group called Quaranjaviruses. Members of the latter group work on ticks and sometimes sneak up on humans, birds, and other vertebrates.
The new analysis suggests that the coral-infecting virus is part of an ancient viral family that likely arose around 600 million years ago, after which other members of the articulaviral family, influenza and Quaranjaviruses, arose.
Hagfish Secrets
Right image: A human cell (artificially colored) infected with the influenza virus, which may have originated in fish before moving to land animals.
The discovery left Petrone wondering if the virus could even be born in the sea. Now some evidence. In 2018, researchers identified a distant relative of the flu in the agape. These slimy, jaw-dropping creatures evolved from an early vertebrate lineage, and the authors’ study suggested that disease evolved from the vertebrate side.
Searching genetic databases, Petrone found flu-RNA sequences in samples of the Siberian sturgeon (Acipenser Baerii). Sturgeons are jawed vertebrates, closer to humans than to fish. But the sturgeon virus spread from the main family tree before any other known flu virus, including the hagfish virus.
The discovery of two early rivers suggests the disease likely infected aquatic animals, including fish, before moving to land, Petrone says. But it is not clear whether the river moved to land with the first terrestrial vertebrates, or whether it jumped from the sea to land more recently.
To determine this, researchers will need to look for related diseases in more animals and gain a better understanding of how the virus spreads between host species, the researchers say.
born in the sea
Jie Cui, an evolutionary virologist at the Shanghai Pasteur Institute in China, agrees that the disease and its wider family originated from the sea. In 2021, his team deeply analyzed the genomes of marine lobsters and identified a virus that is part of a wider group 3 flu. “There is a lot of viral variation in aquatic environments,” he said.
Robert Gifford, an evolutionary virologist at the University of Glasgow, UK, says it is surprising to find a greater number of viruses that did not originate in aquatic environments because of the ancient nature of marine life. “The study provides clear evidence that the influenza virus has an aquatic origin.”
Identifying ancient hosts could also help researchers assess the risk that certain viruses pose to humans, the researchers say. Petrian’s team found signs that tick-infecting quaranjaviruses may have jumped to the creatures after first getting around in crustaceans.
Discovering such jumps shows that the study of aquatic viruses “helps us better understand the historical emergence and evolution of zoonotic potential viruses,” adds Chantal Vogels, an arbovirologist at Yale School of Public Health in Newport, Connecticut.
Gifford agrees that studies like Petrini’s could help identify viruses that have the potential to cause epidemics in humans and other animals. But he cautions that conclusions about jumps may change the old host, so that more of the viral family tree is filled in with reshuffled relationships.
The study was published on February 16 to the Biorxiv preprint server and has not yet been reviewed: Evidence for the origin of aquatic influenza viruses and the order articulavirals
