The influenza family likely traces its roots to life in the sea, according to researchers who mined genetic databases for clues. Scientists propose that these viruses first appeared in simple marine organisms hundreds of millions of years ago, long before modern fish evolved. The aquatic origins frame the influenza group as a robust set of viruses able to jump between hosts, a trait that could help explain how new human outbreaks begin. In the study, Mary Petrone, a virologist associated with Australian research institutions, notes that cross-host jumps are a hallmark of this viral family and that identifying these transitions can flag viruses with outbreak potential in people.
History often begins with a search for patterns. Petrone has built a career tracing the ancestral pathways of viruses, including a period that focused on SARS-CoV-2. When she shifted to fieldwork in Australia, she sought out one of the country’s most celebrated ecosystems—a coral reef—believing it could illuminate the deep past of animal viruses, especially those with RNA genomes. Corals belong to a lineage known as cnidaria, which diverged from other animals around 600 million years ago. The project aimed to uncover how ancient viral lineages relate to the viruses that now circulate among animals, including those capable of infecting humans and animals alike.
The research team began by connecting with coral scientists and collecting samples from species off Western Australia. RNA analysis from corals provided evidence of viral infections within a group that includes the influenza family and another cluster known as quarantine viruses. Some members of this second group move with ticks and occasionally reach humans, birds, and other vertebrates, underscoring the complexity of viral spread across environments.
The studies suggest that corals harbor viruses that are part of a family originating about 600 million years ago, with later branching giving rise to viruses that infect a broad array of hosts, including those closely related to humans. This implies that the flu and related viruses share ancient roots with other aquatic pathogens, a finding that reframes how researchers view the evolution of these infections.
In a separate line of inquiry, Petrone wondered whether flu-like viruses could have originated at sea. Earlier work had already hinted at this possibility, including the identification of a distant flu relative in a porpoise. Porpoises are small, slender marine mammals with a long evolutionary history, and researchers suggested that the influenza lineage co-evolved with early vertebrates.
Further clues emerged from genetic database analyses. Sequences related to flu-like RNA appeared in samples from Siberian sturgeon, a jawed fish closer to humans on the evolutionary tree than hagfish. Yet the sturgeon-derived virus diverged from the main flu family before other known influenza strains, including the hagfish virus, placing aquatic hosts at the center of the story of viral diversification.
Experts note that the earliest influenza strains probably infected aquatic animals before some made the leap to land-dwelling hosts. Still, it remains uncertain whether the move to terrestrial vertebrates occurred before other branches or happened more recently. To resolve this, scientists emphasize the need to uncover flu relatives across a broader range of animals and to map how the virus spreads from one host to another.
Origin in the oceans
Researchers from Shanghai and elsewhere have added weight to the sea-origin hypothesis. Ancestral analyses of deep-sea organisms revealed flu-related viruses in organisms like lobsters, pointing to a wide and largely untapped aquatic viral diversity. Experts say it would be surprising to find a substantial family of influenza viruses lacking an aquatic footprint, given the ancient and connected nature of marine life. The new work argues that influenza viruses may indeed have begun their journey in oceans before branching out to other environments.
Understanding historical host jumps is crucial for assessing current human risk. Signs of switching between crustaceans and other animals appear in the data, suggesting a pattern in which tick-associated viruses could move into new hosts after circulating in aquatic creatures. Such jumps illuminate how the zoonotic potential of viruses develops over time, offering a clearer view of how epidemics might arise when viruses alter their host range.
Experts caution that drawing firm conclusions about old host shifts must wait for more comprehensive sampling and a fuller family tree. Still, these studies contribute to a growing view that the influenza group and its kin formed a web of ancient relationships across the animal and marine worlds, a web whose strands may still influence present-day outbreaks in humans and wildlife.
In this effort, researchers emphasize that continued discovery in aquatic environments will be essential. The work aligns with broader efforts to map the history of viral emergence and to understand how viruses adapt to new hosts, a line of inquiry that is central to preparing for future public health challenges.
Overall, the research highlights the idea that the flu and its relatives trace their origins deep in the sea, with later stages of evolution linking aquatic and terrestrial life. As scientists gather more data from diverse species, the story will become clearer, revealing how these viruses moved through time and across habitats to shape the risk landscape for humans today.