Scientists have discovered a "distant cousin" of the Covid-19 virus in a treasured New Zealand freshwater fish - but they stress there's no risk to people.
Coronaviruses are a diverse family comprising hundreds of different types, of which just a few - the common cold and the Sars-CoV-19 virus among them - can affect humans.
While coronaviruses are generally more associated with mammals and birds, they've also been known to infect fish and other marine species.
In lamprey, or kanakana/piharau, Kiwi scientists have just revealed a new type of coronavirus which they suspect has been infecting fish species for millions of years.
Southland-based ecologist Dr Jane Kitson, who co-authored a new study reporting the findings, said kanakana/piharau have been in the fossil record for more than 360 million years.
"They are a culturally important taonga species and are mahinga kai (gathered food) for Māori," Kitson said.
"If you've seen a kanakana/piharau in your local stream, you are lucky. They are a secretive fish and like to hide under rocks or in silty-sandy riverbeds."
Currently, its populations are in decline and they're classified as threatened/nationally vulnerable by the Department of Conservation.
Among other threats, the species face a disease called lamprey reddening syndrome, or LRS, causing haemorrhaging underneath the fish's skin.
"The disease can kill the fish and its cause is as yet unknown," said co-author Dr Cindy Baker, a freshwater fish scientist at Niwa.
While studying a small number of lamprey infected with LRS, a meta-transcriptomic analysis revealed the fish were also carrying the undocumented coronavirus, tentatively named Kanakana letovirus.
The discovery prompted scientists to look for coronaviruses in other fish species in Australia and elsewhere.
Another new type has since been found in carp in Australia's Murray-Darling Basin.
As for kanakana/piharau, it wasn't yet clear whether there was a link between LRS and the new coronavirus.
Researchers are now trying to find a connection - which isn't an easy task.
Studies have shown how fish carry an enormous diversity of viruses - the majority of which appeared to cause asymptomatic infections.
"The new coronavirus has probably been infecting fish species for hundreds of millions of years," said the paper's first author, Allison Miller, who carried out the project as an Otago University PhD student.
"This study suggests that this virus might have jumped to kanakana/piharau from other fish species; however, when or where this jump might have occurred is unknown – it could have been many millions of years ago."
Scientists have long known coronaviruses can leap between species.
Leaps between species were especially frequent in virus families in which genetic material was encoded in RNA rather than DNA - such as coronaviruses like Sars-CoV-2 and closely-related Sars and Mers.
"However, these host-jumps usually occur between closely related hosts, for example between mammals," Otago University and ESR virologist Dr Jemma Geoghegan said.
"Importantly, due to the major differences in the virus and its host biology, this virus poses no risk for jumping into humans."
Geoghegan hoped to gain a better understanding of host-jumping from a just-launched project exploring viruses within New Zealand's native and introduced species.
Viruses, more broadly, are the most abundant biological entities on Earth - more than a quadrillion-quadrillion individual ones are thought to exist, and the bulk of them remain undescribed.