Not that the pandemic-anxious need anything to add to their arsenal of anxiety sources, but the New York Times has a story today about an ongoing mystery happening in wastewater surveillance of COVID-19 that researchers can't pin down.

In particular "sewersheds" in New York City, which have not been publicly identified, researchers continue to find "cryptic lineages" of the COVID virus as they genetically sequence viral fragments found in wastewater — bits of the virus that show a "unique constellation of mutations" not seen in any known variant. And these mutations have been observed going back at least a year, without any known case of a similar variant from this lineage every having been found in a human subject.

As the Times reports, via this new study published today in Nature Communications, the finding are unsettling because they suggest the potential for even more advanced and mutated COVID variants that could evade existing vaccines and antibodies. And, the study notes, many of these lineages "share many mutations with the Omicron variant of concern," and yet they are unknown in existing databases — and if they have passed through human hosts, they most likely would have been detected at some point.

Researchers at UC Berkeley, who have been monitoring wastewater from multiple sewersheds around the Bay Area (and perhaps further afield in California) since the middle of 2020, say they've found similar "cryptic lineages" here as well. Rose Kantor, a microbiologist at Berkeley, confirmed this with the Times, though the location of the findings was not disclosed.

The New York samples of these mystery lineages all come from particular parts of the city, and a researcher there, Dr. John Dennehy of Queens College, tells the Times, "We were able to pin it down to a very small area of the sewershed."

Still, Dennehy says they can't pin it down any further, and researchers disagree about whether these bits of virus are coming from human or perhaps animal hosts. One theory is that the virus could be mutating in rodents in one particular area — and New York has a sizable rat population.

Adding to the non-human arguments, these cryptic lineages made up a larger percentage of the viral samples found in wastewater last May and June, when COVID cases were at a pandemic low among humans in New York.

As one researcher in the project, University of Missouri virologist Marc Johnson, tells the Times, "This is a very promiscuous virus. It can infect all kinds of species."

Still, Dr. Johnson says "none of it makes perfect sense" when it comes to the evidence they have so far — like, if the virus is mutating in rats, how did rats get it from humans in the first place? Also, the researchers have been trying to identify the lineages in live rats, but they've come up short there so far, and it could be that there's another animal species they're missing. Housecats? Dogs?

Theories continue to hold sway about Omicron, and the idea that it might have mutated in animal hosts somewhere before crossing back into humans. So ideas that COVID continues to get weirder and potentially more infectious, somewhere, in some species, if not yet in humans, is... concerning!

Related: Health Officials Say Don't Worry, But There's a New Omicron Subvariant In the Bay Area

Image: Omicron rendering via Getty Images