There is no evidence that the lineages, which have been circulating for
at least a year without overtaking Delta or Omicron, pose an elevated
health risk to humans. But the researchers, whose findings
in Nature Communications on Thursday, still have no idea
where they came from.
“At this point, what we can say is that we haven’t found the cryptic
lineages in human databases, and we have looked all over,
” said
Monica Trujillo, a microbiologist at Queensborough Community
College and an author of the new paper.
The researchers themselves are torn about the lineages’ origins. Some
lean toward the explanation that the virus is coming from people
whose infections aren’t being captured by sequencing. But others
suspect that the lineages may be coming from virus-infected animals,
possibly the city’s enormous population of rats. Even then, the favored
theory can change from day-to-day or hour-to-hour.
Answers remain elusive.
In New York City Sewage, a Mysterious Coronavirus Signal
https://getpocket.com/read/3543635796 3/8
“I think it’s really important that we find the source, and we have not
been able to pin that down,
” said John Dennehy, a virologist at Queens
College and an author of the paper.
ed wastewater samples, colored black because of the binding agent that adheres to coronavirus particles, in John Dennehy’
eens College.Credit...Jackie Molloy for The New York Times
Strange sequences
The researchers — who also include Marc Johnson, a virologist at the
University of Missouri, Davida Smyth, a microbiologist at Texas A&M
University and others — have been sampling wastewater from 14
treatment plants in New York City since June 2020. In January of 2021,
they began doing targeted sequencing of the samples, focusing on part
of the gene for the virus’s all-important spike protein.
Although this approach provides a limited look at the viral genome, it
allows researchers to extract a lot of data from wastewater, in which
the virus is typically fragmented.
Viral fragments with novel patterns of mutations appeared repeatedly
at a handful of treatment plants, the researchers found. (They could
not disclose the specific plants or areas of the city, they said.)
“To date we have not seen these variants among clinical patients in
N.Y.C.,
” said Michael Lanza, a spokesman for New York City
Department of Health and Mental Hygiene.
2/3/2022 Pocket - In New York City Sewage, a Mysterious Coronavirus Signal
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Researchers at the University of California at Berkeley have found
similar sequences in one California sewershed, said Rose Kantor, a
microbiologist at the university.
ennehy speculated that the “cryptic lineages” could be coming from people who are confined to long-term health care facil
e has been unable to prove it.Credit...Jackie Molloy for The New York Times
The scientists’ continuing quest to figure out where the sequences are
coming from highlights both the potential of wastewater surveillance,
which can help scientists keep tabs on how the virus is evolving, and
the challenge of making sense of any anomalies pulled out of the
murk.
“We really struggled trying to understand what it was that we had,
” Dr.
Trujillo said.
The lineages could be coming from people whose infections have
escaped detection or whose virus has not been sequenced.
But the fact that they kept turning up at the same few wastewater
plants makes this theory less likely, the researchers said, given that
New Yorkers, and any variants they may be carrying, tend to move
throughout the city without restriction.
Still, Dr. Dennehy speculated that the sequences could be coming
from people who are confined to long-term health care facilities in just
a few areas of the city. But he has not been able to prove it.
2/3/2022 Pocket - In New York City Sewage, a Mysterious Coronavirus Signal
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“We were able to pin it down to a very small area of the sewershed,
”
Dr. Dennehy said. “And I emailed doctors and hospitals in those areas
and never once got a response to my emails.”
Indeed, people who have compromised immune systems may have
more difficulty fighting off the virus, giving it more opportunities to
mutate. Many scientists theorize that Omicron emerged from an
immunocompromised patient.
Intriguingly, some of the cryptic lineages have some of the same
mutations as Omicron, or mutations in the same locations. Laboratory
experiments suggest that these lineages may also be able to evade
some antibodies.
The New York City lineages might be a result of the same kind of
selective pressure to evade some of the body’s immune defenses, the
researchers theorize.
Johnson, a virologist at the University of Missouri, loaded wastewater samples into a centrifuge. “This is a very promiscuo
” he said. “It can infect all kinds of species.”Credit...Michael B. Thomas for The New York Times
On the other hand, the lineages have been circulating for long enough
now that they should have appeared in at least one sample sequenced
from an infected person, some scientists said.
“To have something in a sewershed that you’re detecting, you need a
fair bit of it around,
” said Dr. Adam Lauring, a virologist at the
University of Michigan, who was not involved in the research.
2/3/2022 Pocket - In New York City Sewage, a Mysterious Coronavirus Signal
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Dr. Johnson, the Missouri virologist, agrees. He favors the hypothesis
that the sequences are coming from animals, perhaps a few specific
populations with limited territories. In May and June of 2021, when
the number of human Covid-19 cases in the city was low, the
mysterious lineages made up a greater proportion of the viral RNA in
wastewater, suggesting that they may have come from a nonhuman
source.
The researchers initially considered a diverse array of potential hosts,
from squirrels to skunks. “This is a very promiscuous virus,
” Dr.
Johnson said. “It can infect all kinds of species.”
To narrow down the possibilities, they went back to the wastewater,
assuming that any animal that was shedding virus might be leaving its
own genetic material behind, too.
Although a vast majority of the genetic material in the water came
from humans, small amounts of RNA from dogs, cats and rats were
also present, the scientists found.
Dr. Johnson has been considering rats, which roam the city by the
millions. In his lab, he created pseudoviruses — harmless,
nonreplicating viruses — with the same mutations present in the
cryptic sequences. The pseudoviruses were able to infect both mouse
and rat cells, he found. The original version of the virus does not
appear able to infect rodents, although some other variants, like Beta,
can.
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“So in and of itself, that isn’t huge data, but it is at least consistent with
the idea that it’s coming from rodents,
” Dr. Johnson said.
Since last summer, the scientists have been working with Animal and
Plant Health Inspection Service at the U.S. Department of Agriculture
to look for signs of the virus in blood and fecal samples from local rats.
So far, they’ve come up empty.
“Maybe we’re not hitting the right animals,
” Dr. Dennehy said.
Or maybe rats aren’t the source of the mystery lineages. Scientists
have repeatedly found that human can pass the virus to animals,
especially pets, zoo animals, farmed mink and others with which they
are in frequent contact. That has raised concerns that the virus might
establish itself in an animal reservoir, where it might mutate and get
passed back to humans.
But rats have not typically been high on the list of concern, and there
has not been any evidence that the virus is circulating in wild rats. The
pathway by which humans could have infected rats is also unknown.
“Nothing makes perfect sense,
” Dr. Johnson said.
But some kind of animal origin remains a possibility, scientists said.
“It’s just as plausible, if not more plausible, than a human origin,
” Dr.
Lauring said.
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Printed with ❤️ from Pocket
So the search continues. Dr. Johnson has developed a new technique
that can amplify only non-Omicron sequences, which should make it
easier to detect the lineages. He has also begun searching for similar
lineages in sewage samples from other states, which might help
provide further clues to their origins.
“We will know eventually,
” Dr. Johnson said."
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