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 murkwe really struggled trying to understand what it was that we had dr trujillo saidthe lineages could be coming from people whose infections have escaped detection or whose virus has not been sequencedbut 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 restrictionstill dr dennehy speculated that the sequences could be coming from people who are confined to longterm health care facilities in just a few areas of the city but he has not been able to prove itwe 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 emailsindeed 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 patientintriguingly 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 antibodiesthe new york city lineages might be a result of the same kind of selective pressure to evade some of the bodys immune defenses the researchers theorizean animal originimagecreditmichael b thomas for the new york timeson 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 saidto have something in a sewershed that youre 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 researchdr 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 covid19 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 sourcethe 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 speciesto 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 tooalthough 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 founddr johnson has been considering rats which roam the city by the millions