by Spikes of the influenza A virus seen in wastewater samples from 59 sewage systems across 18 different states this spring could indicate the spread of the H5N1 bird flu virus currently infecting dairy cattle, according to a new study .
So far, the US Department of Agriculture has reported that more than 30 dairy herds have been infected with H5N1 influenza across nine states. But there are questions about how big the outbreak could be and whether the US can adequately track it.
In a news conference last week, USDA officials acknowledged that it was difficult to get milk producers to allow them to be tested for the infection. Recent tests of milk purchased in grocery stores found genetic material from the H5N1 virus in 1 out of 5 samples tested, although further testing showed that the virus fragments detected in milk were not infectious.
Last week, in a multi-agency news conference on the government’s response to the spread of the virus, Dr. Nirav Shah, principal deputy director of the US Centers for Disease Control and Prevention, said the agency was looking into whether it could be use. wastewater to locate the areas where the virus is spreading. First, he said, scientists would have to develop a test that could distinguish H5 flu from the larger soup of circulating A-strain flu viruses.
Now scientists at Emory, Stanford and Verily Life Sciences, a research organization affiliated with the WastewaterSCAN network that monitors a large network of wastewater treatment plants across the US, say they have done just that.
Wastewater testing is a passive way to track the spread of infections. It does not require people or animals to be swabbed to test for pathogens. Instead, evidence flows into the wastewater every time a toilet is flushed or someone dumps material down a drain.
Of 190 wastewater treatment plants that currently monitor sludge samples for influenza A, A-strain viruses increased in 59 this spring, just as human influenza cases were flat or falling. Wastewater experts wondered if it could come from H5N1, the highly pathogenic bird flu infections in dairy cattle or other animals.
The WastewaterSCAN team developed a test to check for the H5 gene of the flu virus and used it on stored samples from sewage systems near areas in Texas where dairy cattle had tested positive, but excluding wastewater directly from the farms.
The team measured a genetic marker for influenza A viruses and genetic markers specific to H5 viruses.
As marker levels for influenza A viruses began to rise in early March, markers for the H5 virus began to rise in tandem. The concentration of the H5 gene in the samples was almost as high as the concentration of influenza A viruses overall, suggesting that a large proportion of the viruses in the samples were H5N1.
In addition, the concentration of influenza A viruses measured in these wastewater sludge samples from the Amarillo, Texas, area was “among the highest ever measured in wastewater,” the study noted.
The stored sludge samples tested for the study were taken between February 4 and April 16 at two treatment plant sites in the City of Amarillo watershed, and a third wastewater treatment plant in Dallas County. The researchers confirmed that wastewater processing plants sampled in the Amarillo area allowed some producers to dispose of animal byproducts, including dumped milk from dairies, which could explain the high concentrations of influenza A viruses, and H5 viruses in their samples.
Just as wastewater testing has proven to be a trigger for elevated Covid-19 infections in the past, researchers say their study suggests it could also be an early warning for bird flu outbreaks in farm animals.
“We detected the H5 marker just before highly pathogenic avian influenza was confirmed in those counties,” said Dr. Alexandria Boehm, who is a professor of civil and environmental engineering at Stanford University.
“I think it’s really interesting. It means that the wastewater in this particular case, with this particular pathogen, can reveal information about what was circulating in these cattle before information was publicly available,” said Boehm.
The paper was posted as a preprint on the BioRxiv server, before rigorous review by external experts. The researchers say they are working to publish it in a scientific journal.
The study authors emphasize that no H5N1 outbreaks in cows have been reported in any of the sewers they tested. Instead, they think the big spikes in the H5 virus they saw in early March were probably caused by milk dumping.
The researchers note that they cannot rule out that the H5 genetic material they are picking up in all the wastewater from dairy cattle. It could be from birds or even people.
The researchers say they also don’t have enough information to know where the increases in influenza A virus are coming from across multiple states.
“We don’t know the answer to that question. It’s something that I think needs to be followed up,” Boehm said.
But if the spike in viruses comes from dumped milk or other animal waste throughout the rooms they monitor – and that’s still quite large – it means the outbreak is likely to be much more widespread than known at the moment.
“If the activities of the dairy industry in these sewage sheds are the main source of H5 in wastewater, it suggests that there may be additional unrecognized outbreaks among dairy cattle sent to these facilities due to the need to divert milk from infected animals from the food supply,” note the study’s authors.
But the researchers also say their findings should be interpreted with caution. Without tracking down potential sources in the sewers they monitor, the source of the virus cannot be proven.
“However, multiple lines of evidence suggest animal sources,” the paper says.
The researchers say their test method is very sensitive. It can even detect small amounts of the genetic material from the H5 viruses, but they can’t tell if the viruses would be able to infect people and make them sick. Boehm says they didn’t try to grow the virus to see if it could infect cells.
The US Food and Drug Administration said last week that they are testing samples of pasteurized milk that have found traces of the H5N1 virus and so far have found that the milk is not contagious and cannot make people sick.
The wastewater researchers acknowledge that their tests may also be picking up other types of H5 viruses, including low-pathogenic H5 flu viruses, but say these are not expected to be circulating in these areas at this time.
“This is a case where we really felt ethically bound to share this information with colleagues through a preprint and move the conversation forward, because there are unanswered questions that are really important to answer,” Boehm said.
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