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Influenza A virus found in wastewater samples from 59 sewage systems this spring is the same strain of influenza A virus that currently infects dairy cattle.
So far, the US Department of Agriculture has reported that more than 30 dairy cows have been infected with H5N1 influenza in nine states. But there are questions about the extent of the outbreak and whether the US can adequately monitor it.
USDA officials acknowledged in a press release last week that getting milk producers to test for infections is difficult. Recently, the milk purchased at the grocery store tested positive for HIV 1 out of 5 samples were testedAlthough further testing showed that virus fragments found in milk were not infectious.
Last week, at a multi-agency news conference on the government's response to the pandemic, Dr. Nirav Shah, deputy director of the US Centers for Disease Control and Prevention, said the agency was looking into whether it could be used. Waste water to identify areas where the virus spreads. First, he said, scientists need to develop a test to distinguish between H5 influenza and A-strain flu viruses.
Scientists at Emory, Stanford and Verley Life Sciences, a research organization now affiliated with the WastewaterSCAN network that monitors large wastewater treatment plants across the US, say they did.
Wastewater testing is an inconvenient way to monitor the spread of infections. Washing to test for pathogens does not depend on humans or animals. Instead, evidence enters the wastewater every time a toilet is flushed or someone flushes the material down the drain.
Of the 190 wastewater treatment plants currently monitoring sludge samples for influenza A, 59 A-strain viruses spiked this spring, just as human flu cases leveled off or fell. Wastewater experts thought it might be H5N1 avian influenza infections, which are highly pathogenic in dairy cattle or other animals.
The WastewaterSCAN team developed a test to test for the flu virus H5 gene and used it on samples collected from sewage systems near Texas where dairy cattle have tested positive, but not directly involving sewage from farms.
The team measured genetic markers specific to both influenza A viruses and H5 viruses.
When the indicators of influenza A viruses began to increase in early March, the indicators of H5 viruses began to increase continuously. The concentration of the H5 gene in the samples was generally higher than that of influenza A viruses, suggesting that a large proportion of the viruses in the samples were H5N1.
What's more, the amount of influenza A virus measured in sewage sludge samples taken from the Amarillo, Texas area was “one of the highest ever measured in wastewater,” according to the study.
The accumulated sludge samples tested for the study were taken between February 4 and April 16 at two treatment plants in the Amarillo City watershed and a third wastewater treatment plant in Dallas County. The researchers found that wastewater treatment plants sampled in the Amarillo area allowed some producers to dispose of animal by-products, including discarded milk from dairies, which explains the high levels of influenza A viruses and H5 viruses found in their samples.
Researchers say their study could be an early warning for bird flu in farm animals, just as previous wastewater tests have shown a rise in the number of Covid-19 infections.
“We found the H5 signal before the presence of highly pathogenic avian influenza in these counties,” said Dr. Alexandria Boehm, a professor of civil and environmental engineering at Stanford University.
“I think that's very interesting. “This means that the wastewater in this particular situation, with this particular pathogen, could reveal information about what's going on in these cattle before it's publicly available,” Boehm said.
It was the paper. Posted as a pre-print on the BioArchives server before rigorous review by external experts. The researchers said they are working to have it published in a scientific journal.
No HIV was found in the cows in the sewage they tested. Instead, they think the legal dumping of milk caused the spike in H5 virus that they saw in early March.
The researchers said they could not rule out that all of the H5 genetic material they collected in the wastewater came from dairy cattle. It can be from birds or even from people.
The researchers also say they don't have enough data to know where the increase in influenza A virus is coming from in different states.
“We do not know the answer to this question. It's something that I think needs to be monitored,” Boehm said.
But if the increase in viruses comes from milk or other animal waste dumped in controlled sewers – and this is still very large – this means that the epidemic is much more widespread than currently known.
“If dairy industry operations in these sewers are a major source of H5 in the wastewater, this suggests that milk from infected animals needs to be removed from the food supply, suggesting the possibility of additional and unknown outbreaks of dairy cattle being sent to these facilities,” the study authors commented.
But the researchers say their results should be interpreted with caution. The source of the virus cannot be confirmed without monitoring possible sources in the controlled drains.
“However, several lines of evidence point to animal sources,” the paper says.
The researchers say that their test method is very sensitive. It can detect genetic material from even small amounts of H5 viruses, but it cannot tell if the viruses can infect people and make them sick. Bohm said they didn't try to culture them to see if the virus could infect cells.
The United States Food and Drug Administration announced last week that it had been testing samples of pasteurized milk that showed signs of the H5N1 virus and so far said the milk was not contagious and could not make people sick.
Waste water The researchers acknowledge that they may be picking up other H5 viruses in their tests, including the less pathogenic H5 influenza viruses.
“It's a situation where we feel ethically bound to share this information with our colleagues in pre-publication and start the conversation, because there are very important unanswered questions to answer,” Boehm said.