Wastewater testing finds H5N1 avian flu in 9 Texas cities

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Researchers who sequenced viruses from wastewater samples from 10 Texas cities found H5N1 avian flu virus in 9 of them, sometimes at levels that rivaled seasonal flu.

In other developments, the Centers for Disease Control and Prevention (CDC) in updates on its response to H5N1 outbreaks in cattle said experiments in ferrets began last week.

Findings tilt toward animal source 

A team from Baylor College of Medicine and the University of Texas Health Sciences Center detailed their whole-virome sequencing findings in a new preprint study.

With many questions still unanswered about how the virus is spreading in dairy cows and how widely the virus is circulating, scientists are increasingly eyeing wastewater sampling as a key surveillance tool.

The group reported H5N1 in wastewater from March 4 to April 25. They said 19 of 23 monitored wastewater sites had at least one detection event and that, over time, H5N1 became the dominant serotype. They did not name the 10 cities they monitored, and the findings have yet to be peer-reviewed. 

On X, Mike Tisza, PhD, the first author of the study and assistant professor of virology and microbiology at Baylor, said it's still not clear where the viruses came from, but the evidence tilts toward an animal source, because the researchers didn't see any mutations with known links to human adaptation.

He added that the network in Texas appears to be the only one using the wastewater sequencing technology, but that H5N1 is probably present in wastewater in other areas. If the virus becomes more of a problem, Tisza said wastewater sequencing may be the best way to identify new adaptive mutations. 

CDC launches ferret experiments

In a May 10 response update, the CDC said more than 260 people have so far been monitored for H5N1 symptoms following exposure to infected or potentially infected animals. Of at least 33 who had flulike symptoms, no additional human cases have been reported beyond an initial case in a Texas dairy worker who had conjunctivitis.

The CDC said it is still in talks with multiple states about state-led field epidemiologic investigations.

Meanwhile, the group said it is moving ahead with scientific work to better characterize the virus, Last week it experimentally infected ferrets with the virus that infected the Texas dairy worker to assess disease severity and transmission under different contact scenarios. Scientists often use ferrets as a model to assess flu viruses because they get sick and transmit them similar to people.

Results are expected in about 3 weeks, and the CDC said experimental infection of various cell lines will follow.

In other developments:

• The US Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) reported more outbreaks in poultry in three states, including two that have reported H5N1 in dairy herds. Idaho reported two more poultry outbreaks, both in Jerome County. One occurred at a farm housing 1,000 birds and the other struck a backyard location that has 20 birds. Michigan reported another outbreak in Ionia County, which affected a backyard flock. And California reported a detection at a live-bird market in San Francisco.
• An animal influenza expert group of the World Organization for Animal Health and the UN Food and Agriculture Organization, known as OFFLU, today issued a statement on H5N1 in dairy cows, noting that the B3.13 genotype hadn't been detected in poultry before it turned up in cattle. Before November 2023, it had been seen in only a few wild birds and one skunk. So far, B3.13 hasn't been detected outside of the United States, but the group said it continues to monitor the situation.