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A gene found in a strain of avian influenza – H5N1 – was detected in industrial discharge from the Forsyth County/ Winston-Salem wastewater treatment plant last month, scientists found, coinciding with an outbreak in a herd of dairy cattle in west-central North Carolina.
Scientists at Stanford and Emory universities published their findings May 20 in the peer-reviewed journal Environmental Science & Technology Letters. “It is the first study to suggest H5N1 is detectable in wastewater and provides evidence for potential sources,” the scientists wrote. “This work can aid in the response to the current avian influenza outbreak.”
The gene was also present in wastewater from two other treatment plants in Amarillo, Texas, and Dallas County, Texas, where dairy cattle were also sickened.
Forsyth County Public Health Director Joshua Swift told Newsline that the detection “does not mean there is infectious H5N1 virus in the wastewater.”
Swift said the county health department is working with the local utility, the state Division of Public Health and other agencies to continue testing and monitoring for the gene associated with the virus.
The scientists’ findings have prompted nine North Carolina environmental and animal welfare groups to advocate for more transparency from state officials, as well as “bold action” by the CDC “to determine the true extent of this outbreak before its threat to people, wildlife and farmed animals becomes impossible to contain,” according to a letter recently sent to U.S. centers for Disease Control and Prevention (CDC) Director Mandy Cohen.
Cohen was previously the North Carolina Secretary of Health and Human Services.
The CDC could not be immediately reached for comment.
H5N1 influenza emerged in wild birds in the late 1990s; and spread to backyard and commercial chicken and turkey flocks, including in North Carolina.
A new H5N1 strain has caused widespread outbreaks, and last year tens of millions of chickens were killed in the U.S. to control the transmission of the disease. This year the outbreak spread to dairy cattle and other animals.
Since 2022, there have been three cases of H5N1 in humans, none in North Carolina, federal data show. Two cases have been documented in farmworkers, one in Texas, and another in Michigan, earlier this spring.
There have been no reports of farmworkers in North Carolina contracting H5N1, state health officials told Newsline. But testing is not required. The CDC recommends testing only for people showing signs or symptoms of acute respiratory illness and who have been exposed to the virus.
In their letter, the environmental and animal welfare advocates asked Cohen to “significantly increase” the number of dairy workers tested for H5N1, “proactively test people in non-dairy animal agriculture operations to improve early detection and response for further potential outbreaks of this virus.”
The scientists’ recent discovery underscores the importance of wastewater monitoring for pathogens. This includes viruses thought to be primarily found in animals, but with potential to jump to humans, known as “zoonotic transmission.”
“There is increasing evidence” of zoonotic transmission of H5N1 to humans, “representing a potentially significant threat to public health,” the scientists wrote, adding the study’s findings also “highlight the need to consider industrial and agricultural discharges into wastewater.”
The wastewater detections provide key information, especially in North Carolina, where there is a lack of transparency about agricultural operations. The locations of any type of farm with a disease outbreak is confidential and known only to state agricultural and health officials.
But in general, while cattle operations must have a state permit – and their addresses are public – state law exempts most poultry farms from permitting. Their addresses are not known, even to the N.C. Department of Environmental Quality.
The N.C. Department of Agriculture houses the confidential poultry farm records, a practice that environmental advocates have long opposed.
The environmental and animal welfare advocates are asking for more detailed geographic data to become public, “while protecting privacy rights of workers.”
Milk, animal by-products, likely source of H5N1 gene in Forsyth County wastewater
The Stanford and Emory scientists monitored wastewater for a different Influenza A gene – which does not cause avian flu – from July 2023 until late April 2024. They collected samples from 190 treatment plants in 41 states and noted that at a third of those facilities, Influenza A concentrations were still high, even though the season had passed.
The scientists then turned their attention to retroactively testing those saved samples for the H5N1 gene. They chose the Forsyth County/Winston-Salem wastewater treatment plant, along with the four in Texas, because they had “remarkable increases” in concentrations of Influenza A and the respective public health departments approved the testing for H5N1.
A plant in Honolulu, Hawai’i, served as a control group because it didn’t have spikes of Influenza A or documented cases of H5N1 in animals.
Dairy cattle shed the virus in milk. While pasteurization kills the virus, it can persist in milk in a non-infectious form. And since milk containing the virus has to be diverted from the food supply, it would likely be discharged into wastewater treatment plants. The NC Department of Health and Human Services advises people not to consume or prepare food with raw or unpasteurized milk.
The Texas and Forsyth County/Winston-Salem wastewater treatment plants receive industrial discharges containing animal byproducts, including dairies and beef processing plants, the scientists wrote.
In Forsyth County, the uptick in H5N1 genetic material in wastewater occurred from April 5 through April 17; that coincided with the first report of the virus in a North Carolina cattle herd on April 9.
The herd was directly linked to the Texas outbreak, which occurred on March 24.
Dr. Mike Martin, the North Carolina state veterinarian, issued a “stop-movement” order to keep dairy cattle from affected herds from coming into the state, Heather Overton, spokesperson for the state Department of Agriculture, told Newsline. The department also required that the herd be isolated.
Despite the positive test, the North Carolina herd didn’t show symptoms of being ill, Overton said, but since then, the department has “worked with industry and our state and federal partners to inform consumers and protect the industry. We also currently follow all USDA guidelines and recommendations when it comes to movement of dairy cattle.”
The state agriculture department then lifted the isolation order on May 6, after several tests showed the virus was no longer present.
There are no current H5N1 cases in North Carolina poultry or dairy, Overton said.
While scientists have linked the recent findings to dairy cattle, “this doesn’t eliminate the possibility of contributions from other animals, including humans,” the scientists wrote. “Future work should further explore the possible contributions of animal shedding to municipal wastewater systems.”
The virus is still circulating in the wild bird population, with 29 cases in North Carolina since January, federal data show. Of those, 24 were reported in the eastern part of the state. The remaining five were detected in Buncombe County, with four, and Mecklenburg County.
Wild birds can infect backyard and commercial flocks. Of the 19 cases reported since 2022, 11 have been in commercial flocks with the remaining in backyard chickens.
From January through March, two commercial flocks accounting for 53,000 birds in Duplin and Lenoir counties were infected with the virus, state data show.
H5N1 has also been detected in 20 mammal species, including barn cats who became ill on farms around the same time as the virus broke out in dairy herds.
“A slow response” to the H5N1 virus “is inexcusable due to the painful lessons learned from COVID-19,” the environmental and animal welfare advocates wrote. “The CDC must respond to this outbreak with strong, proactive measures.”
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