United States: An alarming uptick in influenza viruses identified at wastewater treatment facilities across California has incited apprehension that the H5N1 avian flu might be disseminating more swiftly than forecasted, potentially jeopardizing the state’s 1.7 million dairy cows.
Health authorities have documented multiple surges in influenza A viruses, including the H5N1 strain, which has decimated avian populations globally and afflicted numerous dairy herds in nine US states, according to the reports by the San Francisco Chronicle.
The Bay Area has emerged as a significant epicenter of flu activity, as evidenced by data from approximately 700 sites published by the Centers for Disease Control and Prevention. Nearly all monitored locales in the vicinity indicate moderate to substantial elevations in influenza A virus levels.
While the confirmation of avian flu remains elusive, its potential presence cannot be discounted.
A representative from the California Department of Public Health (CDPH) informed the Chronicle that they are scrutinizing this surge, which deviates from conventional human influenza patterns, as it is not mirrored in general populace illness reports.
Typically, the circulation of influenza A, the type more commonly causing flu in adults, wanes significantly after the winter flu season’s zenith. The current escalation suggests an anomaly.
Although avian flu poses minimal threat to humans, its propagation among livestock could disrupt food supplies and potentially precipitate a pandemic if it mutates to facilitate human-to-human transmission, as per the San Francisco Chronicle.
Presently, no instances of infected herds have been reported in California, the foremost milk-producing state in the US, hosting around 1,300 dairy farms.
The CDPH is actively collaborating with the CDC, local health departments, and wastewater utilities to probe these increases, “including testing specifically for evidence of H5N1 in multiple sewer sheds throughout the state,” the agency stated.
To date, no human cases of H5N1 infection have been identified in California.
Existing wastewater monitoring techniques can detect the presence of influenza A viruses but cannot discern their specific subtype. This limitation implies that while they can detect avian influenza H5N1 viruses, they cannot differentiate them from other influenza A virus subtypes.
Despite avian flu viruses typically not infecting humans, there have been documented instances of human infection. According to the World Health Organization, between 2003 and 2024, there were 889 reported cases of avian flu globally, with a fatality rate of approximately 50%. The possibility of additional asymptomatic infections during this period remains uncertain.
Individuals working on dairy and poultry farms are at elevated risk of infection due to direct contact with chickens and dairy cattle. Although avian flu has been identified in various mammalian species, including sea lions, cows are particularly concerned due to their frequent interaction with humans and their critical role in the food supply chain.
The precise mechanism of avian flu transmission to or among cattle is not fully elucidated. It could transpire through infected feces, including aerosolized fecal particles in dust. Additionally, there have been cases of cats contracting the virus after consuming raw milk from infected cows.
The current avian flu strain emerged among birds in 2022 and was first detected in US dairy cows in late March, marking the inaugural known instance of bird flu viruses in cows.
Since then, it has disseminated to 49 dairy herds across nine states: Texas, Michigan, Kansas, Colorado, Idaho, New Mexico, North Carolina, South Dakota, and Ohio, as per the Department of Agriculture.
There have been only three reported avian flu infections in individuals in the United States. One case occurred in Colorado in 2022 involving a person working closely with infected poultry. The other two cases were more recent — one in Texas in March and one last week in Michigan — involving individuals employed at dairy farms.
In the most recent case, a “notable change” in the virus’s genetic composition was observed, enhancing its adaptability to mammalian hosts, according to a CDC update published Friday.
In the earlier cases, the individuals experienced mild symptoms such as fatigue and conjunctivitis and eventually recovered. The outcome of the third case remains to be determined.
“We continue to investigate, and when we have something to report, we will let you know,” the CDPH stated.