Millions of chickens culled due to threat of bird flu
Emily Elkonin/Bloomberg via Getty Images
This year, the United States has seen its first reported death from bird flu, stirring apprehension regarding the possibility of a human pandemic. Although the virus’s spread has been contained sufficiently to conclude the emergency measures, health experts caution that vigilance remains crucial.
“The pandemic persists,” stated Megan Davis from Johns Hopkins University in Maryland. “The virus’s lethality hasn’t diminished.”
The predominant strain causing human infections is a subtype of avian influenza named H5N1, which was first detected in poultry in China back in 1996. After a resurgence in 2021, it wreaked havoc on bird populations worldwide and infected various mammals, including foxes, seals, and cats.
H5N1 is not well-equipped to infect humans and has not shown transmission capability between humans. However, it remains a grave concern; nearly half of the approximately 1,000 recorded global infections have ended in death since 2003. These fatalities are likely concentrated in severe cases, with many milder instances undocumented. Nonetheless, potential risks remain for the human population, especially if the virus adapts to enable human-to-human transmission, Davis emphasized.
Health experts expressed concern when H5N1 was identified among dairy cows in the U.S. in March 2024—the first confirmed case in this type of livestock. This not only placed the virus closer to human populations, particularly farm workers, but it also provided a prime opportunity for the virus to evolve and spread among humans. Each time it infects a new mammal, the pathogen stands to acquire mutations that could facilitate human transmission, according to Davis.
Since that time, H5N1 has been found in 1,080 herds across 19 states while monitoring a chicken farm. From February to mid-December 2022, around 1,950 birds were reported sick across the U.S., prompting the culling of nearly 200 million birds.
Subsequent outbreaks on farms triggered a significant uptick in human cases. As of December 2025, 71 individuals had tested positive for avian influenza in the United States; all knew of their infections through close contact with infected livestock or poultry. Out of these, three were infected by different animal sources, and although the cause for the remaining three cases remains unknown, there is no evidence suggesting they were transmitted from other humans.
Most affected individuals exhibited mild symptoms, such as conjunctivitis, and recovered fully. However, one person with pre-existing health conditions succumbed to the H5N1 virus in Louisiana, marking the first recorded bird flu-related death in the nation.
Since that incident, the United States has largely managed to curb the virus’s spread. The most recent positive testing for H5N1 occurred in February, according to Emily Hilliard, a representative for the U.S. Department of Health and Human Services. However, a man in Washington state later tested positive and died from a different strain of avian influenza, H5N5, after contact with infected birds in November .
“Somewhat reassuringly, retrospective analyses of fatal H5N5 instances have not indicated further human cases, although the potential for H5 viruses to incite a pandemic continues to loom, particularly given their capacity to affect mammals, including humans, and mammals’ potential for reciprocal transmission,” Davis pointed out. The CDC is actively monitoring the situation and asserts the threat to public health is currently low.
Cases of H5N1 in dairy cows have also significantly dwindled, with reports from the U.S. Department of Agriculture (USDA) citing only two flocks testing positive between November and mid-December.
These reductions ultimately led the CDC to conclude its emergency response to bird flu in early July, stated Hilliard. This response, which commenced in April 2024, enabled the agency to allocate additional resources and staff toward surveillance and containment efforts, she explained.
Several factors may have contributed to the decrease in cases. Notably, the Department of Agriculture implemented the National Milk Testing Strategy in December 2024, mandating dairy facilities to furnish raw milk samples for H5N1 testing. “Testing is central to any management program,” asserted Davis. “Without knowledge regarding its location, [H5N1] it would be impossible to enforce enhanced protective measures or request that farms enact quarantines.”
In February, USDA rolled out a $1 billion initiative aimed at reducing H5N1 occurrences within poultry farms, with increased funding earmarked for vaccine research and biosecurity protocols. One focus was to bolster defenses against wildlife. “The vast majority of [bird flu] outbreaks in poultry and livestock have been linked to contact with infected wild birds,” noted a USDA spokesperson. By curbing H5N1 spread on farms, according to Davis, the fact that most infections affect dairy workers likely contributed to lowering human transmission as well.
However, seasonal fluctuations could also play a role. “We experienced a drop during summer but subsequently witnessed a surge in cases during fall and winter,” remarked Davis. “Currently observing the migratory season, we are likely to see an increment in cases.”
This may account for the more than 200,000 increase in H5N1 detections among backyard and commercial poultry flocks, as migratory birds are known to spread the virus to farms during their seasonal flights, representing a rise of 130 percent between September and October. “What we haven’t seen is a considerable number of human cases,” Davis clarified. However, she added that it remains uncertain whether this is attributed to improved safety protocols or diminished monitoring of farm workers.
“It’s encouraging to observe the decline in cases,” stated Davis. “Nevertheless, we still have work to accomplish.”
Topics:
- bird flu/
- 2025 News Review
Source: www.newscientist.com
