During the spring 2024–25 outbreak of avian influenza A(H5N1) among dairy cattle, viral RNA was detected in a significant percentage of retail milk samples across the United States, according to a recent report. The findings suggest the virus was more widespread than initially understood, but that federal intervention improved detection and control efforts.
Early Spread and Detection Gaps
Researchers analyzed milk samples collected between April 13 and May 3, 2024, from 13 states. They found influenza A viral RNA in 36% of the samples. Notably, positive samples were identified in Arkansas, Indiana, Minnesota, Missouri, and Oklahoma – states that had not yet reported outbreaks at the time of collection.
As of April 12, 2024, only 29 infected herds had been officially reported. This number was inconsistent with the prevalence indicated by the milk sample analysis, leading researchers to conclude that many cases went undetected early in the outbreak. The Ohio State University College of Veterinary Medicine led the research team.
Improved Monitoring Through Regulation
The study compared the initial findings to samples collected from December 27, 2024, to January 29, 2025. During this later period, only 6.9% of retail milk samples tested positive for the virus. All positive samples from the later period were processed in California.
Following the implementation of federal directives in April and December 2024, which mandated increased testing, the number of reported infected herds rose to over 1,000. Researchers noted this increase was expected, as broader surveillance efforts naturally lead to the identification of more cases. The enhanced testing appeared to align infection patterns more closely with official detection numbers.
The researchers concluded that the early stages of the outbreak saw widespread, undetected cases in US dairy herds. However, they also found that federal regulations subsequently improved detection and contributed to controlling the spread of the H5N1 virus.
Frequently Asked Questions
What did the study find regarding the spread of H5N1 in milk?
The study found that influenza A(H5N1) viral RNA was present in 36% of retail milk samples collected between April 13 and May 3, 2024, from 13 states.
How did federal regulations impact outbreak monitoring?
Federal directives in April and December 2024 mandated increased testing, which led to a rise in reported cases to over 1,000 herds. This increased surveillance revealed infection patterns more closely aligned with official detection numbers.
Were all states equally affected by the virus?
The study found positive samples in five states – Arkansas, Indiana, Minnesota, Missouri, and Oklahoma – that had not yet reported outbreaks as of the time the samples were collected. Later, all positive samples were traced to milk processed in California.
Given the evolving nature of this outbreak and the impact of federal interventions, how might continued surveillance and research shape future strategies for managing avian influenza in livestock?
