Second H5N1 Strain Detected in Cattle in the U.S.

A new strain of the highly contagious H5N1 avian influenza virus has been identified in dairy cows in the United States, marking a concerning development in animal health. The U.S. Department of Agriculture (USDA) announced that samples from dairy cattle in Nevada tested positive for the D1.1 genotype of the H5N1 virus, specifically from the clade 2.3.4.4b. This follows previous infections attributed to a different strain, genotype B3.13, that had been observed in cattle herds across the country since the spring of 2024.

The D1.1 genotype is currently the dominant strain found among North American migratory birds and has also been reported in various wild animals and domestic poultry. The identification of this second strain in cattle within a year raises alarm among researchers and health officials.

The Friedrich-Loeffler-Institut (FLI), a leading research institute for animal health in Germany, expressed serious concerns regarding the implications of this finding. The institute highlighted the critical nature of these occurrences, indicating that the ability of the virus to jump species is a significant risk. It remains unclear how the virus was introduced to the cattle herds in these cases.

Despite efforts, the initial outbreak of H5N1 in U.S. dairy cows linked to genotype B3.13 has not been fully contained. The FLI emphasized the urgent need to implement nationwide measures to prevent the spread of the newly identified D1.1 strain, learning from the previous year's events.

Prominent virologist Professor Martin Schwemmle from the University Medical Center Freiburg echoed these sentiments, noting that the detection of H5N1 in U.S. cattle serves as a stark warning. He indicated that the capacity of these viruses to breach species barriers poses a continuous threat. Although the exact source of infection in these animals is still unknown, there is a growing concern that similar incidents could arise in Europe, including Germany.

To mitigate the risks, authorities are urged to enhance biosecurity measures within cattle populations. It is recommended that any unexplained cases of mastitis in cows be subject to thorough diagnostic investigations to ensure swift identification and response to potential outbreaks.

This latest development occurs amidst ongoing worries about the H5N1 virus, which has already led to public health concerns. Reports of H5N1 infections in humans and the emergence of mutations have prompted vigilance among health authorities, as they assess the potential implications for both animal and human health.

As the situation evolves, stakeholders in agriculture and public health are closely monitoring the spread of avian influenza, ensuring that robust measures are in place to safeguard livestock and public safety.