The recent case reported in Nevada is significant as it marks the first instance of the D1.1 strain transferring from birds to cattle and then to a human. This particular genotype has demonstrated considerable danger; it is responsible for the only severe, deadly incident of H5N1 in the ongoing outbreak. In a case noted last month in Louisiana, the fatality was linked to interactions with both wild and domestic birds. According to the CDC, the individual had experienced “prolonged, unprotected” contact with these birds. Additionally, the D1.1 genotype was involved in a serious H5N1 infection that left a Canadian teenager requiring intensive care late last year.

A February 7 report from the USDA highlighted that the D1.1 strain detected in Nevada’s cattle carries a specific mutation, known as PB2 D701N, which enhances the bird-adaptive virus’s ability to replicate in mammals. This mutation has not been observed in the D1.1 strains affecting wild birds or in the B3.13 genotype found in dairy cows. However, it was noted in a 2023 case in Chile involving a human. The CDC confirmed that the D1.1 strain infecting the individual in Nevada also possesses the PB2 D701N mutation.

Both the USDA and CDC indicated that no additional concerning mutations were discovered, including one consistently seen in the B3.13 strain in cows. The CDC expects that the virus’s interaction with human immune responses or antiviral medications will remain unchanged.

Crucially, there has been no indication of human-to-human transmission, which would pose a significant risk of an outbreak. For these reasons, the CDC assesses the public’s risk as low; however, individuals who have been exposed to poultry, cattle, and birds should remain vigilant and take necessary precautions.

Overall, about 967 herds across 16 states have reported H5N1 bird flu infections, affecting nearly 158 million commercial birds since 2022.