What is known about the H5N1 virus identified in Nevada cattle?
A report published by the Animal and Plant Health Inspection Service (APHIS) of the U.S. Department of Agriculture (USDA) details the characterization of viral sequences obtained from the milk of Nevada cows infected with the D1.1 genotype (HA clade 2.3.4.4b).
The D1.1 viruses identified in dairy cattle in Nevada were found to be closely related to other D1.1 viruses recently detected in migratory wild birds across multiple North American flyways. Analysis of the hemagglutinin gene of the Nevada dairy cattle viruses did not reveal changes predicted to affect infectivity or adaptation to mammalian hosts. However, a mutation, PB2 D701N, commonly associated with the mammalian adaptation of highly pathogenic avian influenza (HPAI) viruses, was identified in viruses sequenced from four separate dairy cattle.
To date, this alteration has not been observed in D1.1 viruses found in wild birds or poultry and is absent in B3.13 genotype viruses detected in dairy cattle. The PB2 D701N mutation has previously been linked to mammalian adaptation due to its enhancement of RNA polymerase activity and replication efficiency in mammalian cells, potentially affecting pathogenesis in infected mammals. This change has been noted in human cases of HPAI H5. No additional mutations associated with mammalian adaptation were identified in the sequences. Notably, these D1.1 viruses sequenced from dairy cattle lack the PB2 - 631L marker, which appears to be fixed in dairy cattle B3.13 sequences. PB2-631L (encoded by bovine isolates) promoted influenza polymerase activity in human cells, suggesting a role in mammalian adaptation.
