Further Adventures Addendum

Since I posted, “Further Adventures of Avian Influenza” on 2/7/25 there has been some new information published by the APHIS lab (Animal and Plant Health Inspection Service) of the USDA. (Rather than post it only as a note, which many people say they have difficulty finding, I thought an addendum to Fridays post was worthwhile). The D1.1 genotype of H5N1 has very rapidly become the dominant avian influenza virus in North American birds, and it is a reassortment (exchange of large segments of genetic material) between two prior strains. Of some real concern is that the variant of D1.1 found now in cows in Nevada contains a mutation of the Pb2 gene (polymerase basic 2) predicted from experimental evidence to enhance the virus’ ability to replicate in mammalian cells, and also its pathogenicity for those cells. This is the first time this mutation has been detected, and it may be responsible for this genotype finally jumping into cows. The earlier appearing “Cow Clade” of H5N1 (B1.13), which has until now been the genotype infecting the dairy cows, contained a different mutation within the same gene, also predicted in advance to increase viral efficiency of replication in mammals. There is a distinct possibility that this version of the virus will spread widely in cows exposing human workers to a more virulent form of avian influenza. The further changes this virus would need to acquire to enable efficient transmission between people would likely be mutations in the N (neuraminidase ) gene, which controls the final stage of the viral life-cycle allowing massive release of new virions from the infected cell, and perhaps changes in the hemagglutinin (H) gene facilitating enhanced attachment to human airway receptors.