Summary
We detected the highly pathogenic avian influenza A (H5N1) virus of Eurasian origin belonging to the Gs/GD lineage, clade 2.3.4.4b, in wild waterfowl in 2 Atlantic coastal states in the United States. Bird banding data showed widespread movement of waterfowl within the Atlantic Flyway and between neighboring flyways and northern breeding areas.
Two studies
Since the first description in 1996 of the H5N1 avian influenza A virus (AIV) and its ability to lethally infect humans, there has been concern about new strains arising from gene rearrangement. Zhu and colleagues now describe the increase in infections in poultry and humans in China caused by a novel reassortant influenza A (H5N6), which has replaced H5N1 as the dominant AIV subtype in Asian poultry and will likely be more easily transmitted to humans.
As with other AIV infections, exposure to live poultry was the most common factor in the acquisition of H5N6, and the most common presenting symptoms were fever and cough (which made initial distinction from other respiratory illnesses difficult). .
Among 66 cases in 2021, the risk of severe disease was 94% and mortality was 55%.
Two contemporaneous CDC reports on influenza A (H5N1) complete considerations of the current and future impact of AIV.
The first report involves a case of human H5N1 in an American poultry worker whose job was to cull sick birds from the flock. He was slightly ill and recovered. Although H5N1 has been found in poultry in 29 states and in wild birds in 34 states, given the patient’s close exposure to diseased poultry, this case is not believed to raise fears of increased risk in the general population.
In a second report, Bevins and colleagues used tracking data to show that migratory wild waterfowl have recently transported the highly pathogenic H5N1 AIV to the eastern US via the Atlantic Flyway. Previous findings had considered the Pacific Flyway as the only source of import to the US.
The segmented genome of influenza A viruses allows for genetic reassortment along with co-infection of wild birds, which may confer increased transmissibility or pathogenicity, or both.
The fact that wild migratory birds carry these viruses, often asymptomatically, means that it will not be possible to eradicate AIV. Although transmission from birds to humans (usually after considerable exposure) causing high mortality rates is not uncommon, documented human-to-human transmission has been relatively rare. Our biggest concern is that reassortment and mutation in AIV will eventually affect this latter form of transmission, with potentially disastrous results.
