#17,379
Today the USDA has updated their list of H5N1 detections in mammalian wildlife, adding 6 new cases (3 of which we've seen previously reported here and here), since their last update on March 17th. To date, 154 mammals have been identified in the United States, although this is almost certainly a significant undercount.
Peridomestic mammals, like red foxes and skunks, are the most commonly reported terrestrial mammals infected, although we are seeing an increasing number of big cats and bears being infected in recent months.
Earlier this month, in ECDC/EFSA Avian Influenza Overview December 2022 – March 2023, researchers described recent changes to the virus that may make it more of a threat to mammalian hosts.
Mutations identified in A(H5N1) viruses from mammals
About half of the characterized viruses contain at least one of the adaptive markers associated with an increased virulence and replication in mammals in the PB2 protein (E627K, D701N or T271A) (Suttie et al., 2019). These mutations have never (T271A) or rarely (E627K, D701N) been identified in the HPAI A(H5) viruses of clade 2.3.4.4b collected in birds in Europe since October 2020 (<0.5% of viral sequences from birds).
This observation suggests that these mutations with potential public health implications have likely emerged upon transmission to mammals. Moreover, the viruses collected in October 2022 from a HPAI A(H5N1) outbreak in intensively farmed minks in northwest Spain (Aguero et al., 2023) shows mutations in the NA protein which cause disruption of the second sialic acid binding site (2SBS). This feature is typical of human-adapted influenza A viruses, which may favour the emergence of mutations in the receptor binding site of the HA protein (de Vries and de Haan, 2023). These same mutations were detected also in seven A(H5N1) viruses from birds.
All of which means, that while often repetitive, reports of additional spillovers into mammals are of great importance.
The new additions to the list include:
Although surveillance and testing of wild birds is limited, H5N1 has now been reported in Alaska and all 48 of the lower states.
