Rimondi, A. | Search bioRxiv

bioRxiv2024

Massive outbreak of Influenza A H5N1 in elephant seals at Peninsula Valdes, Argentina: increased evidence for mammal-to-mammal transmission

H5N1 high pathogenicity avian influenza (HPAI) viruses of the clade 2.3.4.4b have killed thousands of marine mammals in South America since 2022. In October 2023, following outbreaks in sea lions in Argentina, we recorded unprecedented mass mortality ([~]17,000 individuals) in southern elephant seals (Mirounga leonina) at Peninsula Valdes. Seal pups were disproportionately affected. Adult seals departed early, disrupting social and breeding structure. Frequent interactions with sea lions and scavenging by seagulls were observed. Deaths of terns concurred with seals but peaked weeks later. HPAI H5N1 was confirmed in seals and terns. Moreover, genomic characterization showed viruses from pinnipeds and terns in Argentina form a distinct clade with marine mammal viruses from Peru, Chile and Brazil. These mammal-clade viruses share an identical set of mammalian adaptation mutations which are notably also found in the terns. Our combined ecological and phylogenetic data support mammal-to-mammal transmission and occasional mammal-to-bird spillover. To our knowledge, this is the first multinational transmission of H5N1 viruses in mammals ever observed globally. The implication that H5N1 viruses are becoming more evolutionary flexible and adapting to mammals in new ways could have global consequences for wildlife, humans, and/or livestock.

microbiology↗

bioRxiv2022

Few amino acid mutations in H6 influenza A virus from South American lineage increase pathogenicity in poultry

In chickens, infections with influenza A virus (IAV) can range from mild to severe and lethal. The study of IAV infections in poultry has been mostly limited to strains from the North American and Eurasian lineages, whereas limited information exists on similar studies with strains from the South American lineage (SAm). To better evaluate the risk of introduction of a prototypical SAm IAV strain into poultry, chickens were infected with a wild-type SAm origin strain (WT557/H6N2). The resulting virus progeny was serially passage in chickens 20 times and the immunopathological effects in chickens of the last passage virus, 20Ch557/H6N2, was compared to those of the parental strain. Comparison of complete viral genome sequences indicated that the 20Ch557/H6N2 strain contained 13 amino acid differences compared to the wild type strain. Five of these mutations are in functionally relevant regions of the viral surface glycoproteins hemagglutinin (HA) and neuraminidase (NA). However, despite higher and more prolonged virus shedding in chickens inoculated with the 20Ch557/H6N2 strain compared to those that received the WT557/H6N2 strain, transmission to naive chickens was not observed for either group. Analyses by flow cytometry of mononuclear cells and lymphocyte subpopulations from the lamina propria and intraepithelial lymphocytic cells (IELs) from ileum revealed significant increase in the percentages of CD3+TCR{gamma}{delta}+ IELs in chickens inoculated with the 20Ch557/H6N2 strain compared to those inoculated with the WT557/H6N2 strain.

microbiology↗