Allendorf, V. | bioRxiv Science

bioRxiv2025

Outbreak dynamics of high pathogenicity avian influenza virus H5N1, clade 2.3.4.4b euBB, in black-headed gulls and common terns in Germany in 2023

Since winter 2022/23, high pathogenicity avian influenza virus (HPAIV) H5N1 clade 2.3.4.4b, genotype euBB, has caused extensive mortality among wild birds. This genotype emerged in France in spring 2022 through reassortment between a gull-adapted low-pathogenicity virus and HPAIV H5N1. Phylogeographic and spatiotemporal analyses show that transmission into German breeding colonies of black-headed gulls (Chroicocephalus ridibundus) and common terns (Sterna hirundo) involved multiple independent incursions, likely via black-headed gulls returning from wintering grounds in the Netherlands, Belgium, and France. It spilled over into common terns, which breed in shared colonies with black-headed gulls, and led to high adult mortality in both species in 2023 (at least 8,137 black-headed gulls and 614 common terns; >3% of the breeding population), followed by significant breeding pair declines in 2024 (-15.9% in black-headed gulls, -5.8% in common terns). Increased immunity, at least in common terns, may have contributed to the apparent fade-out of genotype euBB. These findings highlight how integrating ornithological, epidemiological, and virological data can aid our understanding of viral transmission routes and population-level impacts, while also stressing that HPAIV should be added to the growing list of pressures on seabirds, a group that was already the most threatened among all bird taxa globally. Research Highlights- HPAIV H5N1 euBB caused mass mortality in gulls and terns in Germany in 2023 - Multiple independent viral incursions occurred into different parts of Germany - Serology showed survival and rising H5-seroprevalence in common terns - Outbreaks reduced the black-headed gull breeding populations by up to 24%

ecology↗

bioRxiv2023

Dogs and cats are less susceptible to the omicron variant of concern of SARS-CoV-2 - a field study

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused a pandemic of unprecedented extent. Beside humans, a number of animal species can be infected, however, in some species differing susceptibilities were observed depending on the virus variant. Here, we serologically investigated cats and dogs living in households with human COVID-19 patients. The study was conducted during the transition period from delta as the dominating variant of concern (VOC) to omicron (BA.1/BA.2) to investigate the frequency of virus transmission of both VOCs from infected owners to their pets. The animal sera were tested by surrogate virus neutralization tests (sVNT) using either the original receptor-binding domain (RBD), enabling the detection of antibodies against the delta variant, or an omicron-specific RBD. Of the 290 canine samples, 20 tested positive by sVNT, but there were marked differences between the sampling time, and, related thereto, the virus variants, the dogs had contact to. While in November 2021 infected owners led to 50% seropositive dogs (18/36), only 0.8% (2/254) of animals with household contacts to SARS-CoV-2 between December 2021 and April 2022 tested positive. In all cases, the positive reaction was recorded against the original RBD. For cats, a similar pattern was seen, as in November 2021 38.1% (16/42) tested positive and between December 2021 and March 2022 only 5.0% (10/199). The markedly reduced ratio of seropositive animals during the period of omicron circulation suggests a considerably lower susceptibility of dogs and cats to this VOC. To examine the effect of BA.2, BA.4 and BA.5 omicron subvariants, sera taken in the second and third quarter of 2022 from randomly selected cats were investigated. 2.3% (11/372) tested seropositive and all of them showed a stronger reaction against the original RBD, further supporting the assumption of a lower susceptibility of companion animals to the omicron VOC.

microbiology↗