Avian influenza viruses (AIVs) pose continuous challenges to human and animal health worldwide. Wild birds are considered the natural reservoir for AIVs and play a major role in spreading influenza viruses over long distances. Highly pathogenic avian influenza (HPAI) H5N1 activity has increased globally causing mass mortality in wild birds and poultry and incidental infections in mammals. H5 clade 2.3.4.4 of the H5N1 subtype emerged in China in 2014 due to reassortment and then diversified into several clades. Clade 2.3.4.4b A(H5N1) viruses were detected in birds across the five continents. The spread of clade 2.3.4.4b of A(H5N1) viruses caused high mortality among domestic and wild birds. H5N1 clade 2.3.4.4b viruses have spilled over to several non-avian species, they were detected and isolated from domestic dogs and cats and from different species of marine mammals and minks. Epidemiological investigations based on serological testing showed that H5-specific antibodies were detected in foxes, polecats, and stone martens. These data showed that undetected and clinically mild HPAIV infections have occurred in wild carnivores in the Netherlands.

Some influenza viruses can propagate in rodents without adaptation. Previous studies showed the detection of (HPAI) H5N8 virus in a mouse that was found dead in a depopulated poultry house and antibodies against HPAI H5N1 virus were detected in rat sera during the initial outbreak of HPAI H5N1 virus in Hong Kong in 1997. Rodents can be abundant around poultry houses and share their habitat and may be contributing to the transmission of AIVs across poultry production sectors and across species. The recent outbreak of clade 2.3.4.4b of A(H5N1) viruses in dairy cattle across several states in the United States has raised significant concern nationally and globally. Human cases of H5N1 clade 2.3.4.4b virus infection from dairy farm workers were reported. Transmission of the virus from dairy cattle to other mammals including domestic cats was reported.

In 2021, the first HPAI H5N1 clade 2.3.4.4b viruses were detected in wild birds and domestic ducks from live bird markets in Egypt [16]. Based on the genetic analysis of HPAI viruses isolated in Egypt in winter 2021–2022, most H5N1 HPAI viruses were genetically close to H5 HPAI circulating in Europe, Africa, and the Middle East. Here, we report the first detection of HPAI H5N1 clade 2.3.4.4b viruses in wild rats in Egypt.