November 2024

Summary:

• • • Current situation on highly pathogenic avian influenza viruses (HPAIV) H5N1: Several human cases reported in the USA and Canada
    • High H5N1 activity in wild waterfowl and domestic poultry across Europe; numerous poultry farms affected in Austria
    • Currently no major risk of human-to-human transmission, but ECDC recommends close monitoring and targeted testing
    • Patients with acute respiratory symptoms should be questioned about avian influenza exposure and tested when appropriate
    • All routine influenza detection methods at the institute can detect H5N1; subtyping available upon request when suspected

HPAIV infections are zoonotic diseases caused by Influenza A, subtype H5 or H7. Wild waterfowl represent the natural host reservoir. Documented infections in humans are generally rare. Recently, however, several human H5N1 cases have been reported. According to reports from the US health authority CDC, several dozen human cases have already been reported in a few states, with apparent contact to agricultural operations (dairy farms).

According to reports from the Public Health Agency of Canada, one person in British Columbia is in critical condition following a confirmed H5N1 infection, without any travel history or traceable risk contacts. However, contact tracing and testing of additional contacts yielded no further cases. Therefore, there is currently no major risk to the general population from human-to-human transmission. In Europe as well, the risk of an H5N1 pandemic is currently assessed as low.

However, high H5N1 activity is currently being observed in wild waterfowl and in some cases also in domestic poultry in several European countries. Numerous poultry farms in Austria are also affected, where strict housing requirements and other preventive measures are currently in place. Due to the high, unpredictable potential for genetic adaptation that could result in easier transmission to humans as well as sustained human-to-human transmission, the European health authority (ECDC) recommends close monitoring and generous targeted testing in the coming winter season.

Due to the current epidemiological situation, patients admitted to hospital with acute respiratory symptoms should be questioned in their medical history about exposure to avian influenza and tested accordingly if appropriate. It is also recommended that all hospitalized patients with unclear viral encephalitis/meningoencephalitis in whom no other pathogen can be detected should be tested and subtyped for influenza viruses.

When severe respiratory infections requiring hospitalization occur in clusters, HPAIV should be considered as a possible differential diagnosis.

All our influenza detection methods that we use in routine practice also detect the Influenza A H5N1 virus. In case of suspected cases or upon request, subtyping for H5 genotypes can also be performed in our laboratory. If there is reasonable suspicion and this is entered into the electronic reporting system (EMS), the costs of the examination are expected to be covered by the provincial health directorate or the federal government.