Segregate, Test, Observe and Persevere (STOP): strengthening ex situ breeding programs for biodiversity in zoos amid highly pathogenic avian influenza threats - a case approach

Zoos with avian populations are vulnerable to incursions of the high pathogenicity avian influenza virus (HPAIV) H5Nx due to the free-range husbandry, bird population density and shared open water areas between zoo birds and wild waterfowl. An outbreak of HPAIV H5N1, clade 2.3.4.4b, genotype EA AB, at the Zoological Garden Karlsruhe, Germany, in 2022, was managed applying legal restriction measures but exceptionally exempting culling orders for RT-qPCR-positive but clinically healthy birds. A critical factor in the zoo's response was the implementation of a segregation concept approved in advance. The entire bird population could be rapidly separated into epidemiological housing units (epUs) cared for by separate staff. A total of 79 birds initially tested RT-qPCR-positive, but only 21 (26.6%) clinically diseased birds had to be euthanized or succumbed. Seroconversion amounted to 94.8% of the remaining 58 birds. Extensive RT-qPCR investigations of 3,634 samples confirmed infections remained confined to three initially infected epUs out of a total of 25. Spread of virus in the infected epUs was limited to 3 weeks after segregation. In the cohort of infected pelicans, surviving individuals remained seropositive with elevated levels of H5-specific antibody titers for the following 2 years suggesting ongoing protection. The described science-based control measures rested on a legally binding yet interpretive statement regarding the pertinent animal health legislation are exemplary for managing an outbreak of high pathogenicity avian influenza (HPAI) in zoos.