Outbreak of an Emerging Recombinant of Myxoma Virus ha-MYXV in European Brown Hares (Lepus europaeus) in Austria.

Myxomatosis, caused by the myxoma virus (MYXV), is a severe disease primarily affecting European rabbits (Oryctolagus cuniculus), with very high case fatality rates. Historically, MYXV was introduced to Europe and Australia in the 1950s to control rabbit populations, becoming endemic and undergoing genetic adaptations. In 2018, a novel recombinant variant, hare-adapted MYXV (ha-MYXV), emerged in Spain, causing significant declines in Iberian hare (Lepus granatensis) populations. This study reports the first outbreak of ha-MYXV in Austria, severely affecting European brown hares (Lepus europaeus) and wild rabbits during 2025. Between March and November 2025, 272 hare and 12 rabbit carcasses were submitted for investigation. Pathological examinations revealed characteristic swelling and inflammation around the eyes, nose, and genital tract, accompanied by histological epithelial changes consistent with a poxvirus infection in 235 European brown hares and 10 wild rabbits from 89 municipalities in Austria. PCR analysis and cytopathic effects (CPEs) observed in rabbit kidney 13 (RK13) cell culture confirmed the presence of MYXV. Sequencing further identified a typical 2.8 kb M009L gene insertion, definitively linking the outbreak to the highly pathogenic ha-MYXV variant. The outbreak spread across Vienna, Lower Austria, and Burgenland, with hunters reporting hundreds of additional unsubmitted cases. The emergence of ha-MYXV in Austria highlights the virus's geographic expansion, possibly facilitated by human-mediated transport of infected animals or vectors. The outbreak also underscores the potential indirect One Health risks posed by coinfections with zoonotic bacteria in affected hares and emphasizes the need for enhanced surveillance, genomic analysis, more targeted screening of potential vectors, and cross-border collaboration to monitor the evolution and spread of ha-MYXV, mitigate its impact on wildlife populations, and address associated public health concerns.