Epidemiology and genetic characterization of myxoma virus from the first outbreak in Finland

Myxomatosis, caused by myxoma virus (MYXV), is a fatal disease of the European rabbit (Oryctolagus cuniculus). It has a worldwide distribution and has become an endemic disease throughout Europe since its introduction into the rabbit population in 1950. This study describes the first outbreak caused by MYXV in Finland in summer 2020. Eighteen feral rabbits collected during the outbreak and two during the following year were confirmed positive for MYXV using real-time PCR. Coinfection with rabbit hemorrhagic disease virus (RHDV) was observed in six cases. Whole genome sequencing of MYXV was performed for five rabbit samples collected during the outbreak in 2020 and two rabbit samples collected in 2021 to assess the origin of the virus and possible evolutionary mutations. Genetic characterization revealed that the genomes of the five samples collected during the outbreak in 2020 were identical. Phylogenetic analysis demonstrated the highest nucleotide identity to the German field strain FLI-H (99.97 %). The Finnish strains contain mutations that have not previously been described and may be responsible for changes in virus properties. On the other hand, the virus genome displayed only minor changes during the one-year follow-up in Finland. These findings add to knowledge of the spread of MYXV and its evolution.