The viruses are mainly transmitted by Hyalomma ticks . Hyalomma ticks are originally native to warmer regions of south-east Europe and Asia, and adult specimens have also been found in Austria for several years.
The tick nymphs, the second developmental stage of a tick, arrive in Austria with migratory birds. As global warming progresses, it becomes more likely that the nymphs introduced in this way will develop into adults. This also increases the risk of the spread of new diseases such as Crimean-Congo fever.