The disease has reached the Chelyabinsk region of the Ural mountains which separate Asia from Europe.
The region is a major industrial center, whereas the other affected areas - Altai, Novosibirsk, Omsk, Tyumen and Kurgan - are mainly rural.
It is not yet clear whether the latest cases were caused by the strain which can be dangerous to humans.
A quarantine has been imposed in several villages in the Oktyabrsky district of Chelyabinsk - a rural district with hundreds of lakes.
