Cowpox

Cowpox virus, despite its name, circulates in (some species of) wild rodents in much of Europe and Asia, at least as far east as Kazakhstan.  Infection in cattle is rare; the disease is most commonly seen in domestic cats that, presumably, become infected through hunting.  Cats are also common liaison hosts - although cat-to-cat spread is rare, many human causes of cowpox can be traced back to an infected cat rather than to contact with a rodent.  Cowpox virus is closely related to, and antigenically very similar to, smallpox virus (now eradicated except for a few stocks kept for research), and was used by Edward Jenner to immunise people against smallpox.  This was the first 'vaccine' (from the Latin vacca meaning cow).