Quarantine any new ratties you bring home for a minimum of two weeks. one month is better. Quarantine means keeping the ratties in a different room. It means feeding the ratties you had longer before feeding the new ones. It means not holding the ones you had aready had after holding the new ones. Change your clothing between playing with the ratties you had had and the ones that are in quarantine. If you bring in more new ratties while you already have some ratties in quarantine... use a different room for them or start the two weeks all over if they share the same room. Quarantine is very important.
In the high plains of South Dakota, USA