An outbreak of the chikungunya virus in the East African nation of Mauritius has prompted the CDC to place the country on its active travel health notice list. The move by the CDC extends the agency's current set of warnings against the chikungunya virus to a fourth country. What happened? As of May 14, the CDC had added Mauritius to its list of nations with active chikungunya outbreaks. Mauritius lies in the southwest Indian Ocean and is a maj…