 Several diseases , like Rat Coronavirus Infection ( RCI ) , Sendai virus , and Murine Respiratory Mycoplasmosis ( MRM , Mycoplasma pulmonis ) , are prevalent simply because their highly contagious natures work in tandem with the way rats are kept in laboratories , pet stores , and by breeders . It should be noted , however , that MRM is far less likely to occur in laboratory rats than in those kept as pets . 
