 Keeping rats as pets can come with the stigma that rats supposedly transmit dangerous diseases to their owners . One fear is that all rats carry plague , when in fact R. norvegicus is not among the list of species considered a threat . In 2004 , an outbreak of salmonella in the United States was connected to people who owned pet rats . However , it has been determined that a pet rat 's initial exposure to salmonella , along with many other zoonotic rat diseases , typically indicates exposure to wild rodent populations , either from an infestation in the owner 's home , or from the pet 's contaminated food , water , or bedding . 
