LCM infections are—or should be—particularly interesting to scientists for precisely the same reason that they're such a problem for pet suppliers. Like hepatitis B infections in newborn humans and rubella infections (German measles) in human fetuses, LCM in young mice and young hamsters is likely never to be fully erased by normal immune mechanisms. Instead, these young humans and animals develop a persistent tolerant infection, in which the infecting virus is treated by the body as a normal constituent rather than an invading pathogen. As the disease smolders, its victims leak infectious virus particles into the environment forever. Animals newly introduced into a pet supplier's colony will shortly become infected and pass on the epidemic. Persistent tolerant infections are often characterized by effects on the body that resemble other chronic diseases. Thus, LCM in mice may give us a good model for understanding some human conditions that seem related to long-standing, low-level illness.