 While living indoors decreases the risk of contracting certain diseases , living in close quarters with other rats , being unable to always seek proper protection from environmental factors ( e.g. temperature , humidity ) , being fed an unhealthy diet , and the stresses inherently associated with living in an unnatural habitat can all adversely affect a rat 's health to make them more prone to specific conditions . Specifically , <unk> 's disease , <unk> infections ( e.g. Giardia <unk> ) , and <unk> are usually seen in stressed or young rats . Additionally , pet rats are exposed to Streptococcus pneumoniae , a zoonotic disease caught from humans , not the same bacteria associated with strep throat . A human @-@ associated fungus , Pneumocystis carinii ( also found in almost all domesticated animals ) is usually asymptomatic in the rat , unless the rat 's immune system is compromised by illness . If this occurs the infection can develop into pneumonia . 
