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, Tyzzer's disease, protozoic infections (e.g. "Giardia muris"), and pseudotuberculosis 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 pneumonia. 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.