Where does Pneumocystis jirovecii reside and how is it transmitted?
The definitive answers to these questions remain unanswered but data are emerging. As stated previously, Pneumocystis is host species-specific and thus humans cannot develop disease after exposure to infected animals. In the laboratory, lab animals have been shown to be a reservoir for the specific Pneumocystis that infects them and animal-to-animal transmission has been demonstrated to occur via an airborne route. Furthermore, both animals with PCP and animals who are colonized with Pneumocystis (defined as the presence of Pneumocystis in the absence of pneumonia) have been shown to be capable of transmitting the infection to other animals. In clinical studies, emerging data suggests that humans are a reservoir for P. jirovecii. Early serologic studies demonstrated that exposure to Pneumocystis occurs early in life and that the majority of young children have developed antibodies against Pneumocystis by an early age. These studies support the traditional theory that PCP results from r
