Transmission of Pneumocystis carinii   Disease from Immunocompetent Contacts of Infected Hosts to Susceptible Hosts

Abstract

Pneumocystis carinii organisms constitute a large group of heterogeneous atypical microscopic fungi that are able to infect immunocompromised mammals by an airborne route and to proliferate in their lungs, inducing Pneumocystis carinii pneumonia. This pneumonia remains a crucial epidemiological challenge, since neither the source of Pneumocystis carinii infection in humans nor the process by which humans become infected has been clearly established. Polymerase chain reaction (PCR) assays have shown that profoundly immunosuppressed patients without pneumocystosis can be subclinically infected with Pneumocystis. Other PCR-based studies have suggested that healthy immunocompetent hosts are not latent carriers of the parasite. However, recent reports have indicated that Pneumocystis carinii can persist for limited periods in the lungs of convalescent rats after recovery from corticosteroid-induced pneumocystosis, and also that immunocompetent mammals can be transiently parasitized by Pneumocystis carinii after close contact with hosts with Pneumocystis carinii pneumonia. Can transiently parasitized hosts be a source of infection for immunosuppressed hosts? In order to investigate this important clinical question, the ability of immunocompetent BALB/c mice, which were carrying subclinical levels of Pneumocystis carinii, to transmit the infection by the airborne route to highly susceptible, uninfected mice with severe combined immunodeficiency was studied. The results indicated that the immunocompetent mice, transiently parasitized by Pneumocystis carinii organisms after close contact with Pneumocystis carinii-infected mice, were able to transmit the infection to Pneumocystis carinii-free mice with severe combined immunodeficiency.

Genotypes at the Internal Transcribed Spacers of the Nuclear rRNA Operon of Pneumocystis jiroveci in Nonimmunosuppressed Infants without Severe Pneumonia

“…Airborne transmission of the fungus from host to host has been demonstrated in rodent models (5,12,34), and several observations suggest that interindividual transmission occurs in humans (for a review, see reference 10). Moreover, it is now widely accepted that the Pneumocystis organisms infecting each mammalian species are host specific and that the existence of an animal reservoir for P. jiroveci can be excluded, according to the available data (6).…”

“…Miller et al (23) have recently suggested that immunocompetent asymptomatic health care workers in close contact with PCP patients may have a potential role in the further circulation or transmission of the fungus. This hypothesis was prompted by the results of Dumoulin et al (5), who have shown that immunocompetent and apparently asymptomatic mice can be transiently parasitized by Pneumocystis after a brief contact with SCID mice with PCP and were able to transmit the fungus to other susceptible mice. Thus, experimental results have established that Pneumocystis organisms To the left of each line, the first number represents the NPA number and the second number represents the clone number.…”

Molecular typing of Pneumocystis jirovecii found in formalin-fixed paraffin-embedded lung tissue sections from sudden infant death victims

“…and that they can transmit the parasite to susceptible hosts by an airborne route (Chabé et al, 2004;Dumoulin et al, 2000).…”

Hypobaric hypoxia-related impairment of pulmonary surfactant proteins A and D did not favourPneumocystis cariniiFrenkel 1999 growth in non-immunocompromised rats

“…However, asymptomatic colonization or sub-clinical P. jirovecii infection has been reported in apparently immunocompetent subjects or in patients with slight immunodepression but with lung disorders such as chronic obstructive pulmonary disease (COPD) (Cano et al, 1993;Calderon et al, 1996;Miller et al, 2001). Consistently, recent experimental research has shown that Pneumocystis organisms are able to replicate in the lung of immunocompetent hosts (Chabé et al, 2004) keeping intact their pathogenic power, as attested by the fact that Pneumocystis cells were able to infect susceptible hosts by airborne route in which they induced Pneumocystis pneumonia (PcP) (Dumoulin et al, 2000;Gigliotti et al, 2003;Chabé et al, 2004). Thus, though immunocompetent hosts are usually able to radically eliminate the parasites from their lungs (Sepkowitz et al, 1993), as long as they remain infected they are able to transmit the infection either to naive healthy hosts, which will develop a primary infection, or to immunosuppressed hosts, which may then develop PcP.…”