Natural transmission of Pneumocystis carinii in nonimmunosuppressed animals: early contagiousness of experimentally infected rabbits (Oryctolagus cuniculus).

Airborne transmission of Pneumocystis carinii has been established, but the infective form and the sources of infection remain unknown. Animal models for studies of P. carinii have previously been limited to immunosuppressed rodents; however, this study was performed with nonimmunodepressed P. carinii-free rabbits. This study was aimed at determining (i) the delay between inoculation of animals (day zero [D0]) and the onset of contagiousness and (ii) the end of contagiousness of these animals (donors). Five-week-old rabbits were used as contact animals and were housed with the donors. The cohabitation periods were for 4 or 5 days from D0 to D4, D4 to D8, D8 to D13, D13 to D18, and D18 to D22. The highest parasite burdens were observed in contact animals housed with donors from D8 to D13 or D13 to D18. This period (8th to 18th day following the day of inoculation of donors) might correspond to the highest phase of contagiousness of donors.