Transmission modes of Pneumocystis carinii among rats observed by karyotype analysis.

To observe the transmission patterns of karyotype of Pneumocystis carinii (Pc) by rat colonies, three strains of rats, Sprague-Dawley(SD), Wistar(W) and Fisher(F) from various animal vendors, were suppressed of their immunity by injection of methyl prednisolone. They were kept for 5 to 13 weeks in 3 different animal rooms, A, B, and C. The purified organisms were prepared in low melting point agarose gel by embedded lysis method for pulsed field gel electrophoresis. Field inversion gel electrophoresis showed 2 patterns of the karyotype of Pc. The rooms A and C contained SD rats from the source P, and also the room A was used for F and W rats. However, Pc from all of the SD and F rats in the room A showed same karyotypes, the pattern I. The SD rats from different vendors, M and S, were reared in the room B, and shared the same Pc karyotypes, the pattern II. The rats of W strain were from the vendor M, and immune-suppressed in the animal room A. Five weeks after the experiment, the Pc showed the karyotype pattern II but the pattern became mixed with the type I after 7 to 8 weeks. The findings revealed that the animals born and reared in the same animal quarter harbored Pc with same karyotypes. If the animals were kept under immune-suppression in the same room with heavily infected hosts, they could be infected by Pc from their neighbors. The present experimental findings suggest that Pc is transmitted among rats through the air.