Prevalence of Pneumocystis carinii in wild rodents in Japan.

During the period from November 1980 to April 1984, 292 small wild rodents were captured in 6 localities in Japan. Eleven out of 142 Apodemus speciosus, 1 out of 11 A. argenteus, 4 out of 40 Microtus montebelli and 2 out of 3 Mus musculus were positive for Pneumocystis carinii. The intensity of infection was generally low and the infection rate did not show any significant difference between sexes of the host animals. The seasonal prevalence of infection in A. speciosus was not remarkable, but was somewhat higher in winter to spring than in summer to autumn. Also, the infection rate in A. speciosus was higher in relatively heavy body weights than in the lighter or the heaviest weight groups. This is the first report of P. carinii infection in wild rodents in Japan. We propose A. speciosus, A. argenteus and M. montebelli as the new natural hosts for P. carinii. No morphological difference was found between P. carinii in wild rodents, in rats and in man as far as the present light microscopic examination is concerned.