Prevalence of Pneumocystis carinii Delanoë & Delanoë, 1912 in rodents in Denmark.

Pneumocystis carinii has been found in 17 of 90 (19%) wild living trapped brown rats (Rattus norvegicus). The positive brown rats originated from about 25% of the trapping localities examined. Among brown rats of two breeding stocks, H and S, pneumocysts were found in 43.5% of the H rats, but in none of the S rats. By keeping brown H rats on a low protein diet for 8 weeks, it was possible to augment the prevalence to 53.8%. Pneumocystis carinii has furthermore been found in one of eight (12.5%) wild living long-tailed field mice (Apodemus sylvaticus), in one of 16 (6.3%) wild living house mice (Mus musculus), and in one of ten roof rats (Rattus rattus) of the Danish Pest Infestation Laboratory's breeding stock. Other rodent species, yellow-necked field mouse (Apodemus flavicollis), water vole (Arvicola terrestris), bank vole (Clethrionomys glareolus), field vole (Microtus agrestis), and an insectivor species, the common shrew (Sorex araneus) were all examined in small numbers, and were all negative for pneumocysts. Among rodents in Denmark. Rattus norvegicus seems to be the most important reservoir host for Pneumocystis carinii.