A survey of birds in Denmark for the presence of Pneumocystis carinii.

One hundred eighty-three toluidine blue O-stained necropsy lung imprint smears from different avian species were examined microscopically for Pneumocystis carinii. No cyst forms of the organism could be identified. Seventy-eight serum samples from a total of 155 chickens were examined by a competition enzyme-linked immunosorbent assay (ELISA) for antibodies to P. carinii; 53 serum samples were from individual chickens, and 25 samples were pools of sera from two to five chickens. Diluted 1:50, the 78 serum samples showed a specific ELISA-inhibition of 4% to 56% (the 95% confidence limit being 25% to 30% inhibition). Diluted 1:50, nine serum pools representing 34 chickens and 17 of the 53 individual serum samples (32.1%) showed an inhibition greater than 30%. No specific pneumocyst DNA could be detected in serum from 13 of the 53 chickens using polymerase chain reaction and dihydrofolate reductase gene as a specific probe. Specific antibodies to a 116,000-molecular-weight antigen of rat pneumocysts were shown in two (13.3%) of 15 individual chicken serum samples. The results indicate that P. carinii organisms do not commonly reside in the lungs of birds, although some birds may be exposed to external sources of organisms.