Summary

Purified phase I rickettsial suspension was obtained from the spleen of mouse infected with Henzerling strain Q fever by differential centrifugation, trypsin digestion and ether treatment. ELISA coating antigen of Q fever was then prepared by further disruption with ultrasonic wave and high speed centrifugation. The antibody of the infected guinea pig was detected by indirect method of ELISA by antigen coated microtitreplates with protein concentration of 7.89 μg/ml. The positive rate accounted for 40% 4–5 days, 68.7% 6–7 days and 100% 8 days after infection. By agglutination test, however, the same sera were all negative within 7 days after infection, 20% 8–9 days and all positive 18 days after inoculation. ELISA reached the peak titre (1:64–1:1024) on the 24th day after infection whereas agglutination test in the same period only gave a titre of 1:8–1:32, and reached its peak titre (1:128–1:256) 1 month after infection. Since the Q fever antibody of the guinea pig could be detected 66.7% as positive 1–2 days after fever onset by the ELISA indirect method, the ELISA appears to be a more ideal method for early diagnosis of Q fever than other serological methods.