Chlamydia psittaci latex agglutination antigen for rapid detection of antibody activity in avian sera: comparison with direct complement fixation and isolation results

Cell-culture-grown Chlamydia psittaci of turkey origin was treated with phenol and partially purified by differential centrifugation. The most stable antigen/latex mixture occurred with crude antigen precipitated by dimethyl sulfoxide and digested with trypsin. Agglutination reactions occurred within 2 minutes when antigen/latex and antibody-positive serum mixtures were rotated to facilitate contact of the reagents. Nonspecific agglutination of control latex occurred with 1.2% of clinical sera. When C. psittaci was isolated from feces from individual birds, latex agglutination (LA) and direct complement fixation (DCF) together detected antibody activity (titers greater than or equal to 8) in significantly more cases than did DCF alone. It follows, then, that an LA titer alone is highly indicative of a currently active infection or one that has occurred only recently. The isolation rate from birds that had no antibody activity detectable by LA or DCF was 3.8%. In tests on paired clinical sera, LA and DCF agreed in 72.5% of the cases regarding increased, decreased, or stable titers. For detection of antibody activity in single sera, LA had a sensitivity of 39.1% and a specificity of 98.8% relative to DCF detection of antibody activity. The high specificity corroborates the usefulness of LA as an indicator of current or very recent infection.