Evaluation of latex agglutination for detecting chlamydial antibody activity in psittacine bird sera by comparison with direct complement fixation.

Abstract

Chlamydiosis in cage, domestic, and wild birds is caused by a gram-negative prokaryote, Chlamydia psittaci, which is an obligate intracellular parasite of a wide variety of host cells., Presentation of the disease can be subacute, acute, chronic, or the infection can be completely asymptomatic in mature avian hosts. Respiratory, digestive, urogenital tract, eye, and widespread systemic infections can occur. Because of the variability of clinical manifestations, it is difficult to diagnose the disease by simple clinical observation. Therefore, the use of laboratory tests to confirm or rule out chlamydiosis in live or dead birds is frequently necessary. 1,2,6,13,17,18,21 Different serologic tests have been used for detecting antibody activity induced by C. psittaci. One of the most commonly used tests has been the direct complement fixation (DCF). However, the serologic response of psittacine birds to C. psittaci is highly variable within and between species . 12,14 Nevertheless, a bird with a DCF titer ≥ 64 usually is considered to be currently infected. For rapid detection of Chlamydial antibody activity in psittacine birds’ serum, a latex agglutination (LA) has been described. Latex agglutination is a sensitive method that detected early Chlamydial antibody production in experimentally inoculated African grey parrots. The present study was undertaken to further evaluate the reliability of LA in the serodiagnosis of psittacine bird chlamydiosis. This was done by comparing LA and DCF test results. Two hundred fourteen sera were selected and divided into 3 groups for this study. Group I consisted of 82 sera from birds with various clinical signs such as lethargy, anorexia, sneezing, weight loss, conjunctivitis, diarrhea, yellow urate, hepatomegaly, splenomegaly, leucocytosis, and elevated SGOT enzyme. Group II consisted of 102 sera from birds with an unknown health status. Group III consisted of 30 sera from birds with a history of exposure to chlamydiainfected birds. Sera were from 5 different types of psittacine birds. In order to determine if there were any differences between titers in birds with early or chronic signs, Group I was further divided into 3 subgroups and results were tabulated accordingly: subgroup A birds were ill for 2-7 days; subgroup B birds were ill for 10-20 days; and subgroup C birds were ill for 21 days or longer. Antigen for DCF was made in cell culture and the test indicative of current infection with Chlamydia. Titers <32 were considered to be negative for a current Chlamydial infection. Antigen for LA was made in cell culture based upon the method described earlier. 13 LA was done by placing 10 μ1 of 1:20 serum dilution on a plate and 15 μ1 of a mixture of antigen and latex (volume ratio of 2:3) was added. The mixture was stirred and then rotated at 130 rpm for 2 minutes prior to reading results. Complete agglutination was considered as a positive reaction. Titers were determined by testing 2-fold serum dilutions. Results were analyzed by using the McNemar test for significance of changes? The data were summarized in a 2 x 2 contingency table. Results were termed significant by P < 0.05. Table 1 shows the number and percentage of positive LA and CF results. The highest percentage of positive results by LA (70.9) occurred with Amazon parrot sera, and macaw sera had the highest percentage (74.1) of positive results by DCF. The lowest percentage of positive LA results (46.6) was in conure sera and the lowest percentage positive by DCF (4 1.6) was in African grey parrot sera. These results in Table 1 correlate with those found when comparing the sensitivity and specificity of LA and DCF titer with Chlamydia isolation attempts. 13 Comparison of LA and DCF titers is shown in Table 2. The average percentage of LA titers, ≥ 16, and DCF titers, 264, on 214 birds tested was 67.7 and 65.4, respectively. Birds that were negative by LA and had low to moderate DCF titer (8-32) were considered to be birds with residual antibody from a past Chlamydial infection. Negative LA titers in birds that had DCF titers of 264 may have been the result