Serological assessment of chlamydial infection in the koala by a slide EIA technique
H UENO,1 S MIZUNO,2 1 TAKASHIMAT, R OSAWA,1 W BLANSHARD,1 P TIMMS,4 N WHITE,3 N HASHIMOTO2
1 Department of Veterinary Public Health, School of Veterinary Medicine, Rakuno Gakuen University, Ebetu, Hokkai 069, Japan
2 Department of Veterinary Public Health, Faculty of Veterinary Medicine, Hokkaido University, Sapporo 060, Japan
3 Lone Pine Koala Sanctuary, Brisbane 4069
4 School of Life Science, Queensland University of Technology, Brisbane 4001
A rapid and simplified slide enzyme Immunosorbent assay (EIA) was developed for the diagnosis of chlamydial Infection In the koala. HeLa 229 cells Infected with koala strain Chlamydia psittaci were fled on the surface of multiwall slides and used as the antigen. The assay consisted of first reacting koala antiserum with the fled C psittaci antigen, followed by reaction with biotinylated rabbit anti-koala IgG, ABC reagent and substrate. The chlamydial EIA antibody titres obtained were compared with those of a complement fixation (CF) test using koala strain C psittaci as antigen. Of 35 koala sera tested, 16 CF positive sera (21:8) also had. A positive titre (21:200) In the slide EIA test (sensitivity 93.8%, 15/16). Nineteen CF negative sera were also negative in the slide EIA (specificity 100%, 19/19). Sixty-eight samples of koala blood were collected by ear-pluck using a sampling paper method and were assayed by both tests. Sensitivity of the slide EIA was 100% (15/15) and specificity of the test was 96.2% (51/53). To simplify the slide EIA for use as a practical screening test, a 3-polnt serum dilution series (1 1:200, 1 :400) was used. This 3-polnt slide EIA was compared with the CF test using sheep strain chlamydial antigen. Thirty-nine sera were assayed by both tests. The sensitivity of the 3-polnt method was 85.7% (6/7) and the specificity was 71.9% (23/32) as compared with the sheep antigen CF test. Of the 10 koalas with discrepant results, 8 (slide EIA positive but sheep antigen CF negative) were either chlamydia positive in cell culture or had evidence of clinical symptoms. This suggests a significant superiority of the slide EIA for detecting Infected animals as compared with the sheep antigen CF test. The 3-polnt slide EIA was also applied to cephalic vein blood collected on sampling paper and good agreement was obtained in 25 of 26 (96.1 samples when compared with those of serum samples. These results show that the slide EIA Is at least equal to the koala antigen CF test, and significantly more sensitive than the sheep antigen CF test for the serological assessment of chlamydial Infections In koalas.