Epizootiology of Chlamydia infections in two free-range koala populations

The prevalence of Chlamydia pecorum and Chlamydia pneumoniae infections in two free-range koala populations was assessed using genus-specific PCR comb ined with species-specific DNA probe hybridisation. Population A had a very high overall level of chlamydial infection (85%) with significantly more o f these infections being due to C. pecorum (73%) compared to C. pneumoniae (24%). The second population had a much lower prevalence of infection (10%) with equal levels of both species. An important finding of this study was that, while five of 24 C. pecorum-infected koalas had clinical signs of the disease (both ocular and urogenital sites), none out of seven C. pneumonia e-infected koalas had signs of clinical disease. This suggests that C. peco rum may be the more pathogenic of the two chlamydial species infecting this host. The level of infection (assessed by intensity of the specific hybrid isation signal) also differed between chlamydial species, with C. pecorum i nfections ranging from low to high grade whereas C. pneumoniae infections w ere always low grade. When the age of infected koalas was examined, 58% of young, sexually immature koalas were found to have C. pecorum infections, i ncreasing to 100% of koalas in the older age groups. This suggests that, in this population at least, young koalas are readily infected with C. pecoru m from their mothers. While the infection levels with C. pneumoniae were to o low to be statistically significant, again, sexually immature koalas were found to be infected. The recent separation of chlamydial infections in ko alas into two species is beginning to indicate different epizootiologies fo r koala C. pecorum compared to koala C. pneumoniae. (C) 1999 Elsevier Scien ce B.V. All rights reserved.