Chlamydia pecorum infections in the koala are a significant contributing factor to their overall population decline (Fabijan et al., 2019; Nyari et al., 2017; Phillips et al., 2021). The development of an effective vaccine could play a crucial role in conservation efforts aimed at stabilising and restoring koala populations threatened by C. pecorum infections (Kollipara et al., 2012; Nyari et al., 2018; Phillips et al., 2019).
This study is an assessment of the efficacy of a koala anti-Chlamydia vaccine, in combating C. pecorum infections in a group of wild koalas in Southeast Queensland. The study involves 167 koalas (both male and female), with 55 receiving the vaccine (65% females), and 112 (56% females) remaining as unvaccinated controls. Over an 18-month period, samples were collected from ocular and urogenital sites at 6-month intervals for assessment of C. pecorum infections. All vaccinated animals were confirmed as C. pecorum negative by PCR assay at baseline. Analysis of urogenital tract infections at 6 months post-vaccination, revealed that vaccinated koalas consistently maintained a reduced C. pecorum prevalence (39%; 9 out of 23 koalas) compared to the unvaccinated Koalas (53%; 8 out of 15 koalas). At 12-months, the rates were 30% (11 out of 37 koalas) and 53% (8 out of 15 koalas), and at 18-months, were 13% (2 out of 16 koalas) and 35% (11 out of 31) for vaccinated and unvaccinated koalas respectively. Ocular infections showed similar trends however the number of infections were too low for analysis.
The overall results show that the vaccine exhibits a good level of protection against natural C. pecorum infection in the koala highlighting a 63% decrease urogenital tract infections after 18-months of vaccination.