Received: November 15, 2019 Accepted: November 19, 2019 Published: November 19, 2019
Wild koala populations continue to experience serious declines as a result of several threatening factors including, (i) loss of habitat, (ii) motor vehicle trauma; (iii) dog attacks; (iv) infectious diseases, primarily Chlamydia but also the newly discovered koala retrovirus (KoRV). Chlamydial infections are associated with diseases ranging from ocular disease leading to blindness, as well as urinary and genital tract disease, leading to female infertility. Modeling shows that targeting chlamydial disease would have a major impact on stabilising population decline. Our preliminary studies have demonstrated that koalas can be safely immunized with a vaccine containing a mixture of chlamydial major outer membrane protein (MOMP) antigens combined with a single dose subcutaneous regime. We have recently completed several field trials with wild roaming koals are disesed animals coming into local wildlife hospitals. In the wild koala field trial we observed strong, specific and long-lasting immune responses in the vaccinated koalas; high titre antibody responses (as measured by ELISA and also in vitro neutralisation) as well as Chlamydia-specific cytokine responses (interferon-gamma and IL-17 in particular). For animals which were Chlamydia PCR positive at the time of vaccination, we observed a significant reduction in their infection PCR load (at both the ocular and urogenital tract sites). We also observed protection from progression to clinical disease in the vaccinated animals. We have also conducted a small trial to vaccinate animals which already have clinical signs of ocular disease. Instead of the normal practice of administering antibiotics (chloramphenicol, daily for 28 days, which severely disrupts the animal’s gut microbiome) we vaccinated four animals with a single dose, 3-MOMP vaccine. For all vaccinated animals, their Chlamydia PCR load decreased, and for 6 of the 7 animals, ocular disease regressed and the animals could be released back into the wild without further treatment. Our most recent vacine trial involves vaccinating against koala retrovirus. This has shown remarkable results with strong levels of neutralizing antibodies and a reduction in circulating viral load. These results are promising for the future development of a combined Chlamydia plus KoRV vaccine for use in captive as well as wild koalas.