Investigation into the Detection and Antibiotic Treatments for Chlamydiosis in Koalas

Abstract

The koala was listed as an endangered species due to a profound reduction of koalas in QLD and NSW, with chlamydial infections as the most observed bacterial disease across Australia. Clinical signs include conjunctivitis, urogenital/urinary tract inflammation causing infertility, and progresses to death if untreated. The thesis aimed to address the existing knowledge gaps and suggested future directions for managing chlamydial infections in this endangered marsupial.

The doxycycline dosage administered to diseased koalas at 5 mg/kg was evaluated with the PK/PD study using a two-compartmental analysis. PTA modelling and the AUC/MIC target of ≥24 were also investigated.

The retrospective study evaluated the treatment efficacy of antibiotics and the clinical outcome of hospitalised koalas. Female koalas exhibited lower odds of survival in comparison to males. Koalas given chloramphenicol treatment for ≥28d had increased odds of survival compared to those treated for <28d. Koalas administered doxycycline had higher odds of testing PCR negative compared to those treated with chloramphenicol. Female koalas had elevated odds of manifesting UGT signs and also increased odds of presenting both ocular and UGT signs compared to males. Notably, 28.5% of the koalas displayed no clinical signs but tested PCR positive.

The suitability of TRP, KYN, and KYN:TRP as potential biomarkers for chlamydial infections in the koala was studied. Plasma concentrations of TRP, KYN, and KYN:TRP were quantified in 35 clinically normal koalas, 35 with chlamydial infection and 10 with co-morbidities other than chlamydiosis. Reference ranges and optimal cut-off points were also proposed. Potential biomarkers, especially TRP, may not be specific for detecting C. pecorum, but KYN and KYN:TRP may have a role in identifying unhealthy koalas, irrespective of the underlying cause. This opened future research direction into the potential prognostic markers of detecting C. pecorum in the koala.