While chlamydia is a significant concern in koala populations, not every koala is infected. The disease is widespread in many regions of Australia and poses a substantial threat, contributing to declining numbers and impacting individual koala health and species viability.
Prevalence and Specific Pathogen
The prevalence of chlamydial infection in koala populations varies considerably, ranging from zero to as high as 89% in some areas. Clinical disease ranges from 4% to 44% of infected individuals. Northern koala populations often experience more severe chlamydial disease compared to their southern counterparts.
Two bacterial species, Chlamydia pecorum and, less frequently, Chlamydia pneumoniae, are responsible for chlamydiosis in koalas. C. pecorum is the main cause of disease, while C. pneumoniae appears less pathogenic. These koala-specific strains are distinct from Chlamydia trachomatis, which causes human STIs. Research suggests some koala strains of C. pecorum are genetically similar to those found in livestock, suggesting a possible cross-over from agricultural animals.
Impacts on Koala Health
Chlamydia causes severe health problems in koalas, impacting their health and reproductive success. Ocular disease, known as keratoconjunctivitis, is a visible symptom. This condition involves inflamed eyes, often with discharge, leading to severe swelling and, if left untreated, permanent blindness. Blindness impairs a koala’s ability to find food, navigate, and escape predators, often resulting in starvation or increased vulnerability.
Urogenital tract infections are also common. These can lead to infertility in both male and female koalas, with females developing ovarian cysts. Urinary tract infections can cause bladder wall thickening, pain, and incontinence, a condition colloquially known as “wet bottom,” characterized by constant urine leakage. Chlamydia can also lead to pneumonia, compromising respiratory health. These symptoms contribute to population declines by reducing birth rates and increasing mortality.
Transmission and Ecological Factors
Chlamydia spreads among koalas primarily through direct contact, including mating, making it a sexually transmitted infection. Young koalas can also acquire the infection vertically from their mothers, either during birth or by consuming “pap,” a specialized fecal material. Environmental exposure to contaminated surfaces or discharges (fomites) also contribute to transmission.
Beyond direct transmission, ecological factors exacerbate the spread and severity of chlamydia in koalas. Stress from habitat loss and fragmentation forces koalas into smaller, more crowded areas, increasing contact rates and disease transmission. Overcrowding can also lead to weakened immune systems, making koalas more susceptible to severe infection. Climate change, including heatwaves and droughts, further stresses koala populations, impairing their immune responses and heightening their vulnerability to chlamydial disease. Co-infections with other pathogens, such as koala retrovirus (KoRV), can also worsen chlamydial disease progression, leading to more severe outcomes.
Conservation, Management, and Human Interaction
Efforts to combat chlamydia in koalas involve a multi-faceted approach, including medical treatments and habitat management. Vaccination programs are underway, with trials showing promise in protecting koalas from developing severe disease and potentially reducing mortality. A vaccine developed by the University of the Sunshine Coast has been shown to push back the average age of disease onset and reduce deaths by at least 65% in wild populations.
Antibiotic treatments are available for infected koalas, though they present challenges because antibiotics can disrupt the koala’s gut microbiome, which is essential for digesting eucalyptus leaves. This disruption can lead to weight loss and, in some cases, death. Beyond direct medical interventions, conservation strategies focus on reducing environmental stressors by protecting and restoring koala habitats. Creating undisturbed forested areas and mitigating threats like vehicle strikes and dog attacks are important for koala health.
There is no evidence that the strains of Chlamydia pecorum or Chlamydia pneumoniae found in koalas are transmissible to humans. Therefore, direct transmission of chlamydia from koalas to humans under normal circumstances is highly unlikely.