The Koala crisis: habitat destruction and diseases threaten their future

Photo: phototrip.cz

Koalas have a highly specialized diet composed mainly of eucalyptus leaves. Although eucalyptus is normally toxic to most animals, koalas have a specialized organ called the caecum that allows them to break down the fibrous leaves. Although koalas don’t have much competition for their food source, many factors put this population at risk of extinction.¹

The eastern and southern forests of Australia are home to koalas. This habitat is being destroyed by human deforestation as well as an increase in wildfires. Koalas are being forced from their habitats, seeking smaller patches of trees farther away from humans and as dogs, another major threat to their survival.

Being confined to smaller, more isolated forest areas has increased inbreeding within the species. This has resulted in an erosion of genetic diversity, reducing their ability to adapt to environmental threats. All of these factors are decreasing the koala’s ability to survive and thrive.

Through the efforts by the Austrian Federal and New South Wales Governments, researchers have gained more insight into the koala population’s genetics. Studies have shown that Victoria, Australia (Southern Australia) had the highest level of inbreeding. Additionally, many koalas in these regions are suffering from various diseases.²

A leading infectious disease in koalas is Chlamydia pecorum. It has become one of the key factors in the population decline, particularly in South-East Queensland and New South Wales.³ Chlamydial disease can cause inflammation, tissue fibrosis, urinary tract disease, and reproductive complications. In a population that is already dwindling, a disease that can lead to reduced fertility or infertility can become devastating.⁴

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Currently, investigators are studying the use of doxycycline 5 mg/kg every 7 days subcutaneously and chloramphenicol 60 mg/kg once daily subcutaneously for a duration of 28 days as treatment for chlamydial disease in koalas.Currently, investigators are studying the use of doxycycline 5 mg/kg every 7 days subcutaneously and chloramphenicol 60 mg/kg once daily subcutaneously for a duration of 28 days as treatment for chlamydial disease in koalas.⁴ However, studies conducted in 2023 following the 2019-2020 wildfires have shown that koalas are developing genetic resistance to both antibiotics. This study showed that fire-effect koalas had the highest frequency of antibiotic resident genes at 16.8%.⁵

Considerable efforts by the University of Sunshine Coast Animal Ethic Committee are focused on developing new vaccines for koalas. Researchers are not only a vaccine for chlamydia prevention, but also a exploring a combination vaccine for chlamydia and Koala Retrovirus (KoRV)-an infection linked to increasing rates of chlamydiosis and cancer.⁶ Although these studies show promising results, progression of studies may lead towards a more effective vaccine.

Koalas face a growing number of threats-from habitat loss and inbreeding to infectious diseases and antibiotic resistance.^1,2 With multiple organizations contributing ongoing research and conservational effort, there is hope for the survival of this species. Continued support and awareness are key to preserving the lineage of the koala for generations to come.

Samantha Gorski is a PharmD candidate studying veterinary pharmacy at the University of Connecticut in Storrs.

References

1. Interesting Facts About Koalas. Friends of the Koala. January 15, 2025. Accessed April 4, 2025. https://friendsofthekoala.org/about-koalas/?gad_source=1&gclid=Cj0KCQjwhr6_BhD4ARIsAH1YdjAxDODH1D5o3xzXyB8mTHtMRsFmLPm9zlhb8Xu3UJpNsTflxCPctIwaAtQREALw_wcB ‌
2. McLennan EA, Kovacs TGL, Silver LW, et al. Genomics identifies koala populations at risk across eastern Australia. Ecol Appl. 2025;35(1):e3062. doi:10.1002/eap.3062
3. Chen CJ, Casteriano A, Green AC, Govendir M. A retrospective study on antibacterial treatments for koalas infected with Chlamydia pecorum. Sci Rep. 2023;13(1):12670. doi:10.1038/s41598-023-39832-w
4. National Koala Disease Risk Analysis Report Version 1.2. May 2023. Accessed April 11, 2025. https://wildlifehealthaustralia.com.au/Portals/0/ResourceCentre/BiosecurityMgmt/KDRA%20Report%20v1.2_FINAL.pdf ‌
5. McDougall FK, Boardman WSJ, Speight N, et al. Carriage of antibiotic resistance genes to treatments for chlamydial disease in koalas (Phascolarctos cinereus): A comparison of occurrence before and during catastrophic wildfires. McDougall FK, Boardman WSJ, Speight N, et al. Carriage of antibiotic resistance genes to treatments for chlamydial disease in koalas (Phascolarctos cinereus): A comparison of occurrence before and during catastrophic wildfires. One Health. 2023;17:100652. doi:10.1016/j.onehlt.2023.100652
6. Quigley BL, Timms P, Nyari S, McKay P, Hanger J, Phillips S. Reduction of Chlamydia pecorum and Koala Retrovirus subtype B expression in wild koalas vaccinated with novel peptide and peptide/recombinant protein formulations. Vaccine X. 2023;14:100329. doi:10.1016/j.jvacx.2023.100329