Australian Koalas are in danger of extinction because over half of them have chlamydia

Koalas live between 13 to 18 years in the wild. Males tend to not live near as long as the females due to their lives being more hazardous. They can all be subject to pathogens like chlamydia, too.

Among many issues it can cause reproductive tract infection. The infection easily spreads to mainland areas and the koala retrovirus can cause Koala Immune Deficiency Syndrome which is similar to AIDS. Koalas are close to extinction in Australia and a good portion of the reason is from diseases like chlamydia. Another portion is due to poaching the animals.

(Source)