Australia's koala population has been hit hard by two rapidly spreading diseases: chlamydia (a sexually transmitted infection) and a retrovirus similar to HIV. Scientists are working to develop vaccines, while lay citizens help care for sick koalas. Biologists say the epidemics, combined with other threats like habitat loss, pose a serious threat to the species.For more global science stories, visit: http://www.world-science.org/NOVA is produced by WGBH in Boston. National corporate funding for NOVA is provided by The Boeing Company. Major funding for NOVA is provided by David H. Koch, the Corporation for Public Broadcasting, and PBS viewers.