Koalas (Phascolarctos cinereus) may be one of the world's cuter critters, but that doesn't mean they have it easy. Not only have koala populations become heavily fragmented due to habitat loss, they face numerous threats that they never encountered before: household cats and dogs frequently kill koalas; hundreds die every year after being run over by cars and trucks; and now a deadly virus is spreading to koalas throughout Australia.
The koala retrovirus, which infects and alters the animal's DNA, has been linked to a variety of diseases and medical problems, including leukemia, bone marrow failure, cancer and AIDS-like immune deficiencies. First found in 2000, the retrovirus is already forcing some smaller koala populations into extinction, says Jon Hanger, director of research and ecological services at the Australian Wildlife Hospital. Hanger was the first person to genetically sequence the koala retrovirus after its discovery.