The genome of the cuddly-looking koala (Phascolarctos cinereus) is being invaded by a retrovirus, and researchers are using the polymerase chain reaction (PCR) and other genetic techniques to learn more, according to research published in PLoS One.

Australian koala with her baby

Credit: ©hotshotsworldwide/Fotolia

The koala retrovirus (KoRV) causes koala immunodeficiency syndrome (KIDS), and has been linked with the high incidence of chlamydiosis, leukaemia, and lymphoma seen in these marsupials, threatening an already damaged population. KoRV is widespread in northern Australian koalas, but less common in southern Australian mainland and island populations.

To reproduce, retroviruses need to copy their genetic material into the genes of cells in the host animal. If these are reproductive cells, the changes can be copied to the next generation. According to the researchers, this is the only retrovirus currently known to be currently invading the germline (the cells that become eggs and sperm) of its host. An international team of researchers from Germany, Austria and the USA used polymerase chain reaction (PCR) based methods to look at viral genomes in museum samples, and then built on this research to find out more about the evolution of the KoRV genome.

Koala #2

Analysing samples of DNA taken from modern-day animals, and comparing these with samples from museum exhibits up to 130 years old allowed the researchers to see how the virus genome has changed over more than a century. Adding in complex mathematical protein modelling revealed that overall, the virus was very stable and had changed little over 130 years, with new variants appearing only relatively recently.

“The results suggest that the endogenisation of a retrovirus may happen frequently and rather rapidly, initially without much change inside the virus and that becoming a part of the genome of all members of a host species takes a very long time,” said principal investigator Alex Greenwood.