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Koalas' Retroviral Response

Koalas are fighting off a viral invader on the genomic level, Agence France Presse reports.

It notes that a retrovirus, KoRV-A, has been infecting koalas for hundreds and possibly thousands of years. The virus causes Koala Immune Deficiency Syndrome, which AFP says is similar to human AIDS, but not as severe. Unlike human HIV, KoRV-A not only inserts itself into somatic cells' genomes, but it also burrows into the genomes of germline cells, enabling it to be passed on to infected koalas' offspring.

A new study appearing in Cell this week has found that koalas respond to this infection using piwi RNAs. "What we've uncovered, we believe, is an 'innate' genome immune system that can tell a virus from one of your genes," senior author William Theurkauf from the University of Massachusetts Medical School says in a statement. "We think this is getting at how your genome says, 'This is something we want; this is a gene.' And, 'That is something we don't want; that's a virus.'"