AN INHERITED virus may be the cause of chronic ill health in Australia鈥檚 koala populations. Although a viral cause has been suspected since 1988, a new study has found the first strong evidence to back this up.
Koalas are famously sickly. Up to 60 per cent of captive animals die from leukaemia or lymphoma. And they are plagued by chronic chlamydia infections, an indicator of a suppressed immune system.
In cats, these diseases are triggered by a retrovirus. Retrovirus-like particles were first identified in koalas with leukaemia in 1988, but it has proved difficult to pin these down as the cause. 鈥淚nherited retroviruses are very common and most are inactive,鈥� says Paul Young of the University of Queensland, who led the new study.
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Blood samples taken by his team from 120 wild and captive koalas from across Queensland all tested positive for a retrovirus called KoRV. But significantly, the team found that those koalas with leukaemia or lymphoma had a significantly higher level of KoRV. Wild koalas with chlamydia infections also had more of the virus in their blood, suggesting that KoRV really is associated with the diseases, Young says.
KoRV is closely related to a virus that causes leukaemia in gibbons. The most likely explanation for this is that a common host, perhaps a rodent, infected both koalas and gibbons within the last 200 years.
Retroviruses are capable of integrating into the DNA of their hosts and so can be inherited directly. But established ones tend to lodge at the same spot in the genome, and with the same number of copies. KoRV has wide variations between strains, inserts in various places and with different numbers of copies, suggesting that it is still infectious and is in the process of settling in the koala genome.
The researchers hope that in the future they can breed from disease-resistant animals to restock depleted populations.