How world's smallest DNA virus evolved in rare parakeets

The Mauritius parakeet was saved from the brink of extinction 30 years ago, thanks to the work of an international team of conservationists, including scientists from Kent. Now an outbreak of deadly Beak and Feather Disease is once again raising the spectre of extinction.

But a team led by Dr Jim Groombridge, of the University's Durrell Institute of Conservation and Ecology (DICE), has been able to make use of its archive of DNA samples from Mauritius parakeets, built up over many years, to identify how the world's smallest DNA circoviruses have evolved to cause the spread of the disease.

Dr Groombridge said: 'Circoviruses are amongst the smallest and simplest of all DNA viruses and detailed knowledge of how they evolve has largely remained a mystery, but the outbreak of Beak and Feather Disease ironically presented our team of scientists with the rare opportunity to gain an insight into the evolution of what is a poorly-characterised virus in a wild population.

'We were able to analyse viral DNA extracted from Mauritius parakeet blood samples which had been taken from the population annually as part of the routine field monitoring programme. Fortuitously, this 16 year archive of samples encompassed periods before, during and after the outbreak, allowing an analysis that would document the event as it happened.

'What our team found was remarkable: immediately prior to the outbreak, two mutations were pin-pointed to have occurred within a gene of the virus that is involved in viral replication. The exact functional nature of these changes and how they elicited the outbreak is presently unknown.'

The team's findings, published in the Journal of Virology, are exciting for scientists because the gene involved in viral replication, one of only two genes known for this virus, has always been considered to be relatively impervious to the influence of natural selection.

'Perhaps most remarkable of all was how the new mutant forms of the virus then quickly out-competed all other viral genotypes within the parakeet population. This phenomenon, known as a selective sweep, has never before been observed in such detail in a virus infecting a natural wildlife population,' said Dr Groombridge.

Now the team, made up of scientists from DICE, which is part of the University's School of Anthropology and Conservation, as well as Kent's School of Mathematics, Statistics and Actuarial Science, Wildlife Vets International, the Mauritius Wildlife Foundation, the Durrell Wildlife Conservation Trust and the Roslin Institute, have focused research on the immune system of the Mauritius parakeet. This will form part of continued international efforts to assist the Mauritius government to save this endangered species.