Three vaccines used to prevent respiratory disease in chickens have swapped genes, producing two lethal new strains that have killed tens of thousands of fowl across two states in Australia, scientists reported on Friday.
The creation of the deadly new variant was only possible because the vaccines contained live viruses, even though they were weakened forms, said Joanne Devlin, lead author of the paper published in the journal Science.
Devlin and her team discovered how closely related the two new strains were with viruses in the vaccines after analysing their genes.
"What we found was the field viruses ... were actually a mixture of the genomes from different vaccine viruses," said Devlin, a lecturer at the University of Melbourne's School of Veterinary Science. "They actually combined, mixed together."
The viruses emerged in 2008, a year after Australia started using a European vaccine along with two very similar Australian vaccines to fight acute respiratory disease in poultry. The illness causes coughing, sneezing and breathing difficulties in birds, normally killing 5 percent of them.
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