Australian scientists looking to vaccinate chicken populations against a respiratory disease may have accidentally unleashed a disease far more deadly than the one they hoped to prevent.According to a report published this week in Science, the genomes from two different strains of the herpesvirus infectious laryngotracheitis (ILT) virus that were used in vaccines have recombined to produce more virulent ILT viruses near Sydney and Melbourne.“These new strains were formed by recombination from the different vaccine strains and that they were actually more virulent than the vaccine strains that gave rise to them,” said lead author Joanne Devlin from The University of Melbourne, Parkville.Australian strains of ILT vaccine were first developed in the 1950s, but several problems were associated with their use, including the potential for the virus to lie dormant in a vaccinated bird until it can spread to unvaccinated populations.In 2006, Australian officials purchased a European strain of the ILT vaccine, which was then used to combat the virus. Two years later, deadlier strains of ILT began showing up in flocks. While the original strains typically killed 5% of the chicken population, the two new strains were killing up to 17% of chicken populations.At first, scientists theorized that the new vaccine’s weakened virus might have reverted back to a disease-causing form. However when the researchers sequenced the genomes of the viruses found in infected birds and the three vaccine strains; they realized that the new forms of the virus were composites of the European and Australian strains....MORE
HT: naked capitalism
