Australian researchers today described how use of multiple attenuated herpesvirus vaccines in poultry led to the rapid emergence of two recombinant viruses more virulent than the viruses the vaccines were designed to battle. The group described its findings in a brief report in the latest issue of Science. In 2008 soon after a new vaccine against herpesvirus infectious laryngotracheitis virus (ILTV) in chickens was introduced in Australia, scientists detected novel genotypically distinct viruses from birds in several parts of the country. ILTV, also known as gallid herpesvirus 1, is one of the most contagious viruses that affects the poultry industry.
The authors hypothesized that the emergence of the new viruses could be related to a European vaccine strain first used in Australia in 2006. When they compared genetic sequences of the novel strains with the European vaccine strain and with two closely related Australian-origin ILTV vaccines that are also used in the country's poultry, they found that the novel viruses were mostly related to the European vaccine strain, though they also contained genetic material from the two Australian vaccine strains. Pathogenicity tests on the novel viruses found that they were more virulent and more able to replicate than the parent viruses. The researchers concluded that the recombination between attenuated herpesviruses is rare but can have serious consequences. They added that the findings have implications for other attenuated viruses.
Jul 13 Science abstract
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