Virus strains used to vaccinate chickens against ILTV have recombined to form a virus in Australia. Researchers report genomic evidence in Science this week that attenuated vaccines can recombine to form new virulent viruses.
Farmers fight herpesvirus ILTV (infectious laryngotracheitis) in chickens by vaccination using attenuated herpseviruses. Three vaccines in use in Australia, two produced by Pfizer and one from European company Intervet have resulted in the appearance of two new strains of ILTV, named class 8 and class 9. These new strains are becoming more prevalent and are just as deadly as the previous ILTV strains.
Scientists at the Asia-Pacific Centre for Animal Health, at the University of Melbourne, Australia, tested the genomes of the new strains and the vaccines, and found that the new viruses’ genome is a patchwork made up of the three herpesvirus vaccines. The results were published in Science.
Given that farmers generally do not use both vaccines on the same animal, the recombination suggests that the vaccine strain first spread to a non-vaccinated population before moving into an animal population vaccinated with a different strain.