July 16, 2012

Australia ILTV chicken vaccines reform into new virus

Viral strains, used in chicken vaccinations against ILTV, have recombined to create a new virus in Australia.

Researchers report genomic evidence in Science recently 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 eight and class nine. 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.

The research paper is titled, "Attenuated Vaccines Can Recombine to Form Virulent Field Viruses".