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Chicken vaccines combine to form new ILTV viruses

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.

New strains
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.

Genome testing
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 Attenuated Vaccines Can Recombine to Form Virulent Field Viruses, can be found behind a pay-wall at Science magazine.

Editor WorldPoultry

One comment

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    George Arzey

    Contrary to Science July 13th 2012, recombination of herpes viruses including ILT viruses has been reported earlier ((Henderson LM et al., Am. J. Vet. Res.52, 820-825, 1991. Kan MG and Kim SJ, Vet Microbiology 83, 321-331, 2001)

    Most importantly, one of the cardinal rules governing the conduct of sound scientific experiments is to include an untreated group in the experiment in order to be able to demonstrate that whatever differences are observed between treatments, they are associated with the specific treatment. Indeed such a group was included; however, significant difference was not shown between it and the groups that received the treatments. The virulence of the recombined virus (as demonstrated by the impact on weight gain was therefore not demonstrated.

    Furthermore the claim that 17.6% mortality was reported in the field by Devline (Devlin et al., Vaccine 29, 5699,2011) is incorrect and carefully reading the Devlin paper published in Vaccine would reveal that the mortality was not attributed in this paper to class 8 or 9 viruses.

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