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Researchers Find the Genetic Code for Creating Safer Vaccines for Infectious Laryngotracheitis

19 February 2013

Researchers based in Georgia, US, have identified several genetic changes as potential virulence factors of infectious laryngotracheitis virus (ILTV). They deleted one of the gene sequences from a virulent ILTV strain, which resulted in the attenuation of its virulence, showing this technique to have potential for the creation of future vaccines.

As part of this study, one of these gene sequences was deleted from a virulent ILTV strain and the virulence of the strain was attenuated as predicted.

There is an urgent need for an improved vaccine to protect chickens against infectious laryngotracheitis, a disease caused by a herpesvirus called infectious laryngotracheitis virus (ILTV), according to Dr Maricarmen Garcia of the University of Georgia and Dr Stephen Spatz of the USDA Southeast Poultry Research Laboratory in the US.

In a report of their work sponsored by the US Poultry & Egg Association, they explain that a vailable live vaccines are produced in either chicken embryos (CEO vaccine) or in tissue culture (TCO vaccine). Adaptation of the virus to grow in these systems attenuates the virus so that it can be used as a vaccine. Unfortunately, the vaccines have the potential to regain their original virulence if the vaccine virus spreads from chicken to chicken.

The genetic differences between the vaccine viruses and their parent strains, which provide the mild attenuated characteristics of the vaccine, have never been established. If these differences could be established, a strategy could be developed to design vaccines which are stably attenuated and that have significantly less likelihood of regaining their original virulence.

In their study, Drs Garcia and Spatz determined the full length genomes of the CEO vaccine and the TCO vaccine. These were compared to the full length genomes of the vaccine viruses after they were passed in chickens once and 20 times. The data were analysed to find the genetic changes that occurred as the vaccine viruses were passed in chickens and allowed to regain virulence.

The Georgia researchers identified several genetic changes as potential virulence factors of ILTV. These gene sequences may be used as potential targets for deletion in the creation of future vaccines.

As part of this study, one of these gene sequences was deleted from a virulent ILTV strain and the virulence of the strain was attenuated as predicted.

Garcia and Spatz concluded that understanding the genetic variation that exists between vaccine and virulent strains of ILTV facilitated the identification of genes encoding virulence factors and will allow for the genetic engineering of vaccines that are safe, stable and effective.

Find out more information on infectious laryngotracheitis (ILT) by clicking here.

February 2013



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