Protection Induced in Broiler Chickens following Drinking-Water Delivery of Live Infectious Laryngotracheitis Vaccines against Subsequent Challenge with Recombinant Field Virus.

Mesula G Korsa,Alistair R Legione,Carol A Hartley,Glenn F Browning,Sang-Won Lee,Joanne M Devlin,Paola K Vaz,James R Gilkerson,Amir H Noormohammadi,Mauricio J C Coppo,Siba K Samal

doi:10.1371/journal.pone.0137719

Mesula G Korsa, Alistair R Legione + Show 9 more

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https://doi.org/10.1371/journal.pone.0137719

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Journal: PloS one	Publication Date: Sep 14, 2015
Citations: 7	License type: CC BY 4.0

Affiliation: University of Melbourne

Abstract

Infectious laryngotracheitis virus (ILTV) causes acute upper respiratory tract disease in chickens. Attenuated live ILTV vaccines are often used to help control disease, but these vaccines have well documented limitations, including retention of residual virulence, incomplete protection, transmission of vaccine virus to unvaccinated birds and reversion to high levels of virulence following bird-to-bird passage. Recently, two novel ILTV field strains (class 8 and 9 ILTV viruses) emerged in Australia due to natural recombination between two genotypically distinct commercial ILTV vaccines. These recombinant field strains became dominant field strains in important poultry producing areas. In Victoria, Australia, the recombinant class 9 virus largely displaced the previously predominant class 2 ILTV strain. The ability of ILTV vaccines to protect against challenge with the novel class 9 ILTV strain has not been studied. Here, the protection induced by direct (drinking-water) and indirect (contact) exposure to four different ILTV vaccines against challenge with class 9 ILTV in commercial broilers was studied. The vaccines significantly reduced, but did not prevent, challenge virus replication in vaccinated chickens. Only one vaccine significantly reduced the severity of tracheal pathology after direct drinking-water vaccination. The results indicate that the current vaccines can be used to help control class 9 ILTV, but also indicate that these vaccines have limitations that should be considered when designing and implementing disease control programs.

Highlights

Infectious laryngotracheitis (ILT) is a contagious upper respiratory tract disease of chickens that causes significant economic losses in poultry industries around the world [1,2,3]
The disease is caused by an alphaherpesvirus, infectious laryngotracheitis virus (ILTV), which is classified taxonomically as Gallidherpesvirus 1 [4]
Evidence from whole genome sequence analysis of the three vaccine strains in use in Australia, along with the genome of these newly emerged strains, confirmed that the class 8 and 9 strains emerged as a result of natural recombination between the recently introduced European-origin vaccine strain (Serva ILTV, MSD Animal Health) and the original Australian vaccine strains (SA-2 and A20 ILTV, Zoeitis) [13]

Summary

Introduction

Infectious laryngotracheitis (ILT) is a contagious upper respiratory tract disease of chickens that causes significant economic losses in poultry industries around the world [1,2,3]. The novel recombinant class 9 ILTV strain became the predominant field strain in important poultry producing regions in Victoria, Australia, largely displacing the previously dominant class 2 ILTVs [12] and continues to cause significant outbreaks of disease in commercial poultry flocks [13]. Recent studies have shown that, compared to class 2 ILTV, class 9 ILTV has enhanced replication kinetics, increased virulence and enhanced potential for horizontal transmission. These differences may help to explain the dominance of class 9 ILTV in the field [14]

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