QX not the only IBV strain of concern to poultry producers
The QX strain of infectious bronchitis virus (IBV) remains prevalent throughout Europe, Africa and the Middle East, but it isn’t the only strain of IBV that producers need to worry about.
“IBV is a moving target” because the virus changes, most likely due to spontaneous mutation or genetic recombination, said Luuk Stooker, DVM, a technical manager for Zoetis.
J.J. (Sjaak) de Wit, DVM, PhD, senior scientist, GD Animal Health Service, the Netherlands, agreed and said that an increasing number of countries have to deal with an increasing number of variants. “Some variants stay for a longer time, and others come and go.”
Stooker and de Wit agreed the best approach to managing IBV is the use of a homologous vaccine against the strain of IBV that is circulating. When a homologous vaccine isn’t available, a combination of heterologous vaccines can provide much better, though not full, protection compared to using a single heterologous vaccine, they said during a Watt Global Media webinar sponsored by Zoetis.
They both cited examples of how different vaccine combinations can provide different levels of cross-protection. Controlled challenge studies, for instance, have demonstrated that the combination of a live IB primer on day-of-age followed two weeks later by an IB QX vaccine gives “strong to very strong cross-protection” against IB 793B Italy 02 and Variant 2, Stooker said.
de Wit noted that for layers and breeders, “a good, live priming is essential before boosting with an inactivated vaccine.”
He emphasized that determining the best vaccination program requires high-quality IBV diagnostics to identify predominant strains. Typing systems such as serotyping and genotyping are screening methods used to detect potential variants, but they do not determine the level of cross-protection by a vaccine.
Genetic homology between a vaccine and field strain can vary from 40% to 100%, and the only way to determine which combination of vaccines will provide the best protection is by conducting challenge studies, which are “expensive but essential,” he said.
Stooker said that IBV vaccination programs should be based on identification of circulating strains and their risk for causing disease. “Don’t wait until outbreaks occur,” he cautioned.
Application method crucial
de Wit said that application procedures for IB vaccines can dramatically affect efficacy. Spray-on vaccination is better than water administration. “With spray it’s in the respiratory tract where it needs to be; with drinking water, it’s not.”
IB vaccines sprayed on will yield better results if ventilation is turned off but the lights are on, de Wit continued. He also advised using cold water for reconstituting vaccines and said that a second IB vaccine should not be administered sooner than 2 weeks after the first IB vaccine is given.
In response to a question about serology for monitoring the success of IB vaccination in broilers, de Wit said that the serological response will be very low on both the hemagglutination inhibition or ELISA tests, especially in young birds.
 Stooker L, et al. Cross-protection capabilities of a combined vaccination program containing two live IBV vaccines against today’s most relevant field strains in the Europe, Africa and Middle East Region. 8thSymposium on ACOV & AMPV/2nd Meeting Cost Action 1207, Rauischholzhausen, Germany, June 2014.