Infectious bronchitis: Containing an ever-changing disease
By Dieter Vancraeynest, DVM, PhD
Infectious bronchitis virus (IBV) remains an important disease in broilers that impairs animal welfare and productivity. It’s also one of the most frustrating diseases to deal with because it’s ever-changing due to spontaneous mutation or genetic recombination.
Thanks to molecular technology and epidemiology, we can track the IBV strains that are predominant. We know that in Europe and South Africa, IBV QX is predominant, while in the Middle East, the predominant strain is IBV Variant 02. We still pick up IBV 793B in several countries, but many, though not all, are likely to be a vaccine strain.1
Despite this information, the situation is still far from black and white. There’s often more than one IBV strain circulating on a broiler farm. Further complicating the situation is the lack of cross-protection among some IBV strains. These facts make devising an effective vaccination plan difficult.
Monitoring is key
What’s certain regarding IBV is that there’s no cookie-cutter approach to vaccination that’s going to work on every broiler farm. An individualized strategy is necessary.
The best way to start getting a handle on the situation is by routine monitoring to see if IBV is circulating, especially since the disease is so common in broiler flocks. Monitoring is key. The risks of not monitoring can easily outweigh the costs of monitoring if it leads to an effective vaccination program that helps prevent major production losses due to IBV. Monitoring can also prevent producers from shooting in the dark — instituting a vaccination plan that doesn’t work and can be a waste of time and money.
Serological testing — the ELISA — is a good first test. It’s quick and inexpensive, but it won’t identify the strain or strains of IBV. It’s also possible that with ELISA, IBV infection can be missed because seroconversion takes time, and birds might go to market before the infection can be detected by ELISA.
Consequently, after sending a flock to market, some producers will retain 10 to 20 birds; blood can be drawn at the end of 2 weeks to see if late IBV infection indeed took place. Needless to say, it’s risky to keep sick birds around because they could shed virus and expose future flocks, so birds retained for testing must be kept as far away from a commercial farm as possible and handled by someone not visiting your broiler farms.
When an ELISA test is positive for IBV, the next best test is polymerase chain reaction (PCR) — ideally RT-qPCR, which stands for quantitative reverse transcription. It’s an excellent tool and helps pinpoint the IBV strains that are circulating. In some areas its use is limited due to availability or cost, but generally speaking it’s becoming more available and — as with many technologies — the cost will likely further come down. Just one PCR test may not make it possible to draw absolute, definitive conclusions about the IBV strains circulating, but it can provide really valuable information regarding the choice of vaccines.
The hemagglutination inhibition test is sometimes used to try and type different IBV strains, but cross-reaction between strains can occur, which makes interpretation of the results difficult. That’s why PCR testing is my first choice whenever possible for identifying circulating IBV strains.
An ideal plan
In an ideal world, PCR testing would lead to a vaccination plan that would be tested in challenge studies. This is because genetic homology — genetic similarity — can vary between vaccine and field strains. Challenge studies are the only way to be certain that a particular vaccine protocol is likely to be effective.
In challenge studies, specific-pathogen-free chickens are vaccinated with the proposed vaccination protocol, then are challenged with field isolates of IBV obtained from the farm where future flocks would receive the proposed vaccination protocol. These studies, however, are time-consuming and expensive, and therefore cannot be commonly conducted.
When challenge studies aren’t possible, the best approach for broilers confronted with IBV is the use of a homologous vaccine — a vaccine based on the same strain or serotype of the predominant IBV that’s circulating. The addition of a live IBV Massachusetts combination primer helps broaden protection.2 When the IBV QX strain is predominant, that would mean combining a live IBV Massachusetts vaccine and the live IBV QX vaccine.
When a homologous vaccine isn’t available, a combination of heterologous vaccines is probably the best choice. Heterologous vaccines are those based on strains or serotypes that are different from the circulating IBV strains. Using more than one helps broaden protection.3
An example of the benefits monitoring can provide is the experience in Benelux and Germany. No one in 2004 had even heard of IBV QX. PCR monitoring was not being performed very often, and IBV wasn’t particularly linked to bad performance in flocks since no classical signs of IBV were seen. IBV QX was, in fact, causing subclinical disease in some cases and was building up pressure that eventually led to serious clinical outbreaks.4 It took some time to put all the pieces of the puzzle together. In the meantime, producers sustained huge financial losses.5 This experience underscores the importance of monitoring, which could have helped prevent or at least contain those losses suffered by producers.
It should go without saying that monitoring and a well-planned vaccination program must be coupled with good general management. This includes a solid biosecurity program, optimal housing conditions and control of other diseases, especially those that predispose birds to immunosuppression. When all these measures are taken, it is possible to help prevent or contain IBV infections and minimize losses from this pesky virus.
1 Franzo G, et al. Continued use of IBV 793B vaccine needs reassessment after its withdrawal led to the genotype’s disappearance. Vaccine. 2014 Nov 28;32(50):6765-7.
2 de Wit JJ, et al. Infectious bronchitis virus variants: a review of the history, current situation and control measures. Avian Pathology (June 2011) 40(3), 223-235.
4 Personal communication, Luuk Stooker, DVM.
Editor’s note: The opinions and recommendations presented in this article are the author’s and are not necessarily shared by the editors of Poultry Health Today or its sponsor.
Posted on January 22, 2017