A producer’s ability to match vaccine coverage to the circulating infectious-bronchitis threat depends largely on a well-executed surveillance program, according to Mark Jackwood, PhD, University of Georgia.
He said producers often take a “shoot-in-the-dark” approach with IB. “They starting adding IB strains into their vaccination program hoping for cross-protection without really knowing which strains are in their flocks,” Jackwood told Poultry Health Today.
Research has shown that IB vaccines don’t directly interfere with one another, but when four or more strains are used in combination, the available antigen mass can be diluted to the point where birds don’t have a robust immune response.
Vaccines with multiple strains produced by pharmaceutical companies are pre-tested for antigen response, Jackwood said. Still, employing a vaccine program with more than three strains for extended cross protection could be asking for trouble.
“The real problem begins when producers start adding a third or even fourth IB strain from another manufacturer. These additions dilute all the antigens to the point where birds can’t develop a strong immune response to any of the strains,” he explained.
According to Jackwood, surveillance programs need to look at the last year’s IB strains and begin early monitoring in the August through October time frame to assess new disease pressure.
“The only way to know what is really going on in the barn is to take nasal swabs and get them tested in the laboratory for serotypes,” he said. Today’s IB testing is rapid, real-time PCR testing allowing the lab to run a large number of samples in a timely, cost effective manner.
Sentinel birds are another useful option when birds remain sick despite IB vaccination.
“We vaccinate sentinel birds with known circulating viruses, let them develop immunity and then place them in the flock. When we remove them at the optimum time frame of 10 and 20 days for virus infection, we’re identify the pathogenic virus that’s been hiding under the surface,” he explained.
Producers are urged to actively test for circulating strains and not just use a vaccine based on history. IB pressure is different every year and a good surveillance program helps correctly identify the circulating strains.
Properly vaccinating birds ensures a good antigen response. “Make sure your vaccination machines are in good working order, that the vaccine and diluent are kept cold and each bird gets an adequate dose of the vaccine. Most importantly, don’t cut the dose,” Jackwood said.
For producers in antibiotic-free programs, secondary infections from Escherichia coli pose a greater threat. As a virus, IB remains a treatable pathogen but any damage from IB can open the door for damaging E. coli bacterial infection.
“We see the primary challenge from IB but without the antibiotic tools to fight the secondary E. coli infection, the birds will be much sicker with increased losses due to airsacculitis and higher numbers of condemnations at the processing plant,” Jackwood explained.