Novel European approach to IB control explored for US broilers

A novel strategy for controlling infectious bronchitis (IB) that’s been effective abroad may be on the horizon for US producers struggling with the disease in their broiler flocks.

The approach is based on the use of serotypes, or subspecies, of the IB virus and is being spearheaded by Mark Jackwood, PhD, a molecular virologist at the University of Georgia.

Speaking at an IB symposium held recently at the XVIII World Veterinary Poultry Congress, Jackwood said it’s well known that if only one virus in an IB vaccine is administered, birds will be protected against that particular virus.

However, he added, some IB serotypes have cross-protective ability against other IB serotypes — a phenomenon that scientists call “Protectotype.” In addition, when two different IB serotypes are used, birds will develop immunity to those serotypes and also develop cross-reacting antibodies to some of the other IB serotypes. “We get a broader type of protection,” Jackwood said.

LESS COSTLY

An approach toward IB control involving Protectotype is largely based on work by Jane Cook, PhD, a microbiologist in the UK and recognized authority on IB. She points out that IB variants arise frequently and that Protectotype is less costly and makes more sense than developing a new vaccine for every variant that arises. Even though the IB virus is capable of frequent mutations, she says, the genetic makeup of the virus changes only minimally and the rest remains the same, which is why some IB serotypes are able to provide cross-protection.

In Europe and elsewhere, research and field experience have demonstrated that using an IB vaccine based on the Massachusetts serotype followed by one based on the IB variant 4/91 — a common variant in Europe — can provide broad protection against many IB variants.

A case in point would be experience with 25 million broilers on two Middle Eastern farms owned by two different companies. Broilers on both farms had respiratory signs of IB as well as kidney damage; there were serious declines in bodyweight due to IB and high mortality. One farm had been using only a Ma5 vaccine and the other was using an H120 IB vaccine.

A strategy involving Protectotype was initiated, involving administration of Nobilis IB Ma5, then Nobilis IB 4/91 — a vaccine based on a different serotype than Ma5 — followed by Nobilis IB Ma5 plus a Newcastle disease (ND) vaccine since ND was also a problem. Mortality on both farms declined, bodyweight improved and days until slaughter declined.

More specifically, mortality on one farm dropped from 30% to 6%. On the other farm, mortality dropped from 35% to less than 8% after just two cycles of the new strategy involving Protectotype; bodyweight increased from 1.406 grams to 1.600 grams — nearly 14% — and days until slaughter decreased from 36.05 to 34 days (Journal of Respiratory Protection Issue 1, page 10).

SUBSTITUTE STRAIN FOR US

In his presentation, Jackwood said, “We don’t have 4/91 in the US and it’s not permitted here for good reason; the major problem we have is the Arkansas IB strain. We’re asking what can we substitute for 4/91?”

Toward this end, Jackwood spent a week in Europe with Sjaak De Wit, DVM, PhD, at the Animal Health Service, Deventer, the Netherlands. “We vaccinated specificpathogen- free birds with Ma5 on 1 day of age and with 4/91 at 14 days of age, then challenged birds with the US Arkansas or Georgia 98 IB strains,” he continued.

Five days after challenge, birds that had received both the Ma5 and 4/91 vaccines had about 90% protection against the Arkansas IB challenge, and there was 86% protection against challenge with the Georgia 98 strain, which is a Delaware-type virus, he said (Table 1).

In birds vaccinated only with Ma5, protection against the Arkansas IB challenge was also determined to be about 90%; this was higher than expected, but as it turned out, the challenge was weaker than intended. As expected, protection against the Georgia 98 IB challenge was only about 37% in birds that received only Ma5, Jackwood continued.

Protection was determined by scoring ciliary activity in the tracheal epithelium, he noted.

DELAWARE 072?

For the US market, Jackwood and colleagues are going to try substituting IB 4/91 with the Delaware 072 IB strain because it is distant and may provide a broader set of antibodies. The studies are underway, and Jackwood hopes to have data to share in the near future.

Jackwood explained that this work involves determining genetic similarities between viruses, particularly regarding a spike protein on the outside of viruses, and virus neutralization testing. “The spike protein is the one that induces neutralizing antibodies,” he said. “If we get an amino acid sequence similarity between spike genes in the high-80% or low-90% range, there will usually be some cross-protection.”

The researchers are also carefully examining the significance of ciliostatis scores and want to find out if protection against ciliostasis correlates with protection in the field. “We know it does in Europe; we want to see if the same holds true here with US IB viruses,” he said.

Jackwood is confident that progress can be made. In an interview, he said, “We already have a lot of really good vaccines available to us. I think that we can do a better job of actually applying those vaccines and getting a little broader protection using a protocol involving Protectotype.”

"We also know that this virus can have a high mutation rate." - Mark Jackwood PhD