Undercover: ILT vaccine choice a ‘no brainer’ for major producer

Infectious laryngotracheitis (ILT) was “hot” and worrisome in several areas where a major layer producer had flocks, and the conventional means of vaccinating wasn’t working.*

Even with a triple dose of live, chicken-embryo- origin (CEO) vaccine, mortality during the most serious outbreaks was running 5% to 10%, a manager at the company’s northeastern facility said at a seminar held recently in Ontario.

“We just weren’t getting control of ILT and ended up creating a more serious issue by re-infecting everything again with the CEO vaccine virus,” he said.

Forced to consider other options, the company decided to investigate use of the recombinant herpesvirus of turkey (HVT) vaccine, Innovax-ILT. But if Innovax-ILT was selected, then a recombinant HVT Gumboro vaccine couldn’t be used.

Dr. Linnea Newman, a technical service veterinarian with Intervet/Schering-Plough Animal Health, sponsor of the seminar, explained that field experience and lab studies indicate that any recombinant vaccine that contains HVT should not be administered with another HVT vaccine — recombinant or not — because protection won’t be optimal. Exactly why isn’t known.

For the layer producer, the decision about which recombinant HVT vaccine to use was “a no brainer,” with the ILT vaccine clearly the better pick.

The reasoning behind the decision was straightforward. “We can control Gumboro by vaccinating early with a live vaccine, but ILT is a more serious threat,” he said.

MORTALITY DECLINED

Since the company started using Innovax-ILT at its northeastern facility, mortality from ILT has declined to about 0.5% to 1% and surviving chicks perform well.

“If the vaccine is correctly administered, it’s going to work...we don’t plan on getting off of it anytime soon,” he said, noting that the vaccine is administered subcutaneously at the hatchery to day-old chicks.

The vaccine has other advantages: It requires only one dose, which is “too good to be true,” and it eliminates the need for field ILT vaccination, he added. “That’s one less crew coming, which is good for biosecurity, as well as labor savings.”

‘SMART CHOICE’

Newman called it a “smart choice” to use the recombinant vaccine for ILT control and a live vaccine for control of Gumboro, formally known as infectious bursal disease (IBD).

“We need to vaccinate for both ILT and IBD. But ILT is a lifelong threat to flocks that comes with high mortality and high cost — and one that could potentially spread and cause trouble for your neighbors if you move your pullets or have visitors at the farm,” she said.

IBD is a threat in layers only until sexual maturity. In addition, live IBD vaccines do not produce harmful reactions in vaccinated flocks or adjacent houses, nor do they produce a carrier state within the bird or interfere with vaccination for Newcastle disease (ND) or infectious bronchitis (IB), Newman said.

Unlike a live CEO-ILT vaccine, the recombinant ILT vaccine causes no side effects, doesn’t spread in the field and can be administered with ND or IB vaccines without causing interference, she said.

ADDITIONAL MD PROTECTION

The HVT in Innovax-ILT, Newman continued, serves as a carrier for an ILT gene that initiates immunity against ILT, and it also protects against Marek’s disease (MD). If flocks need protection against very virulent MD (vvMD), Innovax-ILT can be administered with a Rispens vaccine such as Rismavac, which does not contain HVT, she said.

Dr. Keith Honegger, technical service manager with Intervet/Schering-Plough Animal Health, cited shedder trials, which simulate natural disease exposure. Chicks vaccinated with Innovax-ILT plus Rismavac had excellent protection against vvMD, as determined by lesion scoring and mortality, compared to unvaccinated controls.

In efficacy studies, chicks were vaccinated subcutaneously at 1 day of age with Innovax-ILT, then challenged at 4 weeks of age with three prevalent ILT viruses. The birds were protected against all three ILT viruses. “Full immunity to ILT is achieved at about 4 weeks of age,” he said.

To get the best results with Innovax-ILT, the vaccine must be administered properly. Since the vaccine virus does not spread from chick to chick like a CEO vaccine virus, any chicks that are missed upon vaccination will not be protected, Honegger cautioned.

Newman noted that Innovax-ILT is credited with controlling a serious 2009 ILT outbreak among broiler flocks in Canada. No ILT outbreaks have occurred in flocks correctly vaccinated with the vaccine. Currently, Canadian breeder and layer producers are encouraged to use Innovax-ILT and may supplement with a live ILT vaccine via eye-drop for early protection or to ensure 100% coverage.

*Editor’s note: The unattributed information in this article was provided by a major US layer producer on the condition that its name and location be kept confidential. The producer has, however, reviewed the information for technical accuracy and approved it for publication in Layer Health.

On histology, intranuclear inclusion bodies and syncytia typical of ILTV infection. Photo courtesy of Dr. Guillermo Zavala, University of Georgia.