Innovax-ILT used extensively in US commercial layers

The recombinant infectious laryngotracheitis (ILT) vaccine Innovax-ILT is now being used extensively in commercial layers, Dr. Keith Honegger said at the recent International Avian Respiratory Disease Conference in Athens, Georgia.

Since its introduction in 2007, hundreds of millions of layers have received Innovax-ILT and the results have been excellent, said Honegger, a veterinarian with Merck Animal Health, developer of the Innovax vaccines. “We’re seeing improved livability and a slight improvement in egg production,” he added.

The backbone of Innovax-ILT is the herpesvirus of turkey (HVT), which provides a carrier for ILT genes that initiate immunity against ILT; HVT is known to be safe for chickens and also protects against Marek’s disease, he said.

The vaccine requires only one dose, which is administered subcutaneously to 1-day-of-age commercial layer chicks. Innovax-ILT can also be given in ovo to 18-day embryos. In contrast, the use of chicken-embryo-origin (CEO) vaccines on large layer farms with multiple-age houses and a serious ILT threat requires vaccination at a young age, such as 6 or 7 weeks, followed by field vaccination at 10 to 15 weeks. This protocol increases stress on birds as well as labor costs, he explained.

UNIVERSITY FIELD TRIAL

In a trial conducted by Purdue University, investigators administered an ILT challenge (USDA strain) to 42-week-old commercial layer chickens that were vaccinated with Innovax-ILT at 1 day of age in a commercial hatchery and raised in field conditions, Honegger continued. Unvaccinated, specific-pathogen-free (SPF) birds were used as challenge controls.

Almost all control birds developed clinical signs of ILT compared to only one case of minimal eye irritation among vaccinated birds, the veterinarian reported. In addition, ILT virus was isolated from all control birds tested, compared to only one of 10 vaccinated birds, Honegger said (Table 1).

“Vaccines do not prevent birds or any other species from contracting a disease, but they can greatly minimize the clinical signs and consequences,” he added, noting that the main consequence of ILT infection in unvaccinated layer flocks is high mortality.

Unlike some CEO vaccines, however, which can cause ILT, birds vaccinated with Innovax-ILT have shown no side effects. Furthermore, vaccinated flocks have not experienced latent ILT, carrier states or rolling reactions, he said.

Honegger emphasized that vaccine handling and administration is crucial to achieve the best protection with Innovax-ILT; birds that are missed during the vaccination process are not protected against ILT.

The veterinarian also cautioned that vaccine efficacy could be reduced if there is an excessive and/or early ILT challenge from a “hot” ILT virus. Reduced dosage of the vaccine or adding an excessive amount of Garasol (gentamicin sulfate) to the Marek’s diluent also could reduce vaccine effectiveness. In addition, HVT recombinant vaccines should not be administered with another HVT vaccine.

60 -WEEK DURATION OF IMMUNITY

In a separate presentation at the conference, a study was presented that demonstrated the duration of immunity for Innovax-ILT is at least 60 weeks.

Investigators subcutaneously vaccinated 1-day-old SPF chicks with Innovax-ILT and then at 10-week intervals administered an intratracheal challenge with a virulent ILT virus up to 60 weeks of age. They observed the birds daily for 10 days after each challenge and chickens were considered negative if they remained free of ILT clinical signs.

At each challenge period, 90% to 100% of unvaccinated controls developed clinical signs or died, which validated the virulence of the ILT challenge.

Percent protection against ILT in vaccinated birds ranged from 90% to 100% and was 94% at 60 weeks, said Lillian Melson and colleague Karen Jensen, of Merck Animal Health.

For more on Innovax-ILT and other products in the Innovax line, go to innovax-vaccines.com.