Controlling infectious laryngotracheitis (ILT) with vaccination is critical in maintaining healthy and profitable poultry production. Nearly all long-lived poultry in the US are vaccinated against ILT.
Commonly, a recombinant vaccine of the herpesvirus of turkey (HVT), fowlpox virus vectors, live attenuated vaccines of chicken-embryo origin (CEO) or tissue-culture viral-origin types are used, sometimes in combination.
“CEO vaccines produce the best protection by diminishing virus shedding, rapidly reducing the impact of disease outbreaks. However, these vaccines can potentially regain virulence, a drawback leading to performance penalties,” said Maricarmen Garcia, PhD, professor at the University of Georgia’s Poultry Diagnostic and Research Center.
Recombinant vaccines are a safer vaccination alternative against ILT because they do not become virulent during usage and thus can be safely administered in the hatchery. But their delayed immune response and inability to prevent viral shedding from the upper respiratory tract in the early stages of infection are reportedly significant limitations to their effectiveness.
“These findings underscore the need to find safer immunization strategies that can effectively deliver local T cells to sites of viral entry,” Garcia said.
Garcia and her research team hypothesized that administering ILT virus (ILTV) by vaccine-recombinant antigens via natural mucosal routes of viral entry may induce effective T-cell responses that can rapidly clear the virus and prevent more virus replication and shedding.
Study objectives
The researchers sought to demonstrate that a safe and cost-effective mucosal immunization strategy using adjuvanted DNA plasmids expressing known immunogenic ILTV glycoproteins delivered by calcium phosphate nanoparticles is effective.
The study had three specific aims:
- Clone three ILTV glycoproteins into high-expression plasmids for DNA vaccine formulation.
- Assess the safety of the newly formulated vaccine when administered via the ocular route.
- Assess the protection efficacy induced by the vaccine formulation after challenge with a virulent ILTV strain.
Results
Administration of the ILTV plasmids formulations did not affect the hatchability after in ovo immunizations. Also, in ovo and/or eye-drop immunizations did not affect bodyweight gain or induce any measurable clinical signs in specific-pathogen-free chickens.
Protection of plasmid-vaccinated groups after challenge showed that prime-boost administration of surface glycoproteins plasmid formulation via eye drop resulted in 91% survivability and presented a trend toward reduced clinical-sign scores of ILT after challenge. However, administering the glycoprotein plasmid formulation via eye drop to HVT-Newcastle disease (ND)-laryngotracheitis (LT) in ovo-vaccinated chickens did not enhance the HVT-ND-LT protection.
For chickens that received a single or double dose of surface ILTV glycoproteins or cytosolic antigen plasmid formulations in ovo and/or at 1 day of age, survivability ranged from 53% to 67%, with no visible trends toward reduced clinical signs of the disease.
Together, these results highlighted the importance of boost immunization to enhance the effectiveness of DNA immunizations. Neither route of administration (in ovo or eye drop), age, dose (single or double) or prime-boost strategies of plasmid administration induced a reduction of challenge-virus replication.
Future research will be directed to complement plasmid formulations with immunomodulants and adjuvants that enhance the induction of local immune responses.
“This project demonstrated the safety of the plasmid formulations for in ovo and eye-drop administration. It also showed that ILTV plasmid-based immunizations were effective in avoiding ILT-induced mortality and reducing clinical signs of the disease in a prime-boost immunization strategy via eye drop,” Garcia concluded.
The research was funded by USPOULTRY and the USPOULTRY Foundation, thanks in part to Fieldale Farms Corporation. Click here to view the industry summary.
Editor’s note: Content on Modern Poultry’s Industry Insights pages is provided and/or commissioned by our sponsors, who assume full responsibility for its accuracy and compliance.
