Genotype VII.1.1-Based Newcastle Disease Virus Vaccines Afford Better Protection against Field Isolates in Commercial Broiler Chickens

Abstract

This study evaluated the efficacy of live and inactivated conventional GII LaSota and recombinant GVII Newcastle disease vaccines in commercial broilers. The experimental groups (G2-G7) were vaccinated on day 7 and day 21 of age with live vaccines from the same vaccine type "GII LaSota, GVII vaccine (A), GVII vaccine (B)" via eye drop; however, G3, G5, and G7 received a single dose from inactivated counterpart vaccines subcutaneously on day 7 of age. Vaccine efficacy was evaluated based on elicited humoral immunity, clinical protection, and reduction in virus shedding after challenge with virulent GVII 1.1. strain. Results demonstrated that live and inactivated recombinant GVII vaccine based on VG/GA strain backbone elicited superior protection parameters (100% protection). Although the conventional GII LaSota live and inactivated vaccination regime protected 93.3% of vaccinated birds, the virus shedding continued until 10 DPC. The post-vaccination serological monitoring was consistent with protection results. The study concludes that conventional GII ND vaccines alone are probably insufficient due to the current epidemiology of the GVII 1.1 NDV strains. Our findings further support that protection induced by recombinant GVII 1.1. ND vaccines are superior. Interestingly, the efficacy of recombinant ND vaccines seemed to be influenced by the backbone virus since the VG/GA backbone-based vaccine provided better protection and reduced virus shedding.

Keywords: Newcastle disease; VG/GA; broiler chickens; genotype VII.1.1; recombinant vaccine.

Figure 1

Survival of vaccinated groups post challenge with virulent genotype VII.1.1. Newcastle Disease Virus. (A) GII LaSota vaccinated group. (B) Vaccine (A) GVII vaccinated group. (C) Vaccine (B) GVII vaccinated group. Abbreviations; GII: genotype II-based vaccine, GVII: genotype VII.1.1.-based vaccine, L/L: live vaccine at 7 and 21 days, LI/L: live and inactivated at 7 days, then live vaccine at 21 days.

Figure 1

Survival of vaccinated groups post challenge with virulent genotype VII.1.1. Newcastle Disease Virus. (A) GII LaSota vaccinated group. (B) Vaccine (A) GVII vaccinated group. (C) Vaccine (B) GVII vaccinated group. Abbreviations; GII: genotype II-based vaccine, GVII: genotype VII.1.1.-based vaccine, L/L: live vaccine at 7 and 21 days, LI/L: live and inactivated at 7 days, then live vaccine at 21 days.

Figure 2

Trachea in vaccinated and control groups chicks at 3 days post challenge (H & E stain, ×100), showing the negative control normal histopathological architecture of the trachea (A). The challenge control (E). All vaccinated group’s (D,H) tracheal structures were as in the normal group except for the LaSota GII LI\L (B,F) and the vaccine-B GVII L/L (C,G) groups. Abbreviations: GII: genotype II-based vaccine, GVII: genotype VII.1.1.-based vaccine, L/L: live vaccine at 7 and 21 days, LI/L: live and inactivated at 7 days, then live vaccine at 21 days.

Figure 3

Trachea in vaccinated and control groups chicks at 7 days post challenge (H & E stain, ×100), showing the normal histopathological architecture of trachea with few lymphocytes in the submucosa and between mucosal epithelium in the negative control group (arrows) (A). The challenge control group showed severe deterioration of the tracheal structure and tracheal casts (star) (E). All vaccinated groups (B,D,G,H) had reduced tracheal mucosa damage, except for the vaccine-B GVII L/L (C) and the LaSota GII LI\L (F) groups. Abbreviations: GII: genotype II-based vaccine, GVII: genotype VII.1.1.-based vaccine, L/L: live vaccine at 7 and 21 days, LI/L: live and inactivated at 7 days, then live vaccine at 21 days.