Development of avian paramyxovirus 3 as a vaccine vector against infectious bursal disease in one-day-old specific pathogen free chickens

ABSTRACTInfectious bursal disease (IBD) is an acute, highly contagious, immunosuppressive disease affecting young chickens, resulting in substantial economic losses to the poultry industry worldwide. Although strict hygienic measures and various vaccination strategies have been adopted, IBD remains a major problem for the poultry industry. The economic significance of this disease is exhibited in two ways. First, the disease can cause high morbidity and mortality. Second, severe prolonged immunosuppression of chickens when infected at an early age leads to susceptibility to other diseases and vaccination failure. Therefore, chicks should be protected from early infection, usually achieved by vaccinating breeder flocks and active immunization of the newly hatched chicks. Vaccines include live-attenuated, viral vectored recombinant, subunit, and inactivated vaccines currently available to control infectious bursal disease (IBD). The major flaws of available vaccines are the reversion to virulence, the generation of new variant viruses, inability to replicate in the presence of maternal antibodies, lack of proper delivery systems, recombination and integration into the host genome, and inadequate systemic immune response. To overcome these obstacles, we have evaluated avian paramyxoviruses (APMVs) as vaccine vectors to generate vaccines against IBD. In the present study, we constructed recombinant Newcastle disease virus (NDV) strain LaSota (rLaSota/VP2) and recombinant avian paramyxovirus-3 (APMV-3) strain Netherlands expressing VP2 protein (rAPMV-3/VP2), the immunogenic protein of IBDV, and to evaluate their protective efficacies following immunization of one-day-old specific pathogen-free (SPF) chicks. Our results showed that both recombinant viruses stably express the VP2 protein, and their in vitro growth characteristics were almost similar to their respective parental viruses. Immunization of one-day-old SPF chicks demonstrated that rAPMV-3/VP2 protein elicited IBDV specific neutralizing antibodies and provided complete protection against the IBDV STC challenge. In addition, the rAPMV-3/VP2 protects chickens from clinical signs, gross lesions, and histopathology even at lower vaccine doses. Moreover, rAPMV-3/VP2 provides slightly better protection than the commercial vaccine from histopathology lesion against IBD at four weeks of age. This study suggests that recombinant APMV-3 expressing VP2 protein could be used as a potential vaccine against IBD in field conditions where maternal antibodies exist.