Comparison of viral shedding following vaccination with inactivated and live Newcastle disease vaccines formulated with wild-type and recombinant viruses

Authors: Miller, Patti; Estevez, Carlos; Yu, Qingzhong; Suarez, David; King, Daniel

Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2008
Publication Date: 3/25/2009
Citation: Miller, P.J., Estevez, C., Yu, Q., Suarez, D.L., King, D.J. 2009. Comparison of viral shedding following vaccination with inactivated and live Newcastle disease vaccines formulated with wild-type and recombinant viruses. Avian Diseases. 53:39-49.

Interpretive Summary: Newcastle disease (ND) is a major viral disease of poultry that occurs worldwide and is known in the U.S. as exotic ND. Outbreaks of ND lead to financial losses from the deaths of the birds infected with the ND virus (NDV), from having to cull infected and likely infected birds to control the spread of the virus and from restrictions on export of poultry and poultry products from the region of the outbreak. Current ND vaccines when given correctly protect infected birds from dying or getting sick, but they do not protect vaccinated birds from shedding the outbreak virus to other birds. The current vaccines are made with older strains of NDV that differ genetically from the strains that have caused recent outbreaks. The goal of our research was to improve the ability of ND vaccines to protect vaccinated birds from shedding NDV. We compared ND vaccines of different genetic lineages in their ability to reduce the amount of virulent challenge virus shed from vaccinated birds after they were challenged with either a recent outbreak virus or the current 9CFR challenge virus. The birds vaccinated with vaccines made from an isolate that was genetically similar to the challenge virus used shed less virus in oral secretions than the birds vaccinated with vaccines made from viruses less similar to the challenge virus. A vaccine that effectively reduced virus shed should also reduce virus transmission to other birds. Matching the vaccine administered to the genotype of either the virulent viruses known to be circulating in that area or to the most likely outbreak virus for that area could be used to improve ND control.

Technical Abstract: Virulent Newcastle disease virus isolates from recent outbreaks are the same serotype but a different genotype than current vaccine strains. Prior experiments with inactivated vaccines in chickens show significantly less virus shed in birds vaccinated with a homologous vaccine (same genotype as challenge) compared to chickens vaccinated with genotypically heterologous vaccines. Subsequent experiments have compared the protection induced in chickens by live vaccines of B1 and LaSota (genotype II), Ulster (genotype I), and recombinant viruses that express the hemagglutinin-neuraminidase (HN) gene or the HN and fusion (F) genes of CA 2002 (genotype V). Vaccinates were challenged with virulent viruses, CA 2002 (genotype V) or Texas GB (TXGB, genotype II). After challenge with CA 2002 the birds vaccinated with a live recombinant genotype V virus containing the HN of CA 2002 shed significantly less virus in oropharyngeal swabs compared to B1 and had fewer birds shedding virus compared to B1, LaSota and Ulster vaccinates. After challenge with CA 2002 birds vaccinated with the recombinant containing both the F and HN of CA 2002 (rA-CAFHN) shed less virus and fewer birds shed virus compared to LaSota-vaccinated birds. TXGB-challenged LaSota-vaccinated birds shed less virus and fewer birds were shedding virus compared to TXGB-challenged rA-CAFHN-vaccinated birds. Genotypic differences between vaccine and challenge did not diminish ability of vaccines to protect against disease, but genotypic similarity did reduce virus shed and may reduce transmission. The development and use of vaccines of the same genotype as the expected field challenge may provide an additional tool for control of this important poultry pathogen.