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Title: Antigenic differences among NDV strains of different genotypes used in vaccine formulation affects viral shedding after a virulent challenge

Author
item Miller, Patti
item King, Daniel
item Afonso, Claudio
item Suarez, David

Submitted to: Vaccine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2007
Publication Date: 9/28/2007
Citation: Miller, P.J., King, D.J., Afonso, C.L., Suarez, D.L. 2007. Antigenic differences among NDV strains of different genotypes used in vaccine formulation affects viral shedding after a virulent challenge. Vaccine. 25:7238-7246.

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 in their ability to protect vaccinated birds from shedding virus after exposed to an outbreak virus. The birds vaccinated with a vaccine made from an isolate that was genetically similar to the recent outbreak viruses shed less virus in oral secretions than the birds vaccinated with vaccines made from viruses less similar to the outbreak virus. The vaccine that effectively reduced virus shed should also reduce virus transmission to other birds and thereby provide improved ND control.

Technical Abstract: Strains of Newcastle disease virus (NDV) can be separated into genotypes based on genome differences even though they are antigenically considered to be of a single serotype. It is widely recognized that an efficacious Newcastle disease (ND) vaccine made with any NDV does induce protection against morbidity and mortality from a virulent NDV challenge. However, those ND vaccines do not protect vaccinates from infection and viral shed from such a challenge. Vaccines prepared from ND viruses corresponding to five different genotypes were compared to determine if the phylogenetic distance between vaccine and challenge strain influences the protection induced and the amount of challenge virus shed. Six groups of four-week-old specific pathogen-free Leghorn chickens were given oil-adjuvanted vaccines prepared from one of five different inactivated ND viruses including strains B1, Ulster, CA02, Pigeon84, Alaska196, or an allantoic fluid control. Three weeks post-vaccination, serum was analyzed for antibody content using a hemagglutination inhibition assay against each of the vaccine antigens and a commercial NDV ELISA. After challenge with virulent CA02, the birds were examined daily for morbidity and mortality and were monitored at selected intervals for virus shedding. All vaccines except for the control induced greater than 90% protection to clinical disease and mortality. The vaccine homologous with the challenge virus reduced oral shedding significantly more than the heterologous vaccines. NDV vaccines formulated to be phylogenetically closer to potential outbreak viruses may provide better ND control by reducing virus transmission from infected birds.