Submitted to: Avian Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/30/2008
Publication Date: 6/1/2008
Citation: Perozo, F., Villegas, P., Dolz, R., Afonso, C.L., Purvis, L.B. 2008. The VG/GA strain of Newcastle disease virus: Mucosal immunity, protection against lethal challenge and molecular analysis. Avian Pathology. 37(3):237-245. Interpretive Summary: This study is a comparison of the properties of two widely used Newcastle Disease Viruses live attenuated vaccines, the VG/GA strain and the LaSota strain. While both vaccines have proven to be highly effective against challenges, differences in virus distribution and production of antibodies was observed, with higher intestinal IgA levels for the VG/GA strain. Genomic differences observed at the nucleotide levels may explain the different properties of these viruses.
Technical Abstract: The VG/GA strain of Newcastle disease virus (NDV) isolated from the intestine of healthy turkeys has been proposed to replicate in the respiratory and intestinal tract of chickens. In this study, the virus distribution, the mucosal and systemic immune response, the efficacy against lethal challenge and the full genome sequence of the VG/GA strain were compared with LaSota strain of NDV. The VG/GA strain was detected at different time points in the respiratory and intestinal tract of chickens with a preferential tropism for the latter. Both the VG/GA and LaSota strains induced NDV specific immunoglobulin A (IgA) at the upper respiratory tract. IgA levels were higher in the trachea for LaSota strain, while they were higher in the intestine for the VG/GA strain. Positive correlation between virus distribution of the viruses and IgA production observed. Despite the presence of the maternal antibodies in broilers, early vaccination with the VG/GA strain afforded 95 to 100% protection against lethal challenge, equivalent to the protection conferred by LaSota strain. Full genome sequence analysis classified the VG/GA strain within class II, genotype II viruses, which also include most of the respirotropic vaccine strains. Differences with the LaSota strain were observed at the nucleotide and amino acid levels. The differences in proteins associated was with receptor recognition and fusion may explain the differential phenotype of the VG/GA; however, verification of the significance of those changes is required. Taken together, these results validate field observations on the efficacy of VG/GA vaccination and demonstrated the unique characteristics of the strain.