Efficacy of a genotype 2 Newcastle disease vaccine (Avinew) against challenge with highly virulent genotypes 5d and 3d.

Since 2002, following its introduction, the lineage 5d Newcastle disease virus (so-called Goose paramyxovirus - GPMV) strain has caused numerous disease outbreaks among commercial and backyard poultry in South Africa, raising questions about the ability of commercially available Newcastle disease vaccines to fully protect poultry against the strain. This study aimed to determine whether there are differences in the level of protection offered by Avinew Newcastle disease vaccine against GPMV virus as compared with a 3d Newcastle disease virus isolated in South Africa in 1993 (Rainbow challenge virus - RCV) strain. Six groups of 10-day-old, specific pathogen-free chickens were vaccinated with doses of 10(3.0), 10(4.5) and 10(6.0) EID50 of Avinew vaccine and challenged at 4 weeks of age intramuscularly at a dose of 10(5.3) EID50/0.2 ml/bird of GPMV and RCV. No statistically significant difference could be found in the protection offered by Avinew vaccine against GPMV as compared to RCV challenge. The protection offered against the ND challenge was found to be dose dependent. At the recommended field dose of 10(6.0) EID50 the vaccine gave 100% protection from mortality against both the challenge viruses, but not against infection and replication of the viruses, as gross lesions were evident even in apparently healthy birds that survived the challenge. The protective dose (PD90) of the Avinew vaccine against GPMV challenge was calculated at 10(4.38) and against that of RCV at 10(4.43).