Newcastle Disease Virus Vaccines Based On Genotype VII Strains Provide Efficient Protection Against Challenge With Circulating Very Virulent Field Virus (Genotype VII) In Broiler Chickens

Abstract

Newcastle disease virus (NDV) outbreaks still occur and cause disastrous economic losses in broiler chickens despite intensive vaccination policies using genetically different vaccines from the circulating strains. This study aimed to compare protection conferred by different vaccination strategies using genotype matched (genotype VII) and mismatched vaccine (genotype I and II) against challenge with currently circulating viruses in broiler chickens. 175 one- day-old broiler chicks were divided in to 5 groups. Groups 1 to 4 (G1, G2, G3 and G4) were vaccinated using genotype I (Ulster 2C strain), genotype II (VG/GA strain) and genotype VII (KBNP-4152R2L strain) vaccines according to manufacturer's instructions and group 5 (G5) was kept as control. Protection assessed based on clinical protection, seroconversion, shedding and histopathology.Chickens vaccinated with live genotype II vaccine at 7 and 21 days of age and killed genotype VII vaccine at 7 days of age (G2) were completely protected clinically with no mortality compared with control non vaccinated chickens (G5) that showed typical NDV clinical picture with (100%) mortality. while, other vaccinated groups showed lower level of clinical protection with (2.8%) mortality for each group. Viral shedding was greatly reduced in groups vaccinated with inactivated recombinant genotype VII vaccine (G2 and G3) which recorded (0% & 0%) and (16.6% & 0%) at 7 & 10 days post challenge, respectively compared with groups vaccinated with inactivated genotype II vaccine (G1 and G4) regardless the genotype of the combined live vaccine (either genotype II or VII). Moreover, histopathology of control non vaccinated challenged group (G5) revealed severe lymphocytic depletion and necrosis, epithelial degeneration beside neurological lesions. It was concluded that using genotype matched NDV vaccine with the currently circulating field strains can provide adequate clinical protection and minimize virus shedding that can help in decreasing virus load in the environment.