UTILITY OF LOCALLY ISOLATED FOWL POX VIRUS DURING 2019FOR POTENCY EVALUATION OF CURRENTLY USED VACCINES

This study was conducted to evaluate the efficacy of commercial Fowl Pox Virus (FPV) vaccines against re-emerged locally isolated strain late 2018, namely FWPVH/Egypt/2018. FPV was isolated from affected chickens in laying hen's farm in Qalubya governorate late 2018. Virus isolation and titration were carried out on collected nodular skin lesions, on the
chorioallantoic membrane (CAM) of specific pathogen free (SPF) embryonated chicken eggs (ECE). Characteristic pox lesions of FPV were obtained with a virus titer of 6.0 log10 EID50/ml at the 5th virus passage.Further identification achieved by polymerase chain reaction (PCR) amplifying 578 bp and 1982 bp of P4b (fpv167) and fpv140 genes of isolated FPV,
respectively. Molecular characterization of the virus was obtained by nucleotide sequencing of the amplified P4b fragment. However, FWPVH/Egypt/2018 showed 100% nucleotide sequence identity to FPV forming a single cluster at subclade A1 with other FP and it shared only 90% nucleotide identity to pigeon pox viruses (PPV) which clustered in subclade A2.
To evaluate the efficacy of commercial FPV and PPV vaccines to protect chickens against challenge with FWPVH/Egypt/2018, five groups of SPF chicks were vaccinated with five available commercial market vaccines FPV (VSVRI), FPV (Diftosec-Merial), FPV poxin, FPV (Intervet) and, PPV (VSVRI). Percentage of take count for each group were 100, 95, 95, 95, and 85, respectively.Virus neutralization test (VNT) using collected serum samples of vaccinated chicks groups against FWPVH/Egypt/2018 revealed 3, 3, 2.75, 2.75, and 2.25 neutralization index (NI),respectively, showing high antigenic relationship between vaccinal FPV and isolated FPV but lower antigenic relationship to PPV Vaccine. Protection percentages against challenge with FWPVH/Egypt/2018 were100. 95, 95, 95 and 85%, respectively,for used commercial vaccines.Protection was 0% in control non-vaccinated group. The present study reports the antigenic and genetic similarity between the tested commercial vaccines and the re-emerged locally isolated FPV strain (FWPVH/Egypt/2018) and the utility of the strain to be used as a challenge virus to evaluate commercial vaccines used against FPV