advanced studies on protection to infectious bursal disease in chickens
Molecular and sequence analysis of the complete VP2 gene (1356 pb) of four Egyptian IBDV isolates circulating in Egypt during 1998-2014 confirm the existence and circulation of very virulent strains of IBDV in the field. The four Egyptian isolates possess unique amino acids substitutions within the hyper variable region of VP2 that differ from those of other analyzed reference IBDV strains. All vvIBD viruses which isolated from 1998 until 2014 are still pathogenic and cause bursal atrophy. Pathogenicity study with 4 different vvIBDV local field isolates designated as "Lay/Giza.Egypt/98", " Lay/Sharkia.Egypt/03", "Br/Egy.Kalubia/07" and "Br/Giza.Egypt /014" indicated that the isolates are highly virulent pathotypes producing 23%, 37%, 23% and 50% mortality respectively in susceptible commercial male layer chickens at 59 day-old age. The local field isolate vvIBDV "Br./Giza. Egypt/14 " cause more severe bursal atrophy in comparable with other local field isolates and that were represented by BI and MSI. Laboratory vaccination experiment designed to evaluate the degree of protection against vvIBDV infection by vaccination with HVT-IBD vector vaccine in broiler chickens challenged with 3 different vvIBDV local field isolates at 35-days of age "Lay./Giza.Egypt/98, "Br./Egy.Kalubia/07 and "Br./Giza. Egypt/14 "in which there was no mortality in all vaccinated groups while the mortality rate was 1/20 (5%) in non-vaccinated group challenged with"Br./Giza. Egypt/14 "isolate and so HVT-IBD vector vaccine could protect 100% of vaccinated broiler chickens against mortality versus 5% in non-vaccinated challenged chickens with vvIBDV local field isolate "Br/Giza.Egypt /014". Broiler chickens vaccinated with HVT-IBD vector vaccine also protected from gross bursal lesion and bursal atrophy when challenged at 35-days of age with our three different isolates "Lay./Giza.Egypt/98, "Br./Egy.Kalubia/07" and "Br./Giza. Egypt/14 ". There was partial protection of vaccinated challenged broiler chickens represented by BI and MSI versus to non-vaccinated control chickens at 7-days post challenge, respectively. Vaccination with HVT-IBD vector vaccine protect against mortality and reduce its level than the non-vaccinated groups.