Epidemiological and molecular characteristics of Infectious bursal disease virus naturally infected in the broiler flocks in the Mekong Delta of Vietnam during 2015 and 2018

Infectious bursal disease is a highly contagious and economically devastating disease in the poultry industry worldwide caused by Infectious bursal disease virus (IBDV). However, the data on epidemiological and molecular characteristics of the IBDV outbreak in broiler flocks in the Mekong Delta of Vietnam is unclear. Herein, the epidemiological data of IBDV–positive flocks over a period of 2015–2018 were recorded and the hypervariable region of the VP2 gene of IBDV was amplified to analyze the local phylogeny. The current investigation showed that the overall morbidity and mortality rates of IBDV–positive flocks were 45% and 4.81%, respectively. The IBDV–positive birds occurred clinical signs and macroscopic findings involved with the very virulent (vv) IBDV outbreak. Epidemiological results revealed that IBDV was frequently infected in broiler flocks at 12–42 days, and birds belonging to Tau Vang and Binh Dinh breeds were more sensitive to IBDV. Also, the morbidity rate of IBDV was dramatically decreased in the open farming system. Flocks with complete vaccination significantly dropped morbidity in comparison with other groups. Regarding phylogenetic analysis, all identified IBDV sequences clustered in the same branch of vv phenotype and closely homology with prior strains circulated in Vietnam and other countries. These findings first indicated the epidemiological characteristics of the IBDV–positive broiler flocks in the Mekong Delta and highlighted the IBDV strain circulating in this region.