Department of Pathology, Faculty of Veterinary Science, Bangladesh Agricultural University, Mymensingh, 2202, Bangladesh.
Department of Livestock Services, Ministry of Fisheries and Livestock, Krishi Khamar Sarak, Dhaka, Bangladesh.
Microb Pathog. 2022 Aug;169:105641. doi: 10.1016/j.micpath.2022.105641. Epub 2022 Jun 15.
Infectious bursal disease (IBD) is a highly immunosuppressive and often fatal viral disease of young chickens. The causal agent IBD virus (IBDV) is an avian Birnavirus having two genome segments that have evolved independently and contributed to the emergence of many genotypes with different pathogenic profile. The present study aimed at genetic and pathogenic characterization of IBDVs from Bangladesh. We performed phylogenetic analysis of 15 IBDV isolates recovered from field outbreaks in chickens during 2020-2021 and compared the pathogenicity of three selected isolates belonging to different genotypes on experimental infection in chickens. Out of 15 isolates, one was the typical vvIBDV of genotype A3B2, 13 were reassortant vvIBDV of genotype A3B3 having very virulent-like segment A and early Australian-like segment B, and the remaining one isolate was a classical virulent IBDV of A1aB1 genotype. A few amino acid substitutions were observed between the genotypes in four putative antigenic sites on VP2. In a comparative pathogenicity study, the typical vvIBDV isolate BD-25(A3B2) appeared to be the most virulent with 100% morbidity and 90% mortality, followed by the segment-reassortant vvIBDV isolate BD-28(A3B3) with 50% morbidity and 30% mortality. However, the gross and histopathological lesions in the bursa of Fabricius were similar. The classical virulent isolate BD-26(A1aB1) did not cause any clinical disease. In conclusion, three genotypes of IBDV are co-circulating in poultry of Bangladesh and the typical vvIBDV of A3B2 genotype was more virulent than the reassortant vvIBDV of A3B3 genotype. Further studies are required to assess the country-wide distribution of IBDV of different genotypes and the efficacy of the currently available vaccines in protecting chickens against different genotypes of IBDV in Bangladesh.
传染性法氏囊病（IBD）是一种高度免疫抑制且常导致幼鸡死亡的病毒性疾病。病原 IBD 病毒（IBDV）是一种具有两个基因组片段的禽双 RNA 病毒，这些片段独立进化，导致许多具有不同致病谱的基因型出现。本研究旨在对来自孟加拉国的 IBDV 进行遗传和致病特征分析。我们对 2020-2021 年在鸡场暴发的 15 株 IBDV 分离株进行了系统发育分析，并比较了属于不同基因型的 3 个选定分离株在鸡的实验感染中的致病性。在 15 个分离株中，有 1 个是典型的 A3B2 基因型 vvIBDV，13 个是具有非常强毒力样 A 片段和早期澳大利亚样 B 片段的 A3B3 基因型重组 vvIBDV，还有 1 个是 A1aB1 基因型的经典强毒 IBDV。在 VP2 的 4 个假定抗原位点上，基因型之间观察到几个氨基酸取代。在比较致病性研究中，典型的 vvIBDV 分离株 BD-25（A3B2）似乎最具毒力，发病率为 100%，死亡率为 90%，其次是 A3B3 基因型的重组 vvIBDV 分离株 BD-28，发病率为 50%，死亡率为 30%。然而，法氏囊的大体和组织病理学病变相似。经典强毒分离株 BD-26（A1aB1）未引起任何临床疾病。总之，三种基因型的 IBDV 在孟加拉国的家禽中共同循环，A3B2 基因型的典型 vvIBDV 比 A3B3 基因型的重组 vvIBDV 更具毒力。需要进一步研究评估不同基因型 IBDV 在孟加拉国的全国分布以及现有疫苗在保护鸡免受不同基因型 IBDV 感染方面的效果。
