Sequence-based comparison of field and vaccine strains of infectious bursal disease virus in Ethiopia reveals an amino acid mismatch in the immunodominant VP2 protein

Dereje Shegu,Asaminew Tesfaye,Belayneh Getachew,Takele Abayneh,Hawa Mohammed,Alebachew Belay,Teshale Sori,Teferi Degefa,Esayas Gelaye

doi:10.1007/s00705-020-04622-6

Abstract

Sequencing of the VP2 region was carried out to identify amino acid mismatches between vaccine strains and field isolates of infectious bursal disease virus (IBDV). Viruses were isolated in chicken embryo fibroblast (DF-1) cells using pooled samples of bursa collected from nine outbreaks, which affected 30,250 chickens in five localities, with an overall mortality of 47.87%. Virus strains were identified by comparing the deduced amino acid sequence between positions 232 and 446 of the immunodominant VP2 epitope. All of the pooled samples were positive for IBDV. RT-PCR yielded a 645-bp DNA fragment of the VP2 gene. Phylogenetic analysis of this fragment revealed clustering of these isolates with very virulent IBDV strains. The amino acid sequences of these isolates were identical to those of the European very virulent strains UK 661 and DV 86, except at position 222, but differed from the vaccine strains used in Ethiopia, suggesting the possible introduction of virulent virus strains to Ethiopia from Europe. Our study demonstrates the widespread presence of very virulent strains of IBDV on poultry farms in Ethiopia and demonstrates the need to evaluate the protective level of existing vaccines against circulating field viruses.

Highlights

Chicken production plays an important role in Ethiopia, providing cash for women and children to buy clothing and school supplies, cover medical costs, and much more [8, 22]
Nine of the samples that produced CPE were selected and tested using reverse transcriptase polymerase chain reaction (RT-PCR) targeting the VP2 gene of infectious bursal disease virus (IBDV), which resulted in a 645-bp PCR product (Fig. 2), confirming the identity of the virus
The IBDV isolates from Bishoftu, Asella, and Kombolcha had amino acid sequences that were more similar to those of the British strain UK661 and the Dutch strain DV86 than to the vaccine strains commonly used to vaccinate chickens in Ethiopia, such as LC75 and D78

Summary

Introduction

Chicken production plays an important role in Ethiopia, providing cash for women and children to buy clothing and school supplies, cover medical costs, and much more [8, 22]. IBD is an acute, highly contagious viral disease of 3- to 6-week-old chickens that causes significant losses to the poultry industry. In Ethiopia, IBD was first reported in Debre Zeit in 2002 on a commercial farm where a live vaccine imported from the Netherlands was being used [32]. Since it has been prevalent in various regions [33], causing high mortality, ranging from 50% to 72%, in chickens [29, 34]. The disease is considered one of the important constraints to the poultry industry throughout the country [17]

Methods

Results

Conclusion