Abstract
A reverse transcriptase polymerase chain reaction restriction fragment length polymorphism (RT-PCR/RFLP) technique was used for the identification and characterization of Pakistani field isolates of infectious bursal disease virus (IBDV). A total of 8 bursa samples were collected from two outbreaks during September and October 2003 from Tehsil Sumandri, Dist. Faisalabad with 40-50% mortality in commercially reared broiler chicken flocks experiencing signs typical of infectious bursal disease (IBD). Four samples were found to contain IBDV genome by One Step RTPCR using VP2 gene specific primers. The assay amplified a 743 bp fragment from 701-1444 nucleotides. RT-PCR product was further subjected to restriction digestion using MboI and MvaI restriction enzymes. A third enzyme SspI was used to identify the very virulent phenotype. The RFLP profile was found similar for all four isolates with MvaI enzyme but different for one isolate when digested with MboI. All three MvaI-positive viruses were further found positive for SspI digestion and yielded RFLP profile similar to vvIBDV in Europe whereas one isolate was SspI negative and had a RFLP profile similar to classic IBDV strains. The clinical history of high mortality and SspI restriction enzyme positivity revealed that vvIBDV strains exist in Pakistan.
Highlights
Infectious bursal disease is an acute, highly contagious viral disease of young chickens that causes significant losses to the poultry industry worldwide [12]
The mortality percentage observed during the study is the result of very virulent Infectious bursal disease virus (IBDV) outbreaks which already have been well reported in the literature (Lukert and Saif, 2003; Zahoor et al, 2005)
The vvIBDV can cause more than 70% mortality; we previously have shown that vvIBDV in Faisalabad caused 43.5 and 51.5% mortality respectively, in two separate outbreaks (Zahoor et al, 2005)
Summary
Infectious bursal disease is an acute, highly contagious viral disease of young chickens that causes significant losses to the poultry industry worldwide [12]. Pathotypic serotype-I IBDV strains can be grouped into classical virulent (cv), antigenic variants and very virulent (vv) [18]. Antigenic variant strains have been reported in USA, Central America [9] and in Australia [17]. The classical virulent IBDV strains cause bursal damage and lymphoid necrosis resulting into 20-30% mortality [12]. In the mid-1980s very virulent (vv) IBDV strains emerged and caused devastating outbreaks resulting in 30% mortality in broilers & 6070% mortality in layers and spread to Middle East, Asia, Africa and South America [1, 8, 19, 21, 22]. Infectious bursal disease virus (IBDV) is a member of the genus Avibirnavirus in family Birnaviridae
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