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| Antigenic Characterization and Pathogenicity Study of Recent
Field Isolates of Infectious Bursal Disease Viruses |
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H.A.Sultan ,
Hussein H.A. and F.F.El-Khayat |
Abstract:
Epidemiological investigation of severe outbreaks of infectious bursal disease (IBD) occurred among vaccinated chicken flocks during the period 2002-2003 revealed that all IBDV outbreaks occurred at 18-33 days of age, 70% (21/30) of these outbreaks were characterized by typical clinical signs and gross lesions. The mortality rates in these flocks ranging between 9.4-12.8 % (average 11. 1 %); 16.4-30 % (average 23.2 %) and 12-23.5 % (average 17.75 %) in commercial broilers, commercial layer replacement pullets and native baladi varieties, respectively. On the other hand, 30% (9/30) of these outbreaks occurred at 18-21 days of age and the mortality rates ranging between 1.4-4.9% (average 3.15%) in commercial broilers and native baladi varieties, respectively. IBDV was detected in 100% of the tested bursal homogenates from acutely affected birds using agar get precipitation test (AGPT) and antigen capture ELISA (AC-ELISA). Antigenic typing of IBDV from selected outbreaks were carried out by monoclonal antibodiesbased antigen capture-enzyme linked immuno-sorbent assay (AC-ELISA) and the pathogenicity of some representative infectious bursal disease virus (IBDV) field isolates were studied. Of the selected 22 IBDV-positive bursal samples, 59.1% (13/22) were typed as classic IBDVs and 40.9% were of variant IBDVs. The majority of IBDV variant antigens detected (89% of IBDV variants) were classified as IBDV related to Del/E variant strain and one sample (11% of IBDV variants) was IBDV related to RS593 variant strain. The pathogenicity study of representative IBDV field isolates at 49-days-old egg-type chickens revealed that the highest mortality was 53.31/0 and 36.6% in birds infected with two local field isolates which typed as classic IBDVs. While in birds infected with two variants EBDVs related to Del/E and one variant IBDV related to RS593, the mortality was 10%, 13.3% and 10%, respectively. Moreover, the pathogenicity study with IBDV local field isolates indicated that IBDV related to variants Del/E or RS593 caused severe bursal atrophy (BF), as judged by bursal index (BI), in comparison to the classic vvIBDV in susceptible infected chickens. The high incidence of variant IBDV antigens detected in tested samples indicates the existence of circulating variant IBDVs despite of vaccination of flocks with classical IBDV vaccines. Regardless of the antigenic differences detected by AC-ELISA and pathogenicity test in the representative isolates, they share antigenic sites with other serotype-1 IBDV strains, as they cross-reacted in AC-ELISA and AGPT. Although, the epidemiological investigation and antigenic typing by AC-ELISA test as well as pathogenicity study suggested that those IBD field isolates are in the majority of highly virulent pathotype producing acute disease with severe clinical picture, the current study presents evidence of two variant isolates existing in commercial broiler and native baladi farms with history of problems associated with IBDV.
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How to cite this article:
H.A.Sultan , Hussein H.A. and F.F.El-Khayat , 2005. Antigenic Characterization and Pathogenicity Study of Recent
Field Isolates of Infectious Bursal Disease Viruses. International Journal of Virology, 1: 44-44.
DOI: 10.3923/ijv.2005.44.44
URL: https://scialert.net/abstract/?doi=ijv.2005.44.44
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