Molecular Characteristics of Infectious Bursal Disease Viruses from Asymptomatic Broiler Flocks in Europe

Abstract

Infectious bursal disease virus (IBDV) exists in several different antigenic and pathogenic forms. The immune suppression caused by this virus in young chickens is not always associated with clinical signs of disease. The antigenic variant viruses originally described in the United States typically do not cause clinical signs of disease but can cause a marked immune suppression via the destruction of B lymphocytes. Using a reverse transcription-polymerase chain reaction (RT-PCR) assay we conducted a survey of asymptomatic broiler chicken flocks in Europe for IBDV. Restriction fragment length polymorphisms in the viral protein 2 (VP2) gene of four isolates from Spain and four isolates from France indicated they may be different from the classic and very virulent (vv) IBDV strains found throughout Europe. Nucleotide sequence and phylogenetic analysis of the hypervariable region of the VP2 gene indicated that all eight viruses were more similar to U.S. variant viruses than classic viruses. In two viruses, one from France and one from Spain, threonine was observed at amino acid position 222 and serine was found at position 254. These two substitution mutations are characteristic of Delaware variant viruses. In addition, all eight viruses had mutated amino acid position 318 from glycine to aspartic acid, another substitution mutation commonly found in U.S. variant viruses. Although importation restrictions prevented us from directly testing the antigenicity of these viruses, their nucleotide and predicted amino acid sequences suggest they could be antigenically distinctive compared to classic and vvIBDV commonly found in Europe. Confirmation of the presence of antigenic variant IBDV strains in Europe requires additional immunologic studies to elucidate the exact nature of the viral epitopes. Our data support the need for these immunologic studies.

Molecular and Structural Bases for the Antigenicity of VP2 of Infectious Bursal Disease Virus

“…This seems plausible, since Domanska et al (9) described sequences of IBDV strains present during the late 1970s and early 1980s in Europe containing a serine at position 222 and causing subclinical infectious bursal disease. Interestingly, Jackwood et al (14) recently reported the presence of new IBDV isolates in Europe with VP2 sequences distinct from those of previous European IBDV isolates (classical and very virulent) and Belg-IBDV. The sequences were highly related to an IBDV variant circulating in the United States.…”

Detection of Infectious Bursal Disease Virus Isolates with Unknown Antigenic Properties by Reverse Genetics

“…This is necessary because it is possible that the analyzed viral sequences represent viral populations that are present in the bursal sample but are impeded because of a decreased ability to replicate in the host. Emergence and evolution of new antigenic variants has been documented since the mid-1980s in the United States (24,26) and, most recently, in Europe (7,14).…”

Differential modulation of cytokine, chemokine and Toll like receptor expression in chickens infected with classical and variant infectious bursal disease virus

“…The virus infects and destroys actively dividing IgM-bearing B cells in the bursa of fabricius [2,3]. IBDV exists in different antigenic and pathogenic forms [4]. Initial isolates designated as classical strains (cIBDV) of the serotype 1 viruses were considered to be a single antigenic type.…”