Identification of a European interserotypic reassortant strain of infectious bursal disease virus

Infectious bursal disease virus (IBDV, family Birnaviridae) is a bi-segmented double-stranded RNA virus for which two serotypes are described. Serotype 1 replicates in the bursa of Fabricius and causes an immunosuppressive and potentially fatal disease in young chickens. Serotype 2 is apathogenic in poultry species. Up to now, only one natural event of interserotypic reassortment has been described after the introduction of very virulent IBDV (vvIBDV) in the USA in 2009, resulting in an IBDV strain with its segment A related to vvIBDV and its segment B related to US serotype 2 strain OH. Here, we present the first European isolate illustrative of interserotypic reassortment. The reassorting isolate, named 100056, exhibits a genomic segment A typical of current European vvIBDV but a segment B close to European serotype 2 viruses, supporting an origin distinct from US strains. When inoculated into SPF chickens, isolate 100056 induced mild clinical signs in the absence of mortality but caused a severe bursal atrophy, which strongly suggests an immunosuppressive potential. These results illustrate that interserotypic reassortment is another mechanism that can create IBDV strains with a modified acute pathogenicity. As a consequence, and for a more precise inference of the possible phenotype, care should be taken that the molecular identification of IBDV strains is targeted to both genome segments.

传染性法氏囊病病毒（Infectious bursal disease virus, IBDV，双RNA病毒科（Birnaviridae））是一种分节段双链RNA病毒，目前已报道存在两种血清型。血清1型可在法氏囊中复制，并在雏鸡中引发免疫抑制性乃至致死性疾病。血清2型对家禽无致病性。截至目前，仅在2009年超强传染性法氏囊病病毒（very virulent IBDV, vvIBDV）传入美国后，有1起自然血清型间重配事件的报道，该事件产生的IBDV毒株其A片段与vvIBDV同源，而B片段则与美国血清2型毒株OH同源。本研究报道了首个欧洲来源的血清型间重配分离株。该重配分离株命名为100056，其基因组A片段具备当前欧洲vvIBDV的典型特征，而B片段则与欧洲血清2型病毒高度相近，提示其起源与美国毒株存在差异。将该分离株接种于无特定病原体（Specific Pathogen Free, SPF）雏鸡后，仅引发轻微临床症状且无死亡病例，但造成严重的法氏囊萎缩，这强烈表明其具备免疫抑制潜力。本研究结果证实，血清型间重配是另一种可产生致病性发生改变的IBDV毒株的机制。因此，为更精准地推断毒株表型，在对IBDV毒株进行分子鉴定时，应同时靶向其两个基因组片段。