Infectious bursal disease.

Abstract

Abstract Infectious bursal disease virus (IBDV), a double stranded RNA virus belonging to the genus Avibirnavirus and family Birnaviridae, is the causative agent of infectious bursal disease (IBD) (Luque et al., 2009). IBDV shows selective tropism for lymphoid tissues especially bursa of Fabricius and causes an acute and highly contagious viral disease which is manifested with inflammation and subsequently atrophy of the bursa of Fabricius, immunosuppression and various degrees of nephroso-nephritis in chickens between 3 weeks and 3 months of age (Berg, 2000; Eterradossi and Saif, 2008; Mahgoub, 2012; Müller et al., 2012). First recognized in Gumboro, Delaware (USA) in 1962, the disease was initially referred to as avian nephrosis, and later became known as Gumboro disease or infectious bursitis. Economic losses are high and are manifested in two ways. First, in the case of classical IBD, because of high mortality in chickens of 3-6 weeks and prolonged immunosuppression leading to secondary infections and vaccination failures (Ingrao et al., 2013). The virus occurs worldwide, and despite intensive vaccination regimes, outbreaks of disease occur frequently, and various variants of IBDV occur, each with a different virulence. At the end of the 1980s, very virulent variants of IBDV (vvIBDV) emerged, initially in Europe, and subsequently in Asia, the Middle East and South America. vvIBDV may cause acute disease in susceptible flocks over the entire growing period of broilers, in which the virus invades non-bursal and haematopoietic organs, such as the thymus, spleen and bone marrow. In many cases, the classical vaccines failed to provide sufficient protection against vvIBD (Fan et al., 2020). Thus novel vaccine technologies are being applied to design more effective vaccine and vaccination strategies against vvIBDV. The aim is to develop new, tailor-made live or inactivated (subunit) vaccines that protect against both classical and vvIBDV strains. They should have the potency of 'hot' live vaccines, without the accompanying dangers of causing immunosuppression. In particular the interference of maternal derived antibodies must be overcome. The development of marker vaccines that provide the ability to distinguish between vaccinal and infectious antibodies, would allow monitoring of the epidemiological field situation (Alkie and Rautenschlein, 2016).