Poultry 2022, 1, 229–243. https://doi.org/10.3390/poultry1040020 www.mdpi.com/journal/ Review A Walk through Gumboro Disease Maria Pia Franciosini 1, * and Irit Davidson 2 1 Department of Veterinary Medicine, University of Perugia Study, 06135 Perugia, Italy 2 Kimron Veterinary Institute, Bet Dagan P.O. Box 12, Israel * Correspondence: maria.franciosini@unipg.it Abstract: Infectious bursal disease (IBD), caused by an Avibirnavirus, belonging to the family Bir- naviridae, is an immunosuppressive disease that affects 3–6-week-old chickens, resulting in clinical or subclinical infection. Although clinical disease occurs in chickens, turkeys, ducks, guinea fowl, and ostriches can be also infected. IBD virus (IBDV) causes lymphoid depletion of the bursa, which is responsible for the severe depression of the humoral antibody response, primarily if this occurs within the first 2 weeks of life. IBD remains an issue in chicken meat production due to economic losses caused by the spread of variants or subtypes, resistant to the most common vaccines, respon- sible for a subclinical disease characterized by reduced growth performance and increased suscep- tibility to secondary infections. Very virulent strains of classical serotype 1 are also common in sev- eral countries and can cause severe disease with up to 90% mortality. This review mainly focuses on the immunosuppressive effect of the IBDV and potential vaccination strategies, capable of over- coming challenges associated with the optimal time for vaccination of offspring, which is dependent on maternal immunity and IBDV variant occurrence. Keywords: IBDV; variants; immunosuppression; subclinical disease; vaccination 1. Introduction Infectious bursal disease (IBD), also known as Gumboro disease, is an immunosup- pressive disease that occurs in young chickens between 3 and 6 weeks, resulting in clinical or subclinical infection, both of which are responsible for immunosuppression [1,2]. Gan- grenous dermatitis [3], coccidiosis [4], and vaccination failures are frequently associated with IBDV-induced immunosuppression [2]. In 1962, the first case of IBD was reported in Gumboro, Delaware [5]. It spread across the United States and invaded Europe in the 1970s [6]. Control of IBDV infections has been complicated by the recognition of “variant” strains of serotype 1, originating in Del- marva, USA, which caused rapid bursal atrophy without mortality and were capable of evading maternal immunity directed primarily at “classical” strains [7]. These variants or subtypes exhibited different biological properties, compared to classical strains, and could be a consequence of immune pressure due to the extensive application of vaccine plans [8]. Successively very virulent (vv) IBDV strains, responsible for 90% mortality rates, spread to the Netherlands and the United Kingdom in 1988 [9] and then to the rest of world, except Australia, New Zealand, Canada, and the United States until 2008 [10]. Sig- nificant differences between vvIBDV strains in Europe and Asia suggest independent IBDV evolution [11]. Jackwood et al. [12] concluded that approximately up to 60% of IBDV isolates worldwide belong to the vvIBDV genotype of the virus. Since then, several stud- ies have addressed the evolution of IBDV around the world, focusing on the emergence of variants [13], recombinant [14,15], and reassortant strains of the virus [16,17]. An Italian IBDV strain (ITA strain), responsible for the subclinical disease associated with a severe immunosuppression status, has been recently detected [18,19]. Whole ge- nome characterization has evidenced that ITA is genetically different from classical IBDV Citation: Franciosini, M.P.; Davidson, I. A Walk through Gumboro Disease. Poultry 2022, 1, 229–243. https://doi.org/10.3390/ poultry1040020 Academic Editor: Subir Sarker Received: 10 July 2022 Accepted: 3 October 2022 Published: 7 October 2022 Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional claims in published maps and institu- tional affiliations. Copyright: © 2022 by the authors. Li- censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con- ditions of the Creative Commons At- tribution (CC BY) license (https://cre- ativecommons.org/licenses/by/4.0/).