Infectious bursal disease virus: predicting viral pathotype using machine learning models focused on early changes in total blood cell counts.

Infectious bursal disease (IBD) is an avian viral disease caused in chickens by infectious bursal disease virus (IBDV). IBDV strains (Avibirnavirus genus, Birnaviridae family) exhibit different pathotypes, for which no molecular marker is available yet. The different pathotypes, ranging from sub-clinical to inducing immunosuppression and high mortality, are currently determined through a 10-day-long animal experiment designed to compare mortality and clinical score of the uncharacterized strain with references strains. Limits of this protocol lie within standardization and the extensive use of animal experimentation. The aim of this study was to establish a predictive model of viral pathotype based on a minimum number of early parameters measured during infection, allowing faster pathotyping of IBDV strains with improved ethics. We thus measured, at 2 and 4 days post-infection (dpi), the blood concentrations of various immune and coagulation related cells, the uricemia and the infectious viral load in the bursa of Fabricius of chicken infected under standardized conditions with a panel of viruses encompassing the different pathotypes of IBDV. Machine learning algorithms allowed establishing a predictive model of the pathotype based on early changes of the blood cell formula, whose accuracy reached 84.1%. Its accuracy to predict the attenuated and strictly immunosuppressive pathotypes was above 90%. The key parameters for this model were the blood concentrations of B cells, T cells, monocytes, granulocytes, thrombocytes and erythrocytes of infected chickens at 4 dpi. This predictive model could be a second option to traditional IBDV pathotyping that is faster, and more ethical.

Highly Pathogenic Avian Influenza A(H5N1) Clade 2.3.4.4b Virus in Domestic Cat, France, 2022.

We detected highly pathogenic avian influenza A(H5N1) clade 2.3.4.4b virus in a domestic cat that lived near a duck farm infected by a closely related virus in France during December 2022. Enhanced surveillance of symptomatic domestic carnivores in contact with infected birds is recommended to prevent further spread to mammals and humans.

Controlled Experimental Infection in Pigs with a Strain of Yersinia enterocolitica Harboring Genetic Markers for Human Pathogenicity: Colonization and Stability.

Yersinia enterocolitica (Ye) is one of the major causes of foodborne zoonosis. The BT4/O:3 bioserotype is most commonly isolated in human infections. Pigs are considered the main reservoir of Ye, and hence, understanding the dynamics of infection by this pathogen at the individual and group levels is crucial. In the present study, an experimental model was validated in Large White pigs infected with a BT4/O:3 strain. This study showed that Ye contamination in pigs may occur via the introduction of the bacteria not only by mouth but also by snout, with a colonization process consisting of three periods corresponding to three contamination statuses of pigs: P1, corresponding to the 24 h following ingestion or inhalation of Ye with the appearance of bacteria in tonsils or in feces; P2, from 2 days postinoculation (dpi), corresponding to expansion of Ye and colonization of the digestive system and extraintestinal organs associated with an IgG serological response; and P3, after 21 dpi, corresponding to regression of colonization with intermittent Ye detection in tonsils and feces. Although the inoculated strain persisted up to 56 dpi in all pigs, genetic variations with the loss of the gene yadA (a gene involved in human infection) and the emergence of two new multilocus variable-number tandem-repeat analysis (MLVA) profiles were observed in 33% of the 30 isolates studied. This experimental infection model of pigs by Ye provides new insights into the colonization steps in pigs in terms of bacterial distribution over time and bacterial genetic stability.

Evaluation of three hemagglutinin-based vaccines for the experimental control of a panzootic clade 2.3.4.4b A(H5N8) high pathogenicity avian influenza virus in mule ducks.

In France during winter 2016-2017, 487 outbreaks of clade 2.3.4.4b H5N8 subtype high pathogenicity (HP) avian influenza A virus (AIV) infections were detected in poultry and captive birds. During this epizootic, HPAIV A/decoy duck/France/161105a/2016 (H5N8) was isolated and characterized in an experimental infection transmission model in conventional mule ducks. To investigate options to possibly protect such ducks against this HPAIV, three vaccines were evaluated in controlled conditions. The first experimental vaccine was derived from the hemagglutinin gene of another clade 2.3.4.4b A(H5N8) HPAIV. It was injected at three weeks of age, either alone (Vac1) or after a primer injection at day-old (Vac1 + boost). The second vaccine (Vac2) was a commercial bivalent adjuvanted vaccine containing an expressed hemagglutinin modified from a clade 2.3.2 A(H5N1) HPAIV. Vac2 was administered as a single injection at two weeks of age. The third experimental vaccine (Vac3) also incorporated a homologous 2.3.4.4b H5 HA gene and was administered as a single injection at three weeks of age. Ducks were challenged with HPAIV A/decoy duck/France/161105a/2016 (H5N8) at six weeks of age. Post-challenge virus excretion was monitored in vaccinated and control birds every 2-3 days for two weeks using real-time reverse-transcription polymerase chain reaction and serological analyses (haemagglutination inhibition test against H5N8, H5 ELISA and AIV ELISA) were performed. Vac1 abolished oropharyngeal and cloacal shedding to almost undetectable levels, whereas Vac3 abolished cloacal shedding only (while partially reducing respiratory shedding) and Vac2 only partly reduced the respiratory and intestinal excretion of the challenge virus. These results provided relevant insights in the immunogenicity of recombinant H5 vaccines in mule ducks, a rarely investigated hybrid between Pekin and Muscovy duck species that has played a critical role in the recent H5 HPAI epizootics in France.

High antigenic diversity of serotype 1 infectious bursal disease virus revealed by antigenic cartography.

The antigenic characterization of IBDV, a virus that causes an immunosuppressive disease in young chickens, has been historically addressed using cross virus neutralization (VN) assay and antigen-capture enzyme-linked immunosorbent (AC-ELISA). However, VN assay has been usually carried out either in specific antibody negative embryonated eggs, for non-cell culture adapted strains, which is tedious, or on chicken embryo fibroblasts (CEF), which requires virus adaptation to cell culture. AC-ELISA has provided crucial information about IBDV antigenicity, but this information is limited to the epitopes included in the tested panel with a lack of information of overall antigenic view. The present work aimed at overcoming those technical limitations and providing an extensive antigenic landscape based on original cross VN assays employing primary chicken B cells, where no previous IBDV adaptation is required. Sixteen serotype 1 IBDV viruses, comprising both reference strains and documented antigenic variants were tested against eleven chicken post-infectious sera. The VN data were analysed by antigenic cartography, a method which enables reliable high-resolution quantitative and visual interpretation of large binding assay datasets. The resulting antigenic cartography revealed i) the existence of several antigenic clusters of IBDV, ii) high antigenic relatedness between some genetically unrelated viruses, iii) a highly variable contribution to global antigenicity of previously identified individual epitopes and iv) broad reactivity of chicken sera raised against antigenic variants. This study provides an overall view of IBDV antigenic diversity. Implementing this approach will be instrumental to follow the evolution of IBDV antigenicity and control the disease.

Avian metapneumovirus: A five-plex digital droplet RT-PCR method for identification of subgroups A, B, C, and D.

End-point and real-time avian metapneumovirus (AMPV) RT-PCRs have been developed to detect one or two of the four recognized subgroups (A,B,C, and D) simultaneously or for broad range AMPV detection. Current subgroup specific tests target variable areas of the genome which makes these PCRs sensitive to specificity defects as recently documented. In the current study, a single five-plex digital droplet RT-PCR targeting the conserved viral polymerase gene of AMPV, which is less prone to genetic drift, has been designed. This digital droplet RT-PCR was capable of identifying each of the four AMPV subgroups. Each subgroup was identified according to a specifically assigned fluorescent amplitude. Specificity, which was tested including 31 AMPV strains, non-AMPV avian viruses and closely related human respiratory viruses, was 100%. The specific limit of detection for extracted viral RNA was estimated between 1 and 3 copies/µl. This tool simplifies the number of tests required for AMPV genotype diagnostics and should be theoretically less effected by viral genome evolution due to its target region. Ultimately, application of this test will contribute to an improved understanding of the global geographic distribution and subgroup host range of field strains.

Multiple independent introductions of highly pathogenic avian influenza H5 viruses during the 2020-2021 epizootic in France.

During winter 2020-2021, France and other European countries were severely affected by highly pathogenic avian influenza H5 viruses of the Gs/GD/96 lineage, clade 2.3.4.4b. In total, 519 cases occurred, mainly in domestic waterfowl farms in Southwestern France. Analysis of viral genomic sequences indicated that 3 subtypes of HPAI H5 viruses were detected (H5N1, H5N3, H5N8), but most French viruses belonged to the H5N8 subtype genotype A, as Europe. Phylogenetic analyses of HPAI H5N8 viruses revealed that the French sequences were distributed in 9 genogroups, suggesting 9 independent introductions of H5N8 from wild birds, in addition to the 2 introductions of H5N1 and H5N3.

Concomitant NA and NS deletion on avian Influenza H3N1 virus associated with hen mortality in France in 2019.

An H3N1 avian influenza virus was detected in a laying hens farm in May 2019 which had experienced 25% mortality in Northern France. The complete sequencing of this virus showed that all segment sequences belonged to the Eurasian lineage and were phylogenetically very close to many of the Belgian H3N1 viruses detected in 2019. The French virus presented two genetic particularities with NA and NS deletions that could be related to virus adaptation from wild to domestic birds and could increase virulence, respectively. Molecular data of H3N1 viruses suggest that these two deletions occurred at two different times.

Full-Length Genome Sequence of a Novel European Antigenic Variant Strain of Infectious Bursal Disease Virus.

We report the full-length genome sequence (compared to reference sequences) of a novel European variant strain of infectious bursal disease virus (IBDV), designated 19P009381 (AxB1). This should help to further identify such viruses in Europe.

Infectious Bronchitis Coronavirus: Genome Evolution in Vaccinated and Non-Vaccinated SPF Chickens.

Infectious Bronchitis virus (IBV) continues to cause significant economic losses for the chicken industry despite the use of many live IBV vaccines around the world. Several authors have suggested that vaccine-induced partial protection may contribute to the emergence of new IBV strains. In order to study this hypothesis, three passages of a challenge IBV were made in SPF chickens sham inoculated or vaccinated at day of age using a live vaccine heterologous to the challenge virus. All birds that were challenged with vaccine heterologous virus were positive for viral RNA. NGS analysis of viral RNA in the unvaccinated group showed a rapid selection of seven genetic variants, finally modifying the consensus genome of the viral population. Among them, five were non-synonymous, modifying one position in NSP 8, one in NSP 13, and three in the Spike protein. In the vaccinated group, one genetic variant was selected over the three passages. This synonymous modification was absent from the unvaccinated group. Under these conditions, the genome population of an IBV challenge virus evolved rapidly in both heterologous vaccinated and non-vaccinated birds, while the genetic changes that were selected and the locations of these were very different between the two groups.

Blood B Cell Depletion Reflects Immunosuppression Induced by Live-Attenuated Infectious Bursal Disease Vaccines.

Immunosuppression in poultry production is a recurrent problem worldwide, and one of the major viral immunosuppressive agents is Infectious Bursal Disease Virus (IBDV). IBDV infections are mostly controlled by using live-attenuated vaccines. Live-attenuated Infectious Bursal Disease (IBD) vaccine candidates are classified as "mild," "intermediate," "intermediate-plus" or "hot" based on their residual immunosuppressive properties. The immunosuppression protocol described by the European Pharmacopoeia (Ph. Eur.) uses a lethal Newcastle Disease Virus (NDV) infectious challenge to measure the interference of a given IBDV vaccine candidate on NDV vaccine immune response. A Ph. Eur.-derived protocol was thus implemented to quantify immunosuppression induced by one mild, two intermediate, and four intermediate-plus live-attenuated IBD vaccines as well as a pathogenic viral strain. This protocol confirmed the respective immunosuppressive properties of those vaccines and virus. In the search for a more ethical alternative to Ph. Eur.-based protocols, two strategies were explored. First, ex vivo viral replication of those vaccines and the pathogenic strain in stimulated chicken primary bursal cells was assessed. Replication levels were not strictly correlated to immunosuppression observed in vivo. Second, changes in blood leukocyte counts in chicks were monitored using a Ph. Eur. - type protocol prior to lethal NDV challenge. In case of intermediate-plus vaccines, the drop in B cells counts was more severe. Counting blood B cells may thus represent a highly quantitative, faster, and ethical strategy than NDV challenge to assess the immunosuppression induced in chickens by live-attenuated IBD vaccines.

Description of the first isolates of guinea fowl corona and picornaviruses obtained from a case of guinea fowl fulminating enteritis.

Guinea fowl fulminating enteritis has been reported in France since the 1970s. In 2014, a coronavirus was identified and appeared as a possible viral pathogen involved in the disease. In the present study, intestinal content from a guinea fowl involved in a new case of the disease in 2017 was analysed by deep sequencing, revealing the presence of a guinea fowl coronavirus (GfCoV) and a picornavirus (GfPic). Serial passage assays into the intra-amniotic cavity of 13-day-old specific pathogen-free chicken eggs and 20-day-old conventional guinea fowl eggs were attempted. In chicken eggs, isolation assays failed, but in guinea fowl eggs, both viruses were successfully obtained. Furthermore, two GfCoV and two GfPic isolates were obtained from the same bird but from different sections of its intestines. This shows that using eggs of the same species, in which the virus has been detected, can be the key for successful isolation. The consensus sequence of the full-length genomes of both GfCoV isolates was highly similar, and correlated to those previously described in terms of genome organization, ORF length and phylogenetic clustering. According to full-length genome analysis and the structure of the Internal Ribosome Entry Site, both GfPic isolates belong to the Anativirus genus and specifically the species Anativirus B. The availability of the first isolates of GfCoV and GfPic will now provide a means of assessing their pathogenicity in guinea fowl in controlled experimental conditions and to assess whether they are primary viral pathogens of the disease "guinea fowl fulminating enteritis".RESEARCH HIGHLIGHTSFirst isolation of guinea fowl coronaviruses and picornaviruses.Eggs homologous to the infected species are key for isolation.Isolates available to precisely evaluate the virus roles in fulminating enteritis.First full-length genome sequences of guinea fowl picornaviruses.

Rabbit haemorrhagic disease virus Lagovirus europaeus/GI.1d strain: genome sequencing, in vivo virus replication kinetics, and viral dose effect.

BACKGROUND: Rabbit haemorrhagic disease virus Lagovirus europaeus/GI.1d variant (GI.1d/RHDV) was identified in 1990 in France, and until the emergence of the new genotype GI.2, it was the main variant circulating in the country. The early stages of RHDV infection have been described in a few studies of rabbits experimentally infected with earlier strains, but no information was given on the minimum infective dose. We report the genomic and phenotypic characterisation of a GI.1d/RHDV strain collected in 2000 in France (GI.1d/00-21). RESULTS: We performed in vivo assays in rabbits to study virus replication kinetics in several tissues at the early stage of infection, and to estimate the minimum infective dose. Four tested doses, negligible (10- 1 viral genome copies), low (104), high (107) and very high (1011) were quantified using a method combining density gradient centrifugation of the viral particles and an RT-qPCR technique developed to quantify genomic RNA (gRNA). The GI.1d/00-21 genome showed the same genomic organisation as other lagoviruses; however, a substitution in the 5' untranslated region and a change in the potential p23/2C-like helicase cleavage site were observed. We showed that the liver of one of the two rabbits inoculated via the oral route was infected at 16 h post-infection and all tissues at 39 h post-infection. GI.1d/00-21 induced classical RHD signs (depression) and lesions (haemorrhage and splenomegaly). Although infective dose estimation should be interpreted with caution, the minimum infective dose that infected an inoculated rabbit was lower or equal to 104 gRNA copies, whereas between 104 and 107 gRNA copies were required to also induce mortality. CONCLUSIONS: These results provide a better understanding of GI.1d/RHDV infection in rabbits. The genome analysis showed a newly observed mutation in the 5' untranslated region of a lagovirus, whose role remains unknown. The phenotypic analysis showed that the pathogenicity of GI.1d/00-21 and the replication kinetics in infected organs were close to those reported for the original GI.1 strains, and could not alone explain the observed selective advantage of the GI.1d strains. Determining the minimum dose of viral particles required to cause mortality in rabbits is an important input for in vivo studies.

Genome Evolution of Two Genetically Homogeneous Infectious Bursal Disease Virus Strains During Passages in vitro and ex vivo in the Presence of a Mutagenic Nucleoside Analog.

The avibirnavirus infectious bursal disease virus (IBDV) is responsible for a highly contagious and sometimes lethal disease of chickens (Gallus gallus). IBDV genetic variation is well-described for both field and live-attenuated vaccine strains, however, the dynamics and selection pressures behind this genetic evolution remain poorly documented. Here, genetically homogeneous virus stocks were generated using reverse genetics for a very virulent strain, rvv, and a vaccine-related strain, rCu-1. These viruses were serially passaged at controlled multiplicities of infection in several biological systems, including primary chickens B cells, the main cell type targeted by IBDV in vivo. Passages were also performed in the absence or presence of a strong selective pressure using the antiviral nucleoside analog 7-deaza-2'-C-methyladenosine (7DMA). Next Generation Sequencing (NGS) of viral genomes after the last passage in each biological system revealed that (i) a higher viral diversity was generated in segment A than in segment B, regardless 7DMA treatment and viral strain, (ii) diversity in segment B was increased by 7DMA treatment in both viruses, (iii) passaging of IBDV in primary chicken B cells, regardless of 7DMA treatment, did not select cell-culture adapted variants of rvv, preserving its capsid protein (VP2) properties, (iv) mutations in coding and non-coding regions of rCu-1 segment A could potentially associate to higher viral fitness, and (v) a specific selection, upon 7DMA addition, of a Thr329Ala substitution occurred in the viral polymerase VP1. The latter change, together with Ala270Thr change in VP2, proved to be associated with viral attenuation in vivo. These results identify genome sequences that are important for IBDV evolution in response to selection pressures. Such information will help tailor better strategies for controlling IBDV infection in chickens.

Serological Evidence of Backyard Pig Exposure to Highly Pathogenic Avian Influenza H5N8 Virus during 2016-2017 Epizootic in France.

In autumn/winter 2016-2017, HPAI-H5N8 viruses belonging to the A/goose/Guandong/1/1996 (Gs/Gd) lineage, clade 2.3.4.4b, were responsible for outbreaks in domestic poultry in Europe, and veterinarians were requested to reinforce surveillance of pigs bred in HPAI-H5Nx confirmed mixed herds. In this context, ten pig herds were visited in southwestern France from December 2016 to May 2017 and serological analyses for influenza A virus (IAV) infections were carried out by ELISA and hemagglutination inhibition assays. In one herd, one backyard pig was shown to have produced antibodies directed against a virus bearing a H5 from clade 2.3.4.4b, suggesting it would have been infected naturally after close contact with HPAI-H5N8 contaminated domestic ducks. Whereas pigs and other mammals, including humans, may have limited sensitivity to HPAI-H5 clade 2.3.4.4b, this information recalls the importance of implementing appropriate biosecurity measures in pig and poultry farms to avoid IAV interspecies transmission, a prerequisite for co-infections and subsequent emergence of new viral genotypes whose impact on both animal and human health cannot be predicted.

The impact of maturity on the ability of Eimeria acervulina and Eimeria meleagrimitis oocysts to sporulate.

The sporulation of oocysts of Eimeria that infect poultry is known to be under the influence of environmental conditions, including temperature, oxygen supply, and moisture. However, even when these conditions are optimal, the level of sporulation can remain low. The effect of oocyst maturity on their ability to sporulate was investigated for two species of Eimeria: E. acervulina of chickens, and E. meleagrimitis of turkeys. After oral infection of birds, oocysts were collected at their production site in the intestine at different times around the prepatent period. The percentage of sporulation was determined by observation of 100 oocysts for each sample. With E. acervulina, it was observed that sporulation depended on the time of collection of the oocysts in the intestine, and that it increased with aging oocysts (from 5% to 40% globally in 8 h). With E. meleagrimitis, sporulation remained low with oocysts collected in the duodenum (below 20%), but oocysts collected in the midgut and in the lower intestine sporulated more efficiently (around 80%) than oocysts collected in the duodenum at the same time. One explanation for these results is the assumption that oocysts may be produced before fertilization, and that microgametes have not yet fertilized the newly produced oocysts. As time goes on, more oocysts would be fertilized, locally in the duodenum for E. acervulina, and descending along the gut for E. meleagrimitis. This hypothesis needs to be investigated further, but it could lead to new approaches to control these parasites by targeting the microgametes.

TITLE: L'impact de la maturité sur la capacité à sporuler des oocystes d'Eimeria acervulina et d'Eimeria meleagrimitis. ABSTRACT: La sporulation des oocystes chez les Eimeria qui infectent la volaille est connue pour être influencée par les conditions environnementales (température, apport d'oxygène et humidité). Cependant, même lorsque ces conditions sont optimales, le niveau de sporulation peut rester faible. L'effet de la maturité des oocystes sur leur capacité à sporuler a été étudié pour deux espèces d'Eimeria : E. acervulina du poulet et E. meleagrimitis de la dinde. Après infection orale des oiseaux, les oocystes ont été collectés sur leur site de production dans l'intestin à différents moments autour de la période prépatente. Le pourcentage de sporulation a été déterminé en observant 100 oocystes pour chaque échantillon. Avec E. acervulina, il a été observé que le pourcentage de sporulation dépendait du moment de la collecte des oocystes dans l'intestin, et qu'il augmentait avec des oocystes vieillissants (globalement de 5 % à 40 % en 8 heures). Avec E. meleagrimitis, le pourcentage de sporulation restait faible avec les oocystes collectés dans le duodénum (inférieur à 20 %), mais les oocystes collectés dans l'intestin moyen et dans l'intestin inférieur ont sporulé plus efficacement (environ 80 %) que les oocystes recueillis dans le duodénum en même temps. Une explication de ces résultats repose sur l'hypothèse que les oocystes peuvent être produits avant la fécondation et que les microgamètes n'ont pas encore fécondé les oocystes nouvellement produits. Avec le temps, davantage d'oocystes seraient fécondés, localement dans le duodénum pour E. acervulina, et descendant le long de l'intestin pour E. meleagrimitis. Cette hypothèse doit être approfondie, mais elle peut conduire à de nouvelles approches pour contrôler ces parasites en ciblant les microgamètes.

Highly Pathogenic Avian Influenza A(H5N8) Virus Spread by Short- and Long-Range Transmission, France, 2016-17.

We detected 3 genotypes of highly pathogenic avian influenza A(H5N8) virus in France during winter 2016-17. Genotype A viruses caused dramatic economic losses in the domestic duck farm industry in southwestern France. Our phylogenetic analysis suggests that genotype A viruses formed 5 distinct geographic clusters in southwestern France. In some clusters, local secondary transmission might have been started by a single introduction. The intensity of the viral spread seems to correspond to the density of duck holdings in each production area. To avoid the introduction of disease into an unaffected area, it is crucial that authorities limit the movements of potentially infected birds.

A unified genotypic classification of infectious bursal disease virus based on both genome segments.

Infectious bursal disease virus (IBDV) of chickens is a birnavirus with a bi-segmented double-stranded RNA genome, the segments designated as A and B. We performed phylogenetic analysis using a 366-bp fragment of segment A (nt 785-1150) and a 508-bp fragment of segment B (nt 328-835) of IBDV. A total of 463 segment A and 434 segment B sequences from GenBank, including the sequences of eight recent Bangladeshi isolates, were used in the analysis. The analysis revealed eight genogroups of segment A under serotype 1, designated as A1 (classical), A2 (US antigenic variant), A3 (very virulent), A4 (dIBDV), A5 (atypical Mexican), A6 (atypical Italian), A7 (early Australian) and A8 (Australian variant), and a single genogroup under serotype 2, designated as A0. On the other hand, segment B could be categorized into five genogroups irrespective of serotype, these being B1 (classical-like), B2 (very virulent-like), B3 (early Australian-like), B4 (Polish & Tanzanian) and B5 (Nigerian). Segment B of serotype 2 strains clustered within genogroup B1. With the bi-segmented genome of IBDV, these differences would allow for a total of 45 possible assortments. Based on the combinations of segment A and segment B genogroups observed in 463 IBDV strains, a total of 15 genotypes could be recognized. Recent Bangladeshi IBDV strains, isolated in 2016, appeared to be segment reassortants having segment A of genogroup A3 (very virulent) and segment B of genogroup B3 (early Australian-like). An extended system of nomenclature of IBDV strains is proposed.

Type I Interferon acts as a major barrier to the establishment of infectious bursal disease virus (IBDV) persistent infections.

Infectious bursal disease virus (IBDV), the best characterized member of the Birnaviridae family, is a highly relevant avian pathogen causing both acute and persistent infections in different avian hosts. Here, we describe the establishment of clonal, long-term, productive persistent IBDV infections in DF-1 chicken embryonic fibroblasts. Although virus yields in persistently-infected cells are exceedingly lower than those detected in acutely infected cells, the replication fitness of viruses isolated from persistently-infected cells is higher than that of the parental virus. Persistently-infected DF-1 and IBDV-cured cell lines derived from them do not respond to type I interferon (IFN). High-throughput genome sequencing revealed that this defect is due to mutations affecting the IFNα/ß receptor subunit 2 (IFNAR2) gene resulting in the expression of IFNAR2 polypeptides harbouring large C-terminal deletions that abolish the signalling capacity of IFNα/ß receptor complex. Ectopic expression of a recombinant chicken IFNAR2 gene efficiently rescues IFNα responsiveness. IBDV-cured cell lines derived from persistently infected cells exhibit a drastically enhanced susceptibility to establishing new persistent IBDV infections. Additionally, experiments carried out with human HeLa cells lacking the IFNAR2 gene fully recapitulate results obtained with DF-1 cells, exhibiting a highly enhanced capacity to both survive the acute IBDV infection phase and to support the establishment of persistent IBDV infections. Results presented here show that the inactivation of the JAK-STAT signalling pathway significantly reduces the apoptotic response induced by the infection, hence facilitating the establishment and maintenance of IBDV persistent infections.IMPORTANCE Members of the Birnaviridae family, including infectious bursal disease virus (IBDV), exhibit a dual behaviour, causing acute infections that are often followed by the establishment of life-long persistent asymptomatic infections. Indeed, persistently infected specimens might act as efficient virus reservoirs, hence potentially contributing to virus dissemination. Despite the key importance of this biological trait, information about mechanisms triggering IBDV persistency is negligible. Our report evidences the capacity of IBDV, a highly relevant avian pathogen, to establishing long-term, productive, persistent infections in both avian and human cell lines. Data presented here provide novel and direct evidence about the crucial role of type I IFNs on the fate of IBDV-infected cells and their contribution to controlling the establishment of IBDV persistent infections. The use of cell lines unable to respond to type I IFNs opens a promising venue to unveiling additional factors contributing to IBDV persistency.