Comparative in vivo pathogenicity study of an ITA genotype isolate (G6) of infectious bursal disease virus

Abstract

Recently, a new genotype of infectious bursal disease virus (IBDV), named ITA, was detected in IBD‐vaccinated Italian broilers. Genome characterization revealed ITA to be a genetically different IBDV, belonging to genogroup 6 according to a recently proposed IBDV classification. The currently available clinical data do not allow any definition of the degree of pathogenicity of the ITA‐IBDV isolates. In the present study, a pathogenicity trial was conducted by the oral inoculation of specific‐pathogen‐free (SPF) chickens. Birds were housed in poultry isolators and inoculated at 35 days of age with an ITA‐IBDV isolate (35 birds) or a strain belonging to the G1a genogroup as a comparison (35 birds). Control birds (25 birds) were contextually mock‐inoculated with sterile water. Birds were observed daily for clinical signs and at 0, 7, 14, 21 and 28 days post‐inoculation (dpi) were bled for IBDV antibody detection. At 2, 4, 7, 14, 21 and 28 dpi, five birds from each of the inoculated groups, and three from the control group, were euthanized and subjected to a post‐mortem examination; the bursa:body weight and thymus:body weight ratios were calculated. Microscopic lesions of the bursa and thymus were scored on the basis of lymphoid necrosis and/or depletion or cortex atrophy, respectively. Both viruses induced a subclinical course of disease, as neither clinical signs nor mortality were recorded during the study, even in the presence of typical IBDV gross and microscopic lesions. Bursal damage, measured by the bursa:body weight ratio, was more noticeable and precocious after ITA‐IBDV inoculation. Histopathology scores of the bursa, indicative of rapid lymphoid depletion, confirmed the aggressiveness of the ITA‐IBDV strain in this organ. This study showed that, although the ITA‐IBDV strain tested causes infection with a subclinical course, it induces severe damage to lymphoid tissues. Therefore, its circulation in birds might be a threat for the poultry industry and may jeopardize the success of the production cycle.

Comparative Pathogenicity of Three Strains of Infectious Bursal Disease Virus Closely Related to Poultry Industry

“…The continuous emergence of new strains of IBDV and the co-existence of multiple epidemic strains have been widely reported [ 7 , 12 , 16 , 20 , 21 ]. For example, in Italy, both a new genotype ITA strain and a classic IBDV induced sub-clinical damages [ 16 ].…”

“…The continuous emergence of new strains of IBDV and the co-existence of multiple epidemic strains have been widely reported [ 7 , 12 , 16 , 20 , 21 ]. For example, in Italy, both a new genotype ITA strain and a classic IBDV induced sub-clinical damages [ 16 ]. Recently, the comparative pathogenicity of vvIBDV, classic IBDV, and reassortant IBDV circulating in Bangladesh was performed [ 21 ].…”

Alteration of immunological parameters in infectious bronchitis vaccinated–specific pathogen-free broilers after the use of different infectious bursal disease vaccines

“…New genetic lineages of IBDV continuously emerge worldwide (Michel and Jackwood, 2017) and possess different antigenic and pathogenic characteristics (Lupini et al, 2016;Felice et al, 2017;Fan et al, 2019). Independent of the pathogenicity of the strain involved and the severity of caused clinical signs, IBDV infection in chickens is always associated with damage to the bursa of Fabricius and immunosuppression (Sharma et al, 2000;Rautenschlein et al, 2003;Silveira et al, 2019;Lupini et al, 2020) which is more severe if the infection occurs during the first 3 wk of age in birds with low levels of maternally derived antibodies.…”

Infectious bursal disease virus in free‐living wild birds: A systematic review and meta‐analysis of its sero‐viroprevalence on a global scale

“…Regardless of the pathogenicity of the strain, IBDV infection damages the bursa of Fabricius and causes an immunosuppression which is more severe the younger the animals affected (Lupini et al, 2020;Rautenschlein et al, 2007;Sharma et al, 2000;Silveira et al, 2019).…”

“…Regardless of the pathogenicity of the strain, IBDV infection damages the bursa of Fabricius and causes an immunosuppression which is more severe the younger the animals affected (Lupini et al., 2020; Rautenschlein et al., 2007; Sharma et al., 2000; Silveira et al., 2019). IBDV‐related immunodeficiency indeed leads a flock to higher susceptibility to secondary bacterial infections and decreases the efficiency of vaccination programs routinely applied (Aricibasi et al., 2010).…”