Very Virulent Infectious Bursal Disease Virus Produces More-Severe Disease and Lesions in Specific-Pathogen-Free (SPF) Leghorns Than in SPF Broiler Chickens

Abstract

Infectious bursal disease virus (IBDV) is an important pathogen of chickens causing negative economic impacts in poultry industries worldwide. IBDV has a variable range of virulence, with very virulent (vvIBDV) strains being responsible for the greatest losses from mortality and decreased performance. Previous vvIBDV studies using conventional broilers reported resistance to lethal effects and decreased performance as compared to specific-pathogen-free (SPF) layers, but the potential contribution of the conventional vs. SPF status to resistance has not been examined. In this study we compared differences in the acute pathologic effects of infection by the California rA strain of vvIBDV for SPF white leghorn egg-laying chickens and SPF white Plymouth Rock broiler chickens over a 7-day experimental period. Based on the clinical signs and mortality observed, as well as on the more-severe pathologic changes in lymphoid tissues and kidneys, white leghorns were shown to be more susceptible to the deleterious effects of vvIBDV infection than were white Plymouth Rocks. This study provides important information on the impact of chicken breed on susceptibility to vvIBDV and the absence of impact from conventional vs. SPF status on the outcome.

Evaluation of pathological changes of natural infectious bursal disease virus infection in the lymphoid organs of Black Harco pullets

“…The presence of heterophils in the thymus of dead chickens was observed on the first day of the infection. This is in agreement with the observations of Silva et al (2016). It is interesting to note that lymphoid necrosis and depletion in the thymus was first seen on days 2 and 3 of the infection, respectively.…”

“…The damage leads to significant immunosuppressive effects on subsequent vaccinations, thereby increasing the opportunities for secondary, or susceptibility to multiple infections (Müller et al, 2003;Eterradossi & Saif, 2013). The depletion of lymphocytes in all the bursa follicles is in agreement with the findings of Oluwayelu et al (2002), Aliyu et al (2016) and Silva et al (2016). However, it was observed together with reticular cell hyperplasia as early as the first day of infection in the present study.…”

“…The present study showed that the main gross lesions during the acute phase of virulent IBDV currently circulating in Nigeria in the primary and secondary lymphoid organs of pullet chicks are initial swelling and marked haemorrhages and acute inflammation characterized by hyperaemia followed by severe atrophy of the primary lymphoid organs. These early lesions in the bursae have been described by Okoye & Uzoukwu (1982); Oluwayelu et al (2002) and Aliyu et al (2016) during natural infections while Silva et al (2016) reported same in experimental infections. However, the capacity of the field virus to induce marked gross lesions in the thymus, spleen and caecal tonsils observed in the present study was not reported in those studies.…”

“…Nielsen et al (1998) attributed the feature to an infection with virulent IBDV. Lymphocytic depletion in the lymphoid follicles, periarteriolar lymphoid sheaths, periellipsoidal lymphoid sheaths and hyperplasia of reticular cells of sheathed capillaries were marked and widespread in the present study compared to observations of various workers (Okoye & Uzoukwu, 1982;Oluwayelu et al, 2002, Aliyu et al, 2016Silva et al, 2016). The spleen filters blood and reacts immunologically to blood-borne antigens and since a large number of B cells, T cells and other immune cells exist in the spleen (Cook et al, 2000), the immune functions of B cells and T cells will be greatly decreased due to severe necrosis.…”

“…This may be responsible for the immunosuppression commonly associated with IBD in chickens (Eterradossi & Saif, 2013). This is because the bursa plays an important role in humoral immunity since it provides the necessary microenvironment for differentiation and development of B cells that produce antibodies (LeBien & Tedder, 2008;Michael, 2008).It could also be because pullet chicks are less resistant to pathologic effects of vvIBDV infections than broilers (heavy breeds) of chickens (Silva et al, 2016), although they reported severe histologic changes in the bursas of 3-week-old chickens than those in broiler chickens during experimental infections study with vvIBDV. The heterophilic infiltrations present in the spleen on day 1 of the infection indicated the acute and virulent nature of the IBDV circulating in Nigeria.…”