Impact of Genogroup 4 infectious bursal disease virus on vaccinated broiler flocks in Paraná, Brazil

Infectious Bursal Disease is caused by a virus of the Birnaviridae family, belonging to the genus Avibirnavirus, which continues to represent a challenge for poultry production worldwide. In South America, genogroup 4 viral strains (dIBDV) have previously been detected in commercial broiler flocks. The emergence of variants needs to be constantly monitored to assess the risk of outbreaks even in vaccinated animals. The aim of this study was to identify the regional prevalence of dIBDV and evaluate its impacts on immune system organs and the performance of infected flocks in Parana state, Brazil. Thirty broiler flocks were evaluated, with an average of 24,949 birds per flock, aged between 18 and 23 d. Five Bursa of Fabricius samples were collected per flock for IBDV detection and genotyping. Positive samples for dIBDV in RFLP were submitted to sequencing of a fragment of the hypervariable region of the VP2 gene. Five samples of bursa of Fabricius, thymus, spleen, cecal tonsils and bone marrow were also collected per flock for histopathological analysis. Of the 30 flocks evaluated, in 10 (33%) IBDV from genogroup 4 (dIBDV) was detected. Flocks infected by dIBDV had significantly higher Bursa of Fabricius lesions than flocks negative for dIBDV. Flocks positive for dIBDV had their performance negatively impacted, through worsening feed conversion and an increase in mortality compared to negative flocks for dIBDV. In conclusion, genogroup 4 IBDV is capable of causing productive and health losses in broilers in Paraná, Brazil. The results of this study can help to better understand the dynamics of dIBDV infection in Brazil and to direct actions in the control of the disease.