Evidences of circulation of new strains of Infectious Bursal Disease virus in Italian broiler farms

Significant economic losses can affect the poultry industry due to the consequences of immunosuppression induced by viral infections. This study reports the results of a preliminary survey, conducted in 2011 on six farms located in Northern Italy, aimed to investigate the effects of infectious bursal disease virus (IBDV) infection on the productive performances of broiler chickens. Four farms were located in densely populated poultry areas (DPPA) and had a history of poor performance and recurrent colisepticaemia, whereas two were located in low density poultry areas and had a history of high performance and sporadic cases of colisepticaemia. All flocks were vaccinated for IBD. Samples of the Bursa of Fabricius were collected for virus detection by RT-PCR and for histopathology from 8 birds per flock, at the 21st and between the 28th and the 35th day of life. RT-PCR products were digested with the restriction enzyme SspI to identify very virulent strains, and a fragment of the hypervariable region of the VP2 gene was sequenced. IBDV was never detected in high-performance farms, whereas it was detected in three out of four farms characterized by poor performance. In two of them, only samples collected at 21 days of age were positive, in the third one, samples collected between 28 and 35 days of age were also positive. None of the strains were very virulent IBDV. Sequencing of the hypervariable region of the VP2 gene of three IBDV strains revealed a 99% nucleotide (100% amino acid) identity between them. The detected strains differed from those described so far in Italy and showed a maximum of 92% nucleotide similarity with IBDV strains sequences published in Genebank. Histopathological lesions were observed only in bursa samples positive for IBDV. The actual spread of these IBDV strains, as well as their pathogenicity and the degree of protection offered by common vaccination schedules will be further investigated.