Of the two known serotypes of IBDV, only '''Serotype I''' is pathogenic, causing bursal disease in '''chicks''' by '''selectively''' infecting the cells of the '''[[Bursa of Fabricius]]'''. | Of the two known serotypes of IBDV, only '''Serotype I''' is pathogenic, causing bursal disease in '''chicks''' by '''selectively''' infecting the cells of the '''[[Bursa of Fabricius]]'''. |