The correct option is B Virus
Gumboro disease also known as infectious bursal disease is a highly contagious disease of young chickens in which the tissues of the immune system, and especially the bursa of Fabricius, are targeted resulting in immunosuppression and susceptibility to other infections. It is caused by a virus called as infectious bursal disease virus (IBDV), which belongs to the avibirnavirus family. Clinical signs of affected birds can include depression and ruffling of feathers, poor or lack of appetite, huddling, unsteady gate, reluctance to rise, and diarrhea. The mode of transmission is primarily through the fecal-oral route. Hence, option B is correct.