The correct option is
C Virus
Fowl-pox is also called avian diphtheria. It is a viral disease in which blisters appear on the body, mouth and over the comb. It is transmitted by the mosquitoes. It spreads by the lesions on the skin. It lasts for about 10-14 days. Vaccination mainly helps to prevent the disease. It can also spread by direct contact with the infected birds.
So, the correct answer is option D.