Paratuberculosis (Johne’s disease) is a chronic intestinal disease of ruminants and the disease is caused by Mycobacterium avium subspecies Para tuberculosis (MAP). The disease has a prolonged pre-patent period and the clinical symptoms of the disease are apparent only during the later stages of the disease. However, the infected animal can shed the organism much before the clinical disease with the risk of spreading the disease to other susceptible animals. The disease manifestation is in four stages with each of these stages requiring a different diagnostic method. During the early stages of the disease Cell mediated immune response (CMI) is higher, and shedding of the organism and serum antibody response is absent or minimized. Delayed type hypersensitivity (DTH) response upon injection of Johnin purified protein derivative (Johnin PPD) in the skin of the animal and interferon gamma release assay (IGRA) is the common CMI based tests for the diagnosis of Para tuberculosis.