The intravenous administration of johnin in the diagnosis of paratuberculosis in practice

Summary The diagnostic value of the intravenous injection of 1.6 or 3.2 ml of johnin was evaluated in a total of 116 cattle. The sensitivity was 84% with clinically suspect cattle. A general reaction occurred frequently as well as elevation of body temperature (average 1.47° C). The observance of a general reaction was a good additional source of information when evaluating the test. There was no significant difference in elevation of temperature between the cattle injected with 1.6 ml and those injected with 3.2 ml. A combination of diagnostic techniques such as the complement fixation test, intravenous johnin test, microscopic examination of the faeces and a biopsy examination of the rectal mucosa were necessary, in order to confirm the diagnosis of Johne's disease. In this manner a diagnosis can he confirmed with clinically suspect cattle in 96% of the cases. The sensitivity of the intravenous johnin test was considerably lower in cases of non‐clinical Johne's disease.