Paratuberculosis in Iceland: epidemiology and control measures, past and present

Abstract

Paratuberculosis as well as the slow virus infections maedi/visna and jaagsiekte came to Iceland in 1933 when 20 sheep of the Karakul breed were imported from Halle, Germany. At least five of these sheep were subclinical carriers of paratuberculosis. Within 16 years paratuberculosis together with the other Karakul diseases (maedi/visna and jaagsiekte) almost ruined sheep farming, the main agricultural industry in Iceland. The first clinical case of paratuberculosis in sheep was confirmed in 1938, and in cattle in 1944. The first cattle cases of paratuberculosis appeared on farms where the disease had been prevalent in sheep for years. The virulence in cattle appeared to be considerably lower than in sheep. Extensive measures were used to control the spread of paratuberculosis in sheep. Hundreds of kilometres of fences were put up and used together with natural geographic borders to restrict the movement of sheep from infected areas. Serological and other immunological tests were also used to detect and dispose of infected individuals. These measures proved inadequate and the disease could not be eradicated. Culling and restocking of uninfected sheep in endemic areas eradicated maedi/visna and jaagsiekte but not paratuberculosis. Experiments showed that vaccination against paratuberculosis could reduce mortality in sheep by 94%. Vaccination of sheep in endemic areas has been compulsory in Iceland since 1966 and as a result losses have been reduced considerably. Today, serology is used to detect and control infection in cattle herds. Furthermore, serology is used to control vaccination of sheep and screen for infection in non-endemic areas. The complement fixation (CF) test for paratuberculosis has been used until now, but recently we have started comparing the CF test with the CSL absorbed ELISA test.