Estimation of the risk of cohabitation with Johne's disease-infected cattle in Japanese dairy cows.

Johne's disease is a chronic granulomatous enteritis of cattle caused by Mycobacterium avium subsp. paratuberculosis. It is one of the most important diseases in the cattle farming industry in Japan, as no effective treatment or vaccine is available. Because oral ingestion of Mycobacterium avium subsp. paratuberculosis from the feces of infected cattle is the primary route of transmission, cohabitation with infected cattle is an obvious risk factor for Johne's disease infection. This study aimed to quantify the risk of Johne's disease infection in dairy cattle due to cohabitation with infected cattle using data from the national Johne's disease surveillance and a complete set of movement histories of the relevant cattle. We also estimated the effect of cattle age on the risk of cohabitation. The relative risk of cohabitation with Johne's disease-infected cattle was 82, indicating that cohabitation with infected cattle was a significant risk factor for Johne's disease infection. When the risk of cattle cohabiting with Johne's disease-infected cattle at less than one year of age was estimated, the relative risk increased to 138, suggesting that the isolation of susceptible young cattle from potentially infected cattle is an effective preventive measure. When the relative risk was calculated for cattle cohabiting with Johne's disease-infected cattle younger than the cut-off age (two to seven years of age), the relative risk increased at a higher cut-off age, suggesting that restricting cohabitation with older cattle is more effective in mitigating Johne's disease infection.