Epidemiologic Indicators Associated with Within-farm Spread of Johne's Disease in Dairy Farms in Japan

Abstract

Epidemiologic indicators associated with within-farm infection of Johne's disease in dairy farms in Japan were determined through a nationwide investigation of infected farms. We assumed that subsequent detection of the disease within one year after the first detection could represent the occurrence of within-farm spread occurring before the first detection. Of 594 infected farms, 158 farms (27%) had at least one additional detection. Logistic regression analysis using epidemiologic information obtained from infected farms at the time of the first detection revealed three epidemiologic indicators associated with subsequent detection. Farms at which the first cases included cattle with clinical signs were 3.8 (95% confidence interval: 2.2, 6.8) times more likely to have additional detections than those with cattle without clinical signs. Similarly, farms where two or more cattle were detected at the time of first detection and where cattle were held in a loose housing system were 2.8 (95% CI: 1.8, 4.5) and 2.0 (95% CI: 1.1, 3.6) times more likely to have additional detections than those where only one animal was detected and a tied-up housing system was used, respectively. These epidemiologic indicators are likely important determinants in the selection of farms requiring more intensive on-farm control measures.