Eventually animals will become emaciated and die. Animals are generally infected by ingestion of the organism, which is shed through the feces, colostrum, milk or in-utero. Young animals, under 6 months of age, are most susceptible, although older animals may be infected in herds with extremely high levels of infection or if other conditions place the animal under a high level of stress. Embryos placed in recipient mothers have contracted the disease from the surrogate cow. Disease is diagnosed through use of fecal culture.
Fecal culture requires a lengthy incubation period and is costly.
Quicker and less expensive blood tests are recommended to identify suspect animals for further evaluation through fecal culture. Remember, blood tests can result in false positives. Also, infected animals will generally not test positive for several months before they develop symptoms. The Johne's vaccine is available in Indiana, but must be given by a licensed veterinarian. Approval must be given by the Indiana Board of Animal Health for use of the vaccine in individual herds.