Johne’s disease in beef cattle: Correlation of serum ELISA and fecal PCR results from clinical cases and herd surveillance

Johne’s disease is caused by Mycobacterium avium ssp. paratu­berculosis (MAP) and can be a costly and frustrating disease in beef herds. Clinical Johne’s disease in cattle arises years after inoculation as diarrhea and progressive weight loss. Prior to reaching clinical status, subclinically infected cattle can shed bacteria into their environment, leading to continued spread of the disease within herds. The duration of subclinical infection is highly variable, and the humoral immune response and the amount of fecal shedding of MAP can vary greatly between in­dividuals and throughout the year. Currently available diagnos­tic tests (serum ELISA, fecal PCR, fecal culture) each have sig­nificant limitations. Assays may differ in their utility depending on whether they are used to confirm clinical cases of Johne’s disease or to screen healthy cattle for potential infection.