TDA Labs - Large Animal Diagnostics
Johne's ELISA Tests
Johne’s Disease is a chronic, debilitating disease in cattle characterized by widespread enteritis resulting in diarrhea and weight loss. The disease is the result of infection with the bacteria Mycobacterium avium subsp. paratuberculosis. Bacteria are shed in high numbers in the feces of infected cattle and also through the milk and colostrum. Once infected, cattle are considered to be shedders for life. Shedding of bacteria by cattle increases during periods of stress such as during calving or any type of illness. Since the infection is spread by fecal ingestion of the bacteria and newborn and young calves are the most susceptible, control programs are geared toward decreasing the amount of exposure of susceptible calves to M.paratuberculosis. Identification of cows that are possible carriers and segregating them at calving is one strategy to attempt to decrease spread of Johne’s within a herd.
Fecal culture for Johne’s is considered the “gold standard” for diagnosis, but the turn around time for results is between 12-16 weeks and the culture can be quite costly. On the other hand, ELISA testing is a fast, cost-effective means of detecting the presence of Johne’s antibodies in blood. It is best used as a screening tool for groups (herds) of animals and not for making decisions on individual animals within a given herd.
Johne’s Test Specifics
The test we use is the ELISA test developed by Institut Pourquier and currently marketed by IDEXX. Results are reported as negative, inconclusive, or positive. We calculate a score based on the optical density of the test. The higher the score, the more strongly positive the result is. The assay takes 2 hours to complete once it has been started.
Johne’s Sample Handling
Blood samples should be collected in red top clot tubes. Samples can be stored for 1-3 days in the refrigerator. If samples are to be stored for 3+ days prior to testing, then serum should be separated from the clot. Ship samples on ice for receiving in 1-2 days.
ELISA testing, like any other diagnostic test, is only part of a comprehensive Johne’s control program. Each farm has different goals and needs for Johne’s control and should have a custom designed program for their specific enterprise. We would be glad to discuss any Johne’s control issues or questions you may have.
To learn more about delivering samples to the lab, visit the Samples page.
Questions may also be submitted through our online contact form.