Thank you for your continued trust in the Washington Animal Disease Diagnostic Laboratory (WADDL) at Washington State University. We’re writing to inform you that, effective June 1, 2025, we will transition back to the Johne’s disease ELISA test kit previously used prior to October 2023 for all small ruminant submissions.
This decision follows a thorough internal review and is based on several key considerations:
- Client feedback: Over the past several months, we’ve received consistent input from small ruminant clients noting an increase in Johne’s ELISA-positive results, especially in goats.
- Historical data review: We analyzed WADDL’s testing data from the past 10 years and observed a marked increase in positivity rates following the adoption of the current test kit in October 2023. While the true disease status of tested animals is inherently unknown, the trend raised valid concerns.
- Internal test comparison: We conducted a side-by-side comparison of the current and previous ELISA kits using goat serum samples.
- Qualitative agreement between the tests was poor (κ = 0.146), indicating the two kits often disagreed on positive/negative results.
- Quantitative trends were consistent, but the current kit tended to produce more positive results, while the previous kit yielded more negatives.
- Interlaboratory Collaboration: Discussion and collaboration with several other AAVLD-accredited laboratories across the United States revealed the current ELISA kit was functioning similarly at other laboratories as at WADDL.
These findings suggest that the current test may have higher diagnostic sensitivity, whereas the previous test appears to offer greater diagnostic specificity. While both attributes are important, specificity is especially critical when evaluating small ruminants, where test results are often used to make decisions about individual animals rather than herd-level trends.
We understand that diagnosing Johne’s disease in live animals—especially goats and sheep—can be challenging, and no test is perfect. Your feedback, combined with careful data analysis, has been essential in guiding this decision and maintaining our commitment to diagnostic quality.
If you have any questions, concerns, or would like to provide additional feedback, please feel free to reach out directly to Dr. Korakrit Poonsuk, Immunodiagnostic Section Head, at Korakrit.poonsuk@wsu.edu. He would be happy to discuss the test change and answer any questions you may have.
At WADDL, our highest priority is to provide test results that are accurate, reliable, and actionable. We remain committed to using USDA-licensed assays whenever appropriate and will continue to update our protocols as improved tools become available.
We appreciate your continued partnership and support.