The Single Intradermal Cervical Comparative Test Interferes with Johne's Disease ELISA Diagnostics

Area of Science:

• Veterinary immunology
• Bovine infectious diseases
• Diagnostic assay development

Background:

• Enzyme-linked immunosorbent assays (ELISA) are crucial for screening herds for Mycobacterium avium subspecies paratuberculosis (MAP), the causative agent of Johne's disease (JD).
• Previous reports suggest that purified protein derivative (PPD) administration for bovine tuberculosis (bTB) testing can interfere with the sensitivity and specificity of MAP ELISA tests in seronegative cattle.
• Understanding this interference is vital for accurate JD diagnosis and herd management.

Purpose of the Study:

• To investigate the impact of the single intradermal cervical comparative test (SICCT) for bTB on both serum and milk MAP ELISA results.
• To determine the optimal timing for JD ELISA testing in relation to SICCT administration.

Main Methods:

• A herd of 139 cows was sampled for serum and milk ELISA for MAP before and after SICCT administration.
• The ID Screen Paratuberculosis Indirect Screening Test (ID Vet) was used for screening.
• Statistical analysis was performed to assess changes in ELISA prevalence and values over time post-SICCT.

Main Results:

• Within 14 days of PPD administration, a significant increase in seropositive cows for MAP was observed in both milk and serum samples (39% prevalence).
• ELISA values remained significantly elevated until day 43 post-SICCT in milk and day 71 in serum.
• The study suggests that PPD administration may induce cross-reacting antibodies, potentially leading to false positives in JD ELISA tests.

Conclusions:

• Milk ELISA for JD should be avoided within 43 days following PPD administration due to potential interference from SICCT.
• Serum ELISA for JD should be avoided for 71 days post-SICCT.
• Milk ELISA may be more suitable than serum ELISA for JD testing within two months of bTB testing if cross-reacting antibodies are a concern.