National BVDV eradication programme: Assessing the utility of the spot test

Area of Science:

• Veterinary Virology
• Epidemiology
• Animal Health Management

Background:

• Bovine Viral Diarrhea Virus (BVDV) eradication programs rely on accurate diagnostic testing.
• The BVDV spot test is a key tool, but its utility in identifying infected herds needs evaluation.
• False positive results and their impact on eradication strategies require investigation.

Purpose of the Study:

• To assess the accuracy of the BVDV spot test in identifying infected herds.
• To identify reasons for false positive BVDV spot test results.
• To determine the frequency of BVDV persistently infected (PI) calf births in relation to spot test results.

Main Methods:

• Analysis of BVDV test records from 3769 farm holdings participating in a national eradication program.
• Follow-up testing on herds initially identified as BVD not negative.
• Correlation of spot test results (percentage of antibody-positive samples) with PI calf births.

Main Results:

• 7.5% of holdings were initially BVD not negative; 3.5% had inconsistent follow-up results.
• Transient maternally derived antibodies in animals <270 days old were a primary cause of false positives.
• Herds with higher percentages of antibody-positive samples had significantly increased likelihood of PI calf births (OR 27.7 for >40%, OR 25.0 for 20-40%).
• Even low positivity (1-20% antibody positive) increased PI calf birth likelihood (OR 3.9).

Conclusions:

• The BVDV spot test's utility is affected by transient antibodies, leading to false positives.
• Ignoring low positive BVDV spot test results is counterproductive to national eradication goals.
• A nuanced interpretation of spot test results, considering antibody levels, is crucial for effective BVDV control.