A retrospective analysis of domestic sheep and goat Mycobacterium avium subspecies paratuberculosis diagnostic results from the Washington Animal Disease Diagnostic Laboratory.

OBJECTIVE

To understand Mycobacterium avium subspecies paratuberculosis (MAP) diagnostic trends based on small ruminant submissions to the Washington Animal Disease Diagnostic Laboratory.

METHODS

Small ruminant MAP serum ELISA and fecal PCR results between May 1, 2015, and June 1, 2024, were obtained from Washington Animal Disease Diagnostic Laboratory. Prevalence estimates were established for goats and sheep relative to overall sample submissions, individual animals tested, and herds. Species-level differences in prevalence were evaluated based on ELISA manufacturer, age, sex, and breed.

RESULTS

A total of 108,092 small ruminant samples were submitted for MAP serum ELISA (n = 98,538 IDEXX Inc; 9,554 VMRD Inc) and 1,090 samples for fecal PCR. For sheep and goats combined, there was an overall 6-fold difference in positive prevalence between the 2 ELISA tests based on submissions (0.9% vs 5.8%), individuals (1.0% vs 5.8%), and herds (3.7% vs 24.2%). In comparison, combined fecal PCR results for sheep and goats indicated positive prevalences of 6.5% for submissions, 6.6% for individuals, and 11.2% for herds.

CONCLUSIONS

This study offers valuable insights into the prevalence of MAP infection in domestic sheep and goats across the United States, the preferred diagnostic tests among producers and veterinarians, and variations in ELISA test characteristics.

CLINICAL RELEVANCE: The results highlight the poor alignment between small ruminant MAP diagnostic usage and recommendations to use ELISA tests primarily as a screening tool for control programs in MAP-infected herds with high prevalence (≥ 5% test positive) and fecal PCR or culture-based testing to enhance surveillance, eradication, or confirmation of Johne clinical diagnoses.