Association of fecal shedding of mycobacteria with high ELISA-determined seroprevalence for paratuberculosis in beef herds

Objective-To evaluate the seroprevalence of paratuberculosis by use of 2 commercial ELISAs in association with prevalence of fecal shedding of mycobacteria within beef cattle herds. Design-Cross-sectional field study. Animals-Six beef herds (affected herds; 522 cattle) with and 3 geographically matched herds (181 cattle) without high seroprevalence of paratuberculosis. Procedures-Blood and fecal samples were collected from adult cattle and assessed for serum anti-Mycobacterium avium subsp paratuberculosis (MAP) antibodies with 2 commercial ELISA kits and submitted for bacterial culture for MAP and environmental bacteria (termed environmental mycobacteria) via a radiometric method, respectively. Species of mycobacterial isolates were identified, and sensitivities and specificities of the 2 ELISAs were compared. Results-Compared with comparison cattle, cattle from affected herds were 9.4 times as likely to have environmental mycobacteria isolated from feces. Among the 6 affected and 3 comparison herds, the proportions of cattle shedding environmental mycobacteria were 0.225 (range, 0.1 to 0.72) and 0.04 (range, 0 to 0.06), respectively. Although relative MAP-detection specificities (compared with bacterial culture of feces) were different between the 2 ELISAs, sensitivities were not. Nine environmental mycobacterial species were identified from participating herds. All affected herds apparently had >= 1 bovid infected with MAP although MAP was not isolated from any cattle in comparison herds. Conclusions and Clinical Relevance-In beef herds with persistently high rates of false-positive ELISA results, which may be associated with recovery of environmental mycobacteria from feces, organism detection via bacterial culture of feces or PCR assay should direct paratuberculosis control measures.