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Paratuberculosis (PTB) or Johne's disease is a common ruminant infectious disease caused by Mycobacterium avium subsp. paratuberculosis (MAP). In this study, two MAP antigens were compared for their diagnostic utility to detect subclinical PTB in a sheep flock in Mexicali, Mexico. Sheep (n = 31) without clinical signs but positive on a direct fecal-polymerase chain reaction were tested with two preabsorbed in-house enzyme linked immunosorbent assays (ELISAs) using: (1) an ethanol-extracted surface lipid antigen (EVELISA) and (2) a protoplasmic antigen (ELISA-PPA). Sensitivities of the EVELISA and ELISA-PPA were 84% (95% CI; 66-95%) and 29% (95% CI; 14-48%), respectively. The EVELISA test could be a fast and effective way to identify subclinical ovine PTB for severely affected flocks.

A commercially available multi-antigen lateral flow assay (LFA) for detection of antibodies to Mycobacterium bovis was evaluated by testing dairy cattle in Baja California, México. Sera and tissue samples were obtained from 268 dairy cattle at a slaughterhouse and were tested by LFA, bacteriological culture, and polymerase chain reaction (PCR). Of 107 culture positive samples, 70 (65.4%) were positive by PCR and 49 (45.8%) were positive by LFA. The PCR and LFA gave positive results with an additional 59 (36.6%) and 77 (47.8%) of the 161 culture negative samples, respectively. The false negative rate for the PCR was 34.6% and 54.2% for the LFA. Due to the high false positive rate for both PCR and LFA observed in this study, the LFA cannot be a useful test, even in combination with PCR.