Comparison of three different methods for the diagnosis of bovine Paratuberculosis in infected dairy herds

Abstract

The sensitivity and specificity of the direct microscopic examination of faeces (Ziehl Neelsen stain), faecal culture (Modified Herrolds Medium) and a serological test (ELISA) used for the diagnosis of bovine Paratuberculosis was compared in 250 asymptomatic animals from 14 infected dairy herds. All faecal samples were simultaneously examined by the two bacteriological methods and the isolated cultures identified by PCR technology. The serological diagnosis was performed using a commercial kit of an ELISA test (IDEXX) with a photometric reader at 620 nm and a cut off of OD 0.25. Myccobacterium avium subsp. paratuberculosis (Map) was isolated in 71.4% (10) of herds and 16.0% (40) of animals. No positive samples were found when examined by the Ziehl Neelsen method, although a doubtful result was recorded in 35 (14.0%) faecal samples, 6 (17.0%) of which were also culture positive (kappa: 0.013). The serological test detected 8.0% (20) of positive reactors with a sensitivity of 96.7% and a specificity of 32.5% (kappa: 0.366). These results show the advantage of using simultaneously both faecal culture and serology for the diagnosis of infected but asymptomatic animals and the uselessness of the direct microscopic examination of faeces as diagnostic method of Paratuberculosis in subclinically infected animals.