Presence of focal and multifocal paratuberculosis lesions in mesenteric lymph nodes and the ileocaecal valve of cattle positive to the tuberculin skin test.

The tuberculin skin test is commonly used in tuberculosis (TB) eradication programmes in cattle (Monaghan et al., 1994). The detection of false-positive reactors is important particularly in areas where there is a relatively low incidence of the disease, and can be attributed, at least in part, to immunological cross-reactivity with other mycobacteria infections. Of particular concern is Mycobacterium avium subspecies paratuberculosis (Map) infection, which is characterized by a chronic granulomatous enteritis in ruminants. The prevalence ofMap seems to be increasing in Spain where it now accounts for approximately 30.4% of positive reactors in cattle (Juste et al., 2000). Paratuberculosis immunization is also know to interfere with the diagnosis of bovine TB when single skin test is performed (Kohler et al., 2001). In order to differentiate between both mycobacterial diseases, a comparative skin test has to be carried out and the response to avian purified protein derivative (PPD) is greater than to bovine PPD in paratuberculosis infected cattle (Chiodini et al., 1984). The aim of the present study was to describe the lesions associated with paratuberculosis in adult cattle positive to the single tuberculin skin test, and to compare these with cattle negative to the tuberculin test. During the 11-month period of study, from February to December 1999, a total of 134 cattle, 4–9 years of age, was examined. Ninety-one (group 1) were positive tuberculin reactors to the single skin test, selected from 49 herds. Tuberculin skin test was performed by the in-