Prevalence of paratuberculosis (Mycobacterium avium subspecies paratuberculosis) in specialized dairy herds in Costa Rica

A cross-sectional study was conducted in 194 specialized dairy herds in Costa Rica, to determine the prevalence of Mycobacterium avium subspecies paratuberculosis (MAP) in herds at a national level and by administrative regions. Bulk milk samples were taken twice, three months apart; the sera was analyzed using an immunoassay. Overall MAP prevalence of herds was 79.4%; a total of 70.1% of the herds showed low prevalence and 9.3% showed high prevalence. Changes were observed in 43.8% of the herds analyzed between the first and the second sampling: 16 of 47 changed from negative to positive, while 45 of 122 changed from positive to negative. Spatial analysis of the distribution of MAP seropositive and negative herds indicated no significant difference in the average central location of both groups. Significant differences were found in MAP prevalence based on differences in life zones and precipitation. A greater proportion of MAP negative farms was found in the lower montane rain forest (Z= -2.0289; P= 0.0424), and in precipitation ranges of 4000-8000 mm (Z= -2.9920; P= 0.0028), while a greater proportion of seropositive farms were found in the precipitation ranges of 1000-2000 mm (Z= 2.5137; P= 0.0121). Considering the epidemiology of MAP and the low sensitivity of the Paratuberculosis ELISA, it may be concluded that a considerable amount of potentially infected herds were not detected, resulting in an estimated high prevalence, nationwide. This study may be detecting only a part of the problem that paratuberculosis poses for the dairy industry in Costa Rica.