Prevalence and geographic distribution of Besnoitia besnoiti infection in cattle herds in Portugal.

Bovine besnoitiosis, caused by the apicomplexan parasite Besnoitia besnoiti is considered an emergent disease in Europe. This study aimed to determine the prevalence and geographic distribution of B. besnoiti in cattle herds in continental Portugal and to identify potential spatial clustering of infection. A stratified two-stage cross-sectional serological survey was carried out between March 2012 and May 2013 with the five administrative NUTS II regions, Norte, Centro, Lisboa, Alentejo, and Algarve, as the stratification level. Sera from 391 herds in 220 parishes and 83 municipalities were analyzed by a serial testing strategy, with the modified agglutination test (B-MAT) as the first screening assay and the immunofluorescent antibody test (IFAT) as the confirmatory test. Within-herd prevalence of positive herds varied between 0.7 and 72.4% and was ≥10.3% in half of the infected herds. Using a Bayesian approach, the true prevalence of B. besnoiti in cattle herds was determined to be 5.1% (confidence interval (CI), 3.1-7.8%) and the mean within-herd prevalence of positive herds was 33.0% (CI, 20.3-46.0%). The sensitivity and specificity of the B-MAT were estimated to be 96.9% (CI, 93.7-98.8 %) and 99.7% (CI, 99.6-99.8%), whereas those of the IFAT were 89.6% (CI, 86.0-92.5%) and 99.7% (CI, 98.5-99.9%), respectively. Spatial scan statistics analysis identified one spatial cluster covering the majority of the Alentejo region. Seropositive herds were detected for the first time outside Alentejo, in the region Centro and in the northeast of Portugal. Further epidemiological research is needed to identify eco-biological factors, which could explain the geographic clustering of B. besnoiti in Portugal.