Serological Assessment of Enzootic Status and Associated Risk Factors for Cattle Tick Fever in Herds from Paraíba State, Northeast Brazil.

Cattle tick fever (CTF) is the most important tick-borne disease complex affecting cattle production in tropical and subtropical regions. This study evaluated the enzootic status of CTF in cattle herds from two contrasting climatic regions of Paraíba State, Northeast Brazil, and identified epidemiological factors associated with herd immune status. A cross-sectional serological survey was conducted in 32 cattle herds from two contrasting climatic regions of Paraíba State. All herds were tested for Babesia bovis and Babesia bigemina, whereas 28 herds (14 per region) were evaluated for A. marginale. Herds were classified according to the proportion of seropositive animals for each pathogen as non-immune (≤12.5%), unstable (>12.5% to <75%), or stable (≥75%), and epidemiological factors associated with enzootic status were subsequently investigated using logistic regression models. Antibodies against at least one pathogen were detected in 55.4% (97/175) of the evaluated cattle, with higher overall seroprevalence in the Tropical Humid region (56/85; 65.9%) than in the Semi-arid region (41/90; 45.6%). Antibodies anti-B. bovis showed the lowest prevalence (24/175; 13.7%), whereas anti-A. marginale (60/155; 38.7%) and anti-B. bigemina (58/175; 33.1%) were more frequently detected. No herd was classified as enzootically stable for anti-B. bovis, whereas 6/32 (18.8%) and 3/28 (10.7%) herds achieved enzootic stability for anti-B. bigemina and anti-A. marginale, respectively. Herds composed predominantly of cattle older than five years were 97% less likely to develop protective seropositivity against B. bovis. Dairy production and animal purchase increased the odds of protective seropositivity against B. bigemina by approximately 74-fold and 10-fold, respectively, whereas needle reuse reduced the likelihood of protective seropositivity against A. marginale by 97%. These findings demonstrate that enzootic instability predominates in cattle herds from Paraíba State, indicating that natural pathogen circulation alone has been insufficient to establish consistent herd immunity against the cattle tick fever pathogens.