Introduction
Tick-borne fever (TF) pathogens, including Anaplasma marginale and Babesia species (B. bovis and B. bigemina), pose a persistent challenge in tropical beef systems. Enzootic stability—where most animals harbor antibodies without clinical disease—helps farmers maintain herd health even as pathogen exposure continues. A recent field comparison on a commercial Brazilian cattle farm explored whether strategic tick control with fluralaner (Exzolt® 5%) would alter enzootic stability compared with a farm-practice pour-on of fipronil + fluazuron (TickGard®). The study ran from October 2023 to May 2024 in Rio Verde, Goiás, Brazil, a tropical region with distinct rainy and dry seasons and high Rhipicephalus microplus pressure.
Experimental design
Two groups of 3/4 European × 1/4 Nelore calves (n = 100; 50 per group) were studied from infancy (about 25 days old) to weaning (approximately 241 days). The FIFLUA group received farm-standard TickGard® treatments, while the FLU group received fluralaner (Exzolt® 5%) every time re-treatment criteria were met (i.e., when >30% of the herd had ticks smaller than 4 mm). Both groups grazed separately with their mothers, feeding on pasture and maternal milk, with their own distinct tick challenges and pathogen exposures.
Measures of enzootic stability
Enzootic stability for TF pathogens was assessed using:
- Indirect ELISA (iELISA) for antibodies against A. marginale, B. bovis, and B. bigemina on days 25, 60, 135, 188, and 241.
- Quantitative PCR (qPCR) on blood samples to detect DNA from A. marginale, B. bovis, and B. bigemina, at the same intervals.
- Blood smears to monitor parasitemia/bacteremia as supportive data (lower sensitivity for enzootic status).
Enzootic stability was defined as more than 75% of animals seropositive for a given pathogen, in line with established references.
Key findings: tick burden and pathogen exposure
Tick counts showed that the FLU group (fluralaner) generally had lower tick burdens over time, notably at 60 and 241 days, though the FIFLUA group showed lower counts at 135 days. Importantly, the FLU group did not experience clinical TF outbreaks; instead, tick exposure remained controlled enough to prevent disease while maintaining pathogen contact that drives immunity.
Pathogen exposure measured by qPCR revealed different patterns between groups but did not indicate a failure of enzootic stability in the fluralaner group. Specifically:
- B. bovis: qPCR positivity rose in both groups with age; however, stability as defined by serology was reached earlier in the FLU group (133 days) than in the FIFLUA group (188 days).
- B. bigemina: iELISA indicated stability earlier in FLU (60 days) versus FIFLUA (188 days).
- A. marginale: FLU achieved stability by 188 days, while FIFLUA reached stability at 241 days.
Overall, serology showed higher mean antibody titres for the FLU group across pathogens, suggesting active exposure at a controlled level that supports enzootic stability rather than undermining it. The observed pattern aligns with the concept that strategic fluralaner use can reduce tick challenge without eliminating tick/pathogen contact necessary for maintaining herd immunity.
Practical implications for tropical beef systems
The study supports the view that strategic deployment of fluralaner can lower tick burden and bacteremia (e.g., A. marginale) while preserving or even advancing enzootic stability against TF pathogens. Notably, the FLU strategy kept calves in contact with ticks and pathogens just enough to sustain immunity, but with fewer clinical episodes and reduced risk of severe disease during the early, vulnerable weeks.
From a farm-management perspective, the FLU approach may offer several advantages over conventional pour-on programs:
– Potentially longer intervals between treatments due to high initial efficacy against R. microplus
– Reduced tick burden and fewer overt TF infections in calves
– Maintained enzootic stability, lowering the risk of disease outbreaks at weaning or early life
– Adaptability to tropical climates where R. microplus can have multiple generations per year
Conclusion
Under the conditions of this tropical Brazilian farm, strategic tick control with fluralaner did not disrupt enzootic stability for the major TF pathogens. In fact, fluralaner-treated calves showed earlier seropositive status for B. bovis and B. bigemina and comparable or higher titres for A. marginale, with lower tick burdens and fewer clinical events. These results support the use of fluralaner as part of an integrated tick-control program that manages disease risk while preserving herd-level immunity in crossbred beef calves in tropical climates.
