Seasonal transhumance sustains food security and pastoral livelihoods across Central and West Africa, but the continuous movement of millions of cattle across borders also functions as a potent, unmonitored channel for the dissemination of antimicrobial resistance (AMR). Herds traversing long-distance corridors (Chad-Cameroon-Central African Republic pastoral axis) face physical exhaustion, nutritional stress, and endemic vector pressure. Along remote pastoral corridors, the absence of clinical veterinary services drives widespread reliance on unregulated antimicrobials (predominantly oxytetracycline, beta-lactams, and sulfonamides). Sub-therapeutic dosing is common, fueled by informal administration practices, inaccurate weight estimation, and the proliferation of degraded active pharmaceutical ingredients across open-air markets.
Chronic sub-inhibitory antimicrobial exposure exerts severe selective pressure on commensal enteric bacteria like Escherichia coli and Enterococcus species. This exposure selectively enriches resistant phenotypes within the animal gut, transforming healthy carrier herds into mobile reservoirs of drug-resistant microorganisms before they ever reach terminal livestock markets or urban abattoirs.
The critical public health threat along these migration trails lies in horizontal gene transfer (HGT) and environmental amplification. Cattle shed high bacterial loads at strategic aggregation points (shared boreholes, ponds (mares)). In these dense, multi-herd convergence zones, mobile genetic elements (MGEs) such as conjugative Inc-family plasmids and Class 1 integrons facilitate the horizontal exchange of critical resistance determinants, including extended-spectrum beta-lactamase genes (bla_CTX-M) and plasmid-mediated quinolone resistance alleles (qnr). These aquatic and soil environments turn into dynamic bioreactors where resistance determinants transfer seamlessly between transient cattle, local domestic herds, and wildlife.
Addressing this silent dissemination requires a fundamental pivot from volumetric drug accounting to standardized, biomass-corrected surveillance metrics. Measuring drug consumption through indicators like the Defined Daily Dose Animal (DDDvet) and animal Population Correction Units (PCU) allows veterinary authorities to evaluate true pharmacological pressure normalized against herd biomass, separating real increases in selective exposure from routine demographic shifts in animal populations.
To intercept these molecular biosecurity threats, regional frameworks must move beyond administrative taxation at border crossings. The Support Project for the Regulation of Cross-Border Transhumance in Central Africa (PARTTAC), backed by the FAO across Cameroon, Chad, and CAR, provides an operational governance blueprint. By establishing demarcated pastoral corridors, coordinated forward veterinary posts, and sanitary checkpoints equipped for rapid screening, cross-border frameworks can integrate active AMR surveillance directly into transhumance monitoring. Coupling this infrastructure with the suppression of illicit drug markets along transit trails is essential to safeguard both pastoral resilience and regional public health under a unified One Health approach.