Evaluation of the therapeutic efficacy of the sulfamidine-diaveridine combination against Vietnamese field isolate of Eimeria spp. in broiler chickens.

Avian coccidiosis remains a critical challenge in poultry production, exacerbated by the emergence of drug-resistant Eimeria field strains. This study evaluated the therapeutic efficacy of the synergistic combination of sulfamidine and diaveridine, against mixed Eimeria spp. isolate circulating in Vietnam. Experimental broilers were distributed into three groups: Negative Control (C), Challenged-Untreated (D), and the sulfamidine-diaveridine combination treated. Efficacy was assessed via oocyst output, gross and histopathological lesion scores, and the mRNA expression profiles of duodenal tight junction proteins. Results indicated that the sulfamidine-diaveridine combination significantly suppressed oocyst shedding during the acute phase 5 days post-infection (P < 0.05). However, a marked "resurgence" in oocyst output was observed at 7 dpi, eventually exceeding levels in the untreated group, suggesting reduced sensitivity of the field isolate to the sulfonamide treatment (P < 0.05). Despite the initial reduction in parasite load, gross tissue damage remained severe. Notably, molecular analysis revealed a distinct host response mechanism: the treated group exhibited a robust 5.9-fold upregulation of Claudin-3, may contribute to compensatory mechanisms aiming to restore epithelial barrier integrity (P < 0.05). In conclusion, while the sulfamidine-diaveridine combination exerts acute coccidiostatic activity and facilitates molecular barrier repair, the delayed parasitic rebound highlights the limitations of monotherapy against virulent field strains. Consequently, this formulation should be integrated into rotational drug programs to ensure sustainable disease control.