First anticoccidial sensitivity test applied to Eimeria lata: evidence of reduced sensitivity to nicarbazin in a Brazilian field isolate.

Eimeria lata is a recently characterized species of domestic chicken whose sensitivity to anticoccidial drugs remains largely unknown. This study aimed to determine the anticoccidial sensitivity profile of the Brazilian E. lata BR-AMC isolate, obtained from alternative production systems, through an anticoccidial sensitivity test (AST). One hundred ninety-two broiler chicks were allocated into six treatment groups: unmedicated, non-challenged; unmedicated, challenged; and challenged groups medicated with nicarbazin (100 ppm), salinomycin (72 ppm), lasalocid (75 ppm), or semduramicin (22.5 ppm). Birds were orally challenged with 20,000 sporulated oocysts. Sensitivity was assessed using three complementary parameters: oocyst output reduction, the percentage of optimum anticoccidial activity (POAA), and body weight gain (BWG). All tested drugs reduced oocyst output by more than 80%, indicating sensitivity to all of them by this parameter. Nevertheless, based on POAA, E. lata was sensitive to salinomycin (96%) and lasalocid (130%), partially sensitive to semduramicin (72%), and resistant to nicarbazin (40%). BWG results demonstrated sensitivity to lasalocid, salinomycin and semduramicin, while results for nicarbazin were inconclusive. When taken together and based on the interpretation criteria adopted in this study, these divergent results indicate reduced sensitivity to nicarbazin and sensitivity to lasalocid, salinomycin, and semduramicin, underlining the importance of multi-parameter approaches when conducting ASTs. Furthermore, although based on a single isolate, our results also raise the possibility that alternative rearing systems may harbor drug-resistant Eimeria strains, an epidemiological concern that warrants further investigation.