Association of Different Diagnostic Methods Used to Identify Coccidiosis in Broiler Chickens and Potentially Associated Bacterial Lesions.

Coccidiosis is a major avian enteropathy caused by Eimeria spp., and mixed infections can hinder diagnosis due to overlapping lesions. This study aimed to evaluate the occurrence of coccidiosis in broiler chickens through characterization of gross and histopathologic lesions, parasitologic identification, and investigation of potentially associated bacterial infections. A cross-sectional study was conducted on 28 flocks housed in positive-pressure ventilated poultry houses, with a sample of 280 broilers collected at two time points: sampling 1 (21 to 28 days of age) and sampling 2 (35 to 42 days of age). Analyses included scoring of gross and histopathologic lesions, morphometric and morphologic assessment of Eimeria oocysts, Salmonella testing in feces and litter, and aerobic bacterial culture of organs with lesions. Eimeria spp. positivity was 82.14% in sampling 1 and 100% in sampling 2. Oocysts morphologically consistent with Eimeria acervulina predominated initially, while Eimeria tenella was most frequent later. Due to morphometric overlap among species, identification was based solely on morphology and not confirmed molecularly. Mixed infections were frequent. Histopathology showed higher diagnostic sensitivity, with a 28.5% increase in positive case detection compared to gross evaluation. Grade 1 lesions were predominant at both time points, except in sampling 2, where E. tenella was responsible for a higher frequency of grade 3 lesions. No flocks tested positive for Salmonella. Opportunistic bacteria (Escherichia coli, coagulase-negative Staphylococcus) were isolated in broilers with septic extraintestinal lesions, including airsacculitis, perihepatitis, pericarditis, hepatitis, and splenitis, with no significant association with coccidiosis. The results reinforce the importance of integrating diagnostic methods to increase the accuracy of disease detection and suggest that the low incidence of bacterial infections may reflect appropriate biosecurity practices on the evaluated farms.