Integrated one health assessment of Cryptosporidium spp. and Giardia duodenalis occurrence on dairy farms in a megacity: evidence from animal infection, environmental contamination, and human exposure

Abstract Background Cryptosporidium spp. and Giardia duodenalis are zoonotic parasites that pose transmission risks at the livestock–human–environment interface on dairy farms. Integrated One Health studies that concurrently examine these parasites across all three reservoirs within a single farm setting remain limited. Methods A One-Health study combining repeated cross-sectional sampling of cattle and repeated longitudinal sampling at fixed environmental sites was conducted on two dairy farms in Shanghai, China, from January to December 2025. In total, 430 bovine fecal samples, 26 human fecal samples, and 96 environmental water samples were collected. Nested polymerase chain reaction targeting the small subunit rRNA gene of Cryptosporidium and the triose phosphate isomerase gene of G. duodenalis was performed, followed by phylogenetic analysis. In addition, a Knowledge, Attitudes, and Practices (KAP) survey was administered to 132 farm workers. Conclusions This comprehensive One Health investigation in a megacity dairy system identified a low prevalence of Cryptosporidium (1.40%) and G. duodenalis (1.16%) among cattle, with infections restricted to calves younger than 12 months. Cryptosporidium bovis was the predominant species, and G. duodenalis assemblages AI and E were detected. Among the 96 environmental water samples, the overall detection rates were 10.42% for Cryptosporidium and 12.50% for G. duodenalis . All of the Cryptosporidium -positive samples were from fermentation tanks (25.0%, 10/40). For G. duodenalis , source-specific detection rates were 7.50% (3/40) in fermentation tanks and 16.07% (9/56) in drinking troughs; all of the environmental isolates were identified as assemblage BIV. Phylogenetic analysis revealed considerable sequence divergence among some isolates within known parasite species. All of the human samples tested negative. The KAP survey indicated moderate awareness (51.52%) but ongoing risky practices. Although bovine prevalence was low and no human infections were detected, Cryptosporidium and G. duodenalis genetic material was detectable in farm environments, with notable genetic diversity. These findings underscore the importance of integrated surveillance and targeted interventions under a One Health framework to mitigate potential zoonotic risks.