Occurrence of Gastrointestinal Parasites in Fecal Samples from Free-Grazing Ducks in Northeastern Thailand

Intestinal parasitic infections remain a persistent concern in tropical agricultural systems, where close interactions among animals, humans, and the environment facilitate parasite transmission. Free-grazing ducks, commonly raised in rice-field ecosystems in Thailand, may be exposed to a wide range of intestinal parasites. This cross-sectional study examined 312 fecal samples collected from five selected free-grazing duck flocks in northeastern Thailand from October to November 2025. All fecal samples were examined using the modified formalin–ethyl acetate concentration technique. Parasites were identified based on egg and larval morphology. Positive parasite detections were found in 168 samples, yielding an overall percentage of positive fecal samples (%PFS) of 53.8%. The %PFS across the five provinces ranged from 42.5% to 63.5%. Among the positive fecal samples, the most frequently detected parasites were unidentified nematodes (38.1%), trichurid-like eggs (30.3%), strongyle-type eggs (25.0%), echinostome-like eggs (21.4%), and Ascaridia spp. (18.4%). Among the positive samples, small operculated trematode (SOT) and hymenolepidid-like eggs were detected in 3.0% and 1.2%, respectively; however, these findings may represent spurious passage. Single morphotype detection predominated, while co-detection of multiple morphotypes occurred less frequently. These findings document a diverse assemblage of intestinal parasite morphotypes in fecal samples from free-grazing ducks in northeastern Thailand, potentially reflecting exposure through aquatic and soil-associated routes.