Identification and genetic characterization ofContracaecumsp. (Nematoda: Anisakidae) from China

Contracaecumspecies are economically important fish-borne larval nematodes with zoonotic significance. In June 2019, more than 100 piscivorous birds died in their habitats close to the Wild Duck Lake, located in Yanqing, northwest of Beijing, China. Post-mortem examination of Black Night Herons (Nycticorax) revealed the presence of numerous anisakid nematodes in the proventriculus. Recovered nematodes were identified asContracaecumsp. based on morphological description. Phylogenetic analysis of the mitochondrial (mt) genome and the ITS gene showed that sequences ofContracaecumsp. Beijing isolates were grouped into a new individual cluster. Furthermore, the parasite was successfully isolated from fresh dead birds, feces of piscivorous birds, and fish and prevalence ranged from 8.0% to 81.8%. Consequently, our study demonstratedContracaecumsp. infections in different sources from China, which might constitute a threat to wildlife, aquaculture, and public health.