Parasitic Helminth Infections and Intron Sequence Genotyping of Opisthorchis viverrini-like Eggs in Outdoor Domestic Cats and Dogs Across the Chi River Basin, Maha Sarakham Province, Thailand

This study investigates the prevalence of parasitic helminths in free-ranging domestic cats and dogs near the Chi River and natural reservoirs in Maha Sarakham Province, Thailand. Fecal samples from 39 cats and 148 dogs were analyzed using a modified formalin-ether concentration technique (FECT). The overall prevalence of helminth infections was 64.1% in cats and 51.4% in dogs. Common parasites were detected including soil-transmitted species like <i>Ancylostoma</i> sp. (hookworm), <i>Toxocara</i> spp., and <i>Strongyloides</i> sp., as well as foodborne helminths such as <i>Taenia</i> sp., <i>Hymenolepis</i> sp., <i>Spirometra</i> sp., and <i>Opisthorchis</i> sp. Multiple parasitic infections were commonly found in dogs (57.9%) and cats (46.2%). Our findings suggest that domestic cats and dogs act as important reservoirs for zoonotic helminths in the region. Notably, <i>Opisthorchis viverrini</i>-like eggs were found exclusively in cats, with a prevalence of 23.1%. The intron 5 of domain 1 of the taurocyamine kinase gene (TkD1Int5) was used for genotyping <i>O. viverrini</i>-like eggs. All <i>O. viverrini</i>-like egg samples with TkD1Int5 haplotypes (Ov116-Ov123) were uniquely found in cats. Genetic analysis revealed that TkD1Int5 haplotypes were similar to those previously reported for <i>Opisthorchis viverrini</i> in various species of cyprinid fish across opisthorchiasis-endemic regions in Thailand and Lao PDR. Three TkD1Int5 haplogroups (I-III) were classified, with <i>O. viverrini</i>-like eggs from cats distributed across all haplogroups. Notably, one haplotype (Ov118) was genetically distinct from the others and did not cluster into any haplogroup. These findings highlight the crucial role of cats as reservoir hosts and their potential contribution to the transmission of the zoonotic liver fluke <i>O. viverrini</i>, posing a notable public health concern.