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 Ancylostoma sp. (hookworm), Toxocara spp., and Strongyloides sp., as well as foodborne helminths such as Taenia sp., Hymenolepis sp., Spirometra sp., and Opisthorchis 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, Opisthorchis viverrini-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 O. viverrini-like eggs. All O. viverrini-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 Opisthorchis viverrini in various species of cyprinid fish across opisthorchiasis-endemic regions in Thailand and Lao PDR. Three TkD1Int5 haplogroups (I–III) were classified, with O. viverrini-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 O. viverrini, posing a notable public health concern.

Blood-borne parasites, including Babesia spp., Theileria spp., and Anaplasma spp., pose significant threats to buffalo health and productivity, highlighting the need for continuous epidemiological surveillance in endemic regions such as Thailand. This study aimed to investigate the molecular prevalence of hemoparasites and characterize the genetic diversity of Theileria orientalis in swamp buffaloes from Northeast Thailand. A total of 176 blood samples were analyzed using genus- and species-specific PCR assays. Samples positive for T. orientalis were subjected to DNA sequencing of the MPSP gene, followed by haplotype and phylogenetic analyses. Overall, 19.3% (95% CI: 13.8–25.9) of samples were positive for at least one hemoparasite. The prevalence of T. orientalis, Babesia bigemina, and B. bovis was 15.9%, 3.4%, and 2.3%, respectively. Notably, all B. bovis infections occurred as co-infections with T. orientalis. Anaplasma spp. showed the lowest prevalence (1.7%), comprising A. marginale 0.6% and A. platys 1.1%. Sequence analysis of T. orientalis revealed significant genetic diversity within the population. Subsequent phylogenetic and pairwise distance analyses identified four distinct genotypes including Type 7, which was found to be predominant, followed by Type 5, Type N2 and Type 4. This study provides molecular evidence of hemoparasite infections and highlights the complex genetic diversity of T. orientalis in Thai water buffaloes. The co-circulation of multiple genotypes and co-infections underscore the need for improved epidemiological monitoring and targeted control strategies in the region.