Cyclospora in humans, animals, fresh produce and water in China: implications for host specificity of Cyclospora species and zoonotic transmission of C. cayetanensis

Abstract Cyclospora spp. are common protozoan parasites that primarily colonize the small intestines of humans and some animals, causing diarrhea and gastroenteritis. To date, 22 Cyclospora species have been identified, with C. cayetanensis being the cause of cyclosporiasis in humans worldwide. Domestic animals, particularly cattle, as well as some wildlife, have been identified as hosts for Cyclospora spp., and putative C. cayetanensis infections have been documented in animals. These findings raise concerns about the host specificity of Cyclospora spp. and the risk of zoonotic transmission of C. cayetanensis . In this report, we review the molecular epidemiology of cyclosporiasis in humans and animals in China. To date, C. cayetanensis infection is endemic in China, with its prevalence influenced by factors such as residence, season, and the clinical and immune status of the host. Molecular genetic analysis reveals that the genotypes of C. cayetanensis infecting humans in China exhibit distinct region-specific genetic characteristics, likely due to geographic isolation. In contrast, nonhuman primates are commonly infected with host-specific Cyclospora spp., with C. macacae most often identified in macaque monkeys. Notably, misidentification of Cyclospora in animal samples has been observed in multiple domestic studies. The Cyclospora -like parasite identified in cattle in several studies is likely a misidentification of Eimeria subspherica , as suggested by comparisons of morphometric and sequence data from isolates in China and Japan. Similarly, the identification of C. cayetanensis in animals (cattle, foxes, minks, raccoon dogs, and snakes) in several reports is mostly based on PCR analysis and is not supported by careful reanalysis of the SSU rRNA sequences. These erroneous reports not only lead to an overestimation of the zoonotic transmission potential of C. cayetanensis , but also obscure the true transmission risks posed by different Cyclospora species. Accordingly, we have recommended several procedures to reduce the misidentification of Cyclospora spp. in animals in future studies. These procedures include using microscopy and multilocus sequence analysis for confirmatory diagnoses and using valid reference sequences from both Cyclospora and Eimeria for direct comparisons and phylogenetic analyses of SSU rRNA sequences. They would reduce the current confusion surrounding the host specificity of Cyclospora species and the zoonotic potential of C. cayetanensis .