Background Giardia duodenalis is a common parasitic diarrheal agent in humans, especially in developing countries. The aim of this study was to investigate the prevalence and multilocus genetic characterization of G. duodenalis in patients with diarrhea and animals in northeastern China, and to assess the epidemiological role of animals in the transmission of human giardiasis. Methods A total of 1739 fecal specimens from 413 diarrheal patients and 1326 animals comprising 16 mammal species were collected in Heilongjiang Province of China and screened for G. duodenalis by PCR and sequencing of the SSU rRNA gene. All G. duodenalis-positive specimens were subtyped by PCR and sequencing of the bg, tpi, and gdh genes. To detect additional mixed infections of different assemblages, assemblage A/B/E-specific PCRs were performed to amplify the tpi gene. Results Sequence analysis of the SSU rRNA gene determined the prevalence of G. duodenalis (5.81%, 24/413) in diarrheal patients, with a peak in minors aged 5–17 years, and identified assemblages A and B. MLG-AII and MLG-B1 were obtained based on concatenated nucleotide sequences of the bg, tpi, and gdh genes, with MLG-AII being identical to a cat-derived isolate reported previously. By sequence analysis of the SSU rRNA gene, G. duodenalis was detected in 214 (16.14%) animals belonging to 11 mammal species, with the prevalence ranging from 1.69 to 53.85%, and assemblages A to G were identified. Sequence analysis of the bg, tpi, and gdh genes from 46 specimens produced 31 MLGs, including MLG-AI (n = 1), MLG-B2–B8 (n = 18), and MLG-E1–E23 (n = 27). Conclusions The finding of G. duodenalis in diarrheal patients enhances consciousness of detecting G. duodenalis in clinical practice and emphasizes the importance of health education in local inhabitants, especially in the age group of 5–17 years. The identification of seven assemblages (A to G) and 33 MLGs reveals genetic heterogeneity of G. duodenalis in the investigated areas. Due to insufficient homology data on the zoonotic transmission of G. duodenalis, the precise epidemiological role that animals play in the transmission of human giardiasis needs to be assessed by more large-scale molecular epidemiological investigations of local humans and animals. Graphical Abstract

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Background: Blastocystis is an enteric protozoan infecting humans and animals all over the world. Domestic animals play an important role in transmitting parasites to other domestic animals and humans. In the present study, a survey was conducted on Blastocystis among humans and domestic animals sharing habitats in northeastern China’ s Heilongjiang Province, in order to investigate the prevalence, the subtype distribution, as well as to evaluate the risk of the zoonotic transmission of Blastocystis isolates.Methods: A total of 314 (57 humans, 257 domestic animals) fecal samples were collected from 33 family households in three villages. The corresponding sequences of the barcode region of the SSU rRNA gene obtained in this study were subject to molecular analysis for subtype and allele identification of Blastocystis sp.Results: The prevalence of Blastocystis was 14.0% (8/57) in humans and 17.9% (46/257) in domestic animals. Eight PCR-positive human samples, 100% (8/8) were successfully subtyped, allowing the identification of the ST3, followed by ST1 and ST2. The 46 PCR-positive animal samples, 65.2% (30/46) were successfully subtyped, ST5 followed by ST1 in pigs, ST5 in goats; ST10, ST14 followed by ST3 in cattle; ST7 in chickens. Phylogenetic analysis showed that Blastocystis ST3 sequences from humans in two geographical locations formed two distinct clades. Alleles were identified using the Blastocystis 18S database and a total of 10 different alleles were found in six STs.Conclusions: The present study is the first description of the prevalence and subtype (allele) distribution of Blastocystis sp. by molecular analysis in humans and domestic animals in family units in China. Blastocystis ST2 in humans and ST5 in goats were reported in Heilongjiang Province for the first time. ST1 (a4) and ST3 (a34) overlaps were observed in humans and some domestic animal species (pig and cattle). The findings of potentially zoonotic subtypes in domestic animals suggest that these animals may serve as reservoirs of human Blastocystis sp. infections, thus help develop more efficient, targeted control strategies against human blastocystosis.