Abstract. A cross-sectional study was performed to determine the prevalence of giardiasis in hilltribe children of 2 different remote districts (Mae-chaem and Hod), Chiang Mai, Northern Thailand from November 2006-April 2007. The overall prevalence of giardiasis was 5.2%. Genetic characterization of Giardia duodenalis isolated from these children was performed using PCR methods specific for small subunit ribosomal rRNA (SSU-rRNA) and glutamate dehydrogenase (gdh) gene. This study shows that the distribution of Giardia assemblages varied in these 2 populations. Assemblage BIV was found predominantly in children from Hod District while assemblage AII was more common in children from Mae-Chaem District. Our result showed that assemblage A was significantly associated with loose/watery stool (p= 0.001). In addition, children harbouring assemblage B had shed a significantly higher number of cysts (p= 0.019) in stools than those infected with assemblage A. Further study on the epidemiology of giardiasis especially risk factors associated with genotyping would help to understand the nature of this disease in each population.

Objective: To investigate the incidence, spontaneous clearance, persistence and risk factors of Blastocystis infection in a rural community in Thailand. Methods: In February 2016, a cohort study was conducted in a rural community of Thailand. Baseline information of intestinal parasitic infections and follow-up visits were conducted. Blastocystis infection was detected in stool samples examined with short-term in vitro cultivation using Jones' medium supplemented with 10% horse serum. Participants were tested for Blastocystis infection at every study visit. Cox proportional hazard regression analysis was used to evaluate co-variates to determine the incidence of Blastocystis infection. Results: Of 733 enrolled participants, 57 (7.78%) were positive and 676 (92.22%) were negative for Blastocystis infection. All 676 participants were followed-up for Blastocystis infection between December 2016 and January 2018. In all, 52 of 482 cases (10.79%) comprised individual Blastocystis infection. The incidence density rates of Blastocystis infection, of spontaneous clearance of the disease and of persistent infection were 8.13, 63.14 and 38.70 per 1 000 person-months of follow-up, respectively. Our multivariate analysis revealed that opened defecation in fields or bushes (HR=4.8; 95% CI =2.1-10.4, P <0.001), raising cows (HR=2.8; 95% CI =1.1-7.1, P =0.032), not washing hands after animal contact (HR=2.1; 95% CI =1.0-4.2, P =0.044) and presenting symptoms of nausea or vomiting (HR=2.3; 95% C/=1.0-5.3, P =0.047) were predictive associated risks for the incidence of Blastocystis infection. Conclusions: Our study indicates that the best way to prevent Blastocystis infection can be by maintaining good personal hygiene, hand washing after animal contact and improving sanitary facilities.