Asymptomatic Blastocystis-infected Persons as Potential Carriers of Disease in Thailand

Aim: Blastocystis spp. is currently classified as a gastrointestinal protozoan parasite and has become quite a controversial organism. This study was aimed to obtain information about the prevalence of Blastocystis infection among an otherwise healthy, asymptomatic Thai population.

Study Design: Retrospective study.

Place and Duration of Study: The study areas were the Border Patrol-police station (Subdivision 12), Sa Kaeo Province; the Home for Mentally Handicapped Childcare, Ban Rajawadee, in Nonthaburi Province; Silpakorn University, Nakhon Pathom Province and the Intercity Motorway Division, Department of Highways, Bangkok. The study was carried during 2010-2013.

Methodology: Fecal examination was performed by direct simple smear test on 3,940 out of 6,537 Thais of different genders, ages, occupations, and residential locations who joined the annual health check-up program serviced by the Faculty of Tropical Medicine, Mahidol University.

Results: It was found that 1.0% (40/3,940) presented with Blastocystis infection was asymptomatic of clinical symptoms at a male to female ratio of 2.3:1.0. Blastocystis infection was predominantly found in the age group 41-50 years (47.5%, 19/40). Border Patrol-policemen (Subdivision 12), who resided and worked in rural areas of Sa Kaeo Province near the border between Thailand and Cambodia had significantly higher prevalence of Blastocystis infection (2.8%) than the staff of the Intercity Motorway Division, Department of Highways, in urban Bangkok (0.1%). Other occupations located in suburban areas, such as workers at the Home for Mentally Handicapped Childcare, Ban Rajawadee, in Nonthaburi Province, who worked closely with mentally handicapped children, and officials and lecturers at Silpakorn University, Nakhon Pathom Province, also had significantly higher prevalence rates than Intercity Motorway Division staff in urban Bangkok, with prevalence rates of 4.20% and 2.55%, respectively. Food handlers and cooks who prepared and sold food in Silpakorn University had similar prevalence rates of Blastocystis infection as Intercity Motorway Division staff.

Conclusion: This study revealed that Blastocystis infected patients probably did not show obviously clinical symptoms in asymptomatic carriers, who can spread infections to others and environments.