Prevalence of Intestinal Protozoan Infections Among Children in Thailand: a Large-Scale Screening and Comparative Study of Three Standard Detection Methods

High Prevalence of Protozoan Infections in Thailand

PREVALENCE OF INTESTINAL PROTOZOAN INFECTIONS AMONG CHILDREN IN THAILAND: A LARGE-SCALE SCREENING AND COMPARATIVE STUDY OF THREE STANDARD DETECTION METHODS

Vivornpun Sanprasert1,2, Nittaya Srichaipon2, Uthaitip Bunkasem1,2, Siriporn Srirungruang1,2 and Surang Nuchprayoon1,2

1Department of Parasitology, 2Lymphatic Filariasis and Tropical Medicine Research Unit, Chulalongkorn Medical Research Center, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand

Abstract. A significant impact of intestinal parasitic infections on public health has mostly been neglected. Parasitic infections are one of risk factors for malnutrition in children. In this study, a large-scale screening of intestinal parasitic infections among children in 16 schools in 6 regions of Thailand was performed. In addition, we compared sensitivity of methods currently employed for detection of intestinal parasitic infection. Fecal samples collected from 1,909 students were examined for intestinal parasites by simple smear, formalin-ethyl acetate concentration (FECT), and Locke-egg-serum (LES) medium culture methods. Seven hundred and thirteen samples were infected with at least one intestinal parasite. The highest prevalence (82.8%) was found in Kanchanaburi Province, western Thailand. Blastocystis spp was the most common (32.8%) parasite, fol- lowed by Giardia duodenalis (4.2%), Ascaris lumbricoides (3.6%), hookworms (1.6%), Entamoeba histolytica (0.7%), Trichuris trichiura (0.5%), Enterobius vermicularis (0.5%), Strongyloides stercoralis (0.4%), minute intestinal flukes (0.2%), and Taenia spp (0.1%). Mixed parasitic infections were found in 121 students. In a comparative study, we found that FECT was more sensitive (74.0%) than simple smear (55.0%) method for detecting helminths. However, sensitivity of these two methods is not significantly different for protozoan detection (31.2% by simple smear and 33.5% by FECT). LES culture technique was the most sensitive method (77.5%) for detecting Blastocystis spp. Our results indicate a high prevalence of intestinal parasite infection among Thai students. More sensitive methods should be developed for a large-scale screening of intestinal protozoan infection. Keywords: Blastocystis spp, intestinal parasite, school-age student, Thailand

INTRODUCTION Correspondence: Surang Nuchprayoon, De- partment of Parasitology, Faculty of Medicine, Parasitic infection remains a major Chulalongkorn University, Bangkok 10330, public health problem worldwide, partic- Thailand. ularly in developing countries. However, Tel: +66 (0) 2256 4387, +66 (0) 2252 5944; Fax: the impact of these infections on public +66 (0) 2252 4963 health has been mostly ignored. To date, a E-mail: [email protected] national prevalence of intestinal parasites

Vol 47 No. 6 November 2016 1123 Southeast Asian J Trop Med Public Health in Thailand has not been reported. Most Walker et al, 2007; Jardim-Botelho et al, studies report prevalence in specific areas. 2008; Yentur Doni et al, 2015). In Thailand, In 2009, the national survey of helminthia- the studies of intestinal parasite infec- sis in Thailand showed high prevalence tions usually report only the prevalence of parasitic infection (18.1%) in Thai of certain parasites (eg, soil-transmitted people (Wongsaroj et al, 2012). Prevalence helminths) (Anantaphruti et al, 2008), or in of intestinal parasitic infections varies a selected group of children in certain areas from one area to another depending on (eg, in orphanages and in students in cen- the degree of personal and community tral region of the country) (Saksirisampant hygiene, sanitation and climatic factors et al, 2003, 2006; Ngrenngarmlert et al, 2007). (Soriano et al, 2001; Manganelli et al, 2012; Effective diagnosis will assist in a bet- Wongsaroj et al, 2012; Boonjaraspinyo et al, ter surveillance of intestinal parasitic infec- 2013). Prevalence of intestinal parasitic tions. Early diagnosis is needed to reduce infections among Thai patients in urban and prevent transmission. There are many areas who visited the outpatient unit of alternative methods to detect parasitic King Chulalongkorn Memorial Hospi- infections, including molecular and im- tal, Bangkok is 6.1-8.94% (Nuchprayoon munological assays. However, these tech- et al, 2002; Saksirisampant et al, 2002). niques are time-consuming and require This prevalence is lower than the aver- expensive reagents, instruments, as well as age prevalence (34-72%) in remote areas technical expertise. Thus, microscopic ex- of Thailand (Triteeraprapab et al, 1997; amination remains the routine method for Triteeraprapab and Nuchprayoon, 1998; laboratory diagnosis of intestinal parasitic Triteeraprapab et al, 1999; Nuchprayoon infection. The current routine techniques et al, 2009). This may be due to the fact for screening intestinal parasitic infec- that people in remote areas usually have tion are simple smear and formalin-ethyl cultural food beliefs, poor dietary habit, acetate concentration (FECT). The simple poor sanitation and hygiene as well as smear technique is easy to perform but its difficulty in gaining access to good health sensitivity is low, leading to misdiagnosis. information and healthcare services. Sensitivity of FECT is higher than simple Parasitic infection in children are still smear technique for diagnosis of intestinal common, even in developed countries. helminth infection (Saksirisampant et al, Globally, over 1 billion people are esti- 2003; Nuchprayoon et al, 2009; Hailu and mated to be infected with at least one type Abera, 2015). of intestinal helminths, with the highest In this study, a large-scale survey prevalence in school-age children (de Silva of the prevalence of intestinal parasitic et al, 2003). Parasitic infection can lead to infection in school-age children was per- malabsorption and chronic blood loss in formed in 6 regions of Thailand. In addi- children, with long-term effects on their tion, a comparative study was conducted physical (height and weight) and cogni- among different techniques for parasite tive development. Malnutrition is com- identification. mon in school-age children in developing countries. Parasitic infection is one of risk MATERIALS AND METHODS factors for malnutrition, poor psychomotor development, growth retardation, and Study areas and test population stunting in children (Casapia et al, 2006; Cross-sectional surveys were per-

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parasitic diseases (eg, consumption of well-cooked food, hygienic defecation and no bare-feet be- havior) also were explained to the participants. Written in- formed consent was obtained from legal guardian of each in- dividual to partici- pate in the study. Stool examination Stool collection containers were dis- tributed to all participants. In order to avoid contamina- tion, specific precau- Fig 1 - Location of the study areas in the six regions of Thailand. tion and guideline for specimen collec- formed in 16 schools in 7 provinces (Ang tion were explained to all students. Stool Thong, Nakhon Ratchasima, Khon Kaen, samples were stored at room temperature Nan, Chon Buri, Kanchanaburi and Phat- prior to cultivation and stool examina- thalung) located in central, northeastern, tions on the following day at Lymphatic northern, eastern, western, and southern Filariasis and Tropical Medicine Research Thailand (Fig 1). All schools, except those Unit, Department of Parasitology, Faculty in Nakhon Ratchasima Province, are in of Medicine, Chulalongkorn University, rural areas. Schools in Nan and Kanchana- Bangkok. Simple smear, FECT and Boeck buri Provinces are located in mountain and Drbohlav’s Locke-egg-serum (LES) villages and most of students are from medium culture techniques for detec- hill tribes. A number of students in Chon tion of intestinal parasite eggs or larvae Buri and Kanchanaburi Provinces are were performed as described previously migrants from Myanmar. In cooperation (Nuchprayoon et al, 2009). In brief, stool with school directors, 1,909 students aged samples were examined microscopically between 1 to 23 years (mean ± range, 9.9 of simple smears using normal saline ± 4.9 years) were recruited to the study. and iodine preparation. About 2-5 mg The study was approved by the Eth- of each stool specimen was processed by ics Committee of the Faculty of Medicine, FECT method. LES medium culture was Chulalongkorn University, Bangkok (IRB conducted for identification ofBlastocystis no. 396/56). All subjects were well in- sp and Entamoeba histolytica. The presence formed about the health effects and the of intestinal parasite eggs, larvae or cysts danger from intestinal parasitic infection. was determined microscopically. Samples Prevention methods against common were independently examined by two

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Table 1 Prevalence of intestinal parasitic infections among surveyed students in Thailand classified by gender and age groups.

Age Number Number of positives Percent prevalence (years) (male, female, unspecified) (male, female, unspecified) (male, female, unspecified)

1-6 278 (145, 133, 0) 79 (43, 36, 0) 28.4 (29.7, 27.1, 0) 7-12 1,193 (551, 642,0) 555 (261, 294, 0) 46.5a (47.4, 45.8, 0) 13-23 403 (207, 196, 0) 71 (29, 42, 0) 17.6 (14.0, 21.4, 0) Not available 35 (0, 0, 35) 8 (0, 0, 8) 22.9 (0, 0, 22.9) Total 1,909 (903, 971, 35) 713 (333, 372, 8) 37.3 (36.9, 38.3, 22.9) aSignificantly higher than other age groups p( < 0.005).

examiners. Individuals infected with parasitic infection was found among stu- pathogenic parasites were treated with dents in Nakhon Ratchasima (0.5%) and standard drug regimens. the highest in Kanchanaburi (82.8%) (p < Data analysis 0.001) (Table 2). Prevalence in Ang Thong, Chon Buri, Phattalung, Khon Kaen, and Data were analyzed using Microsoft Nan Province was 14.5%, 23.9%, 41.0%, Excel 2010 program and GraphPad Prism 43.6%, and 54.6%, respectively. version 5.01 for Windows. Numerical data are presented as mean ± SD. Association The most commonly identified para- between population groups was analyzed site was Blastocystis spp (32.8%) (Table 2). using chi-square or Fisher exact test. A Other protozoan infections were Giardia p-value < 0.05 is considered statistically duodenalis (4.2%) and E. histolytica (0.7%). significant. Nematode infections were Ascaris lumbricoides (3.6%), hookworm (1.6%), Strongy- RESULTS loides stercoralis (0.4%), Trichuris trichiura (0.5%), and Enterobius vermicularis (0.5%). Prevalence of intestinal parasitic infection A trematode (minute intestinal fluke) in school-age students (0.2%) and a cestode (Taenia spp) (0.1%) Out of 1,909 participants, 713 (37.3%) also were detected. students (333 males, 372 females and 8 un- Classified according to route of trans- specified) were infected with at least one mission, the majority (88.1%) of infected kind of intestinal parasite (Table 1). No students had parasites transmitted by statistically significant difference between fecal-oral route (ie, Blastocystis spp, G. duo- prevalence of intestinal parasitic infec- denalis, E. histolytica, and E. vermicularis) tion was found among genders (36.9% (Table 2). Soil-transmitted helminthes (ie, in males, 38.3% in females and 22.9% in A. lumbricoides, T. trichiura, S. stercoralis, unspecified subjects) p( = 0.164) (Table 1). and hookworms) were found in 16.3% of The highest prevalence of intestinal para- students, while food-borne parasites (ie, sitic infection was found in students aged minute intestinal fluke and Taenia spp) 7-12 years old (46.5%) (p < 0.001). were present in 0.7% of these students. The lowest prevalence of intestinal Non-pathogenic protozoa, Entamoeba

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; - coli, Entamoeba nana, Trichomonas spp; 0 0 0 0 0 0 1 hominis and Iodamoeba butschlii, Tn

1 (0.1) also were detected with preva- Taenia lence of 6.3%, 3.9%, 0.2%, and 0 0 0 0 0 0 4 Tn, Mn 0.1%, respectively (Table 3).

; 4 (0.2) Of the 713 infected indi- Entamoeba histolytica Entamoeba 2 0 0 viduals, 121 (17.0%) students had Ev

10 (0.5) mixed parasitic infections: 86.8% with two species of intestinal spp; Eh, 4 0 0 0 2 0 2 1 4 5

Tt parasites, 11.5% with three species

10 (0.5) and 1.7% with 4 species (Table 4). Blastocystis spp and G. duodenalis Strongyloides stercoralis Strongyloides 2 0 0 Ss Blastocystis constituted the most common 7 (0.4) mixed infections (38.8%), fol- ; Bh, lowed by Blastocystis spp and 0 0 1 2 1 8 4 1 9 2

Hw A. lumbricoides (29.0%) (data not 30 (1.6) shown). 4 7 0 0 1 0 1 Al 63 Comparative study of the different

69 (3.6) techniques for parasite detection Ascaris lumbricoides

Pathogenic parasite (prevalence) A comparison between sim- 0 0 2 6 0 0 Eh ple smear and FECT methods 14 (0.7) revealed no significant difference Mn, minute intestinal fluke; Ss,

0 Table 2 Table < 0.005). in sensitivity of parasite detection 45 6 14 Gd p

81 (4.2) (41.7% vs 46.4%) (Table 5). How- ever, for detection of helminth 1 80 2 26 54 8

Bh infection FECT method was sig- 215 105 7 145 5 nificantly more sensitive (74.0%) 626 (32.8) than simple smear (55.0%) (p < ; Hw, hookworm; ; Hw,

a 0.001). Moreover, FECT recov- ered considerably more eggs and

(0.5) (43.6) (54.6) (82.8) (14.5) (41.0) (23.9) (37.3) larvae of helminths than simple 1 82 48 79

positives smear method (data not shown). 131 222 150 713 Number of Interestingly, simple smear was prevalence) (percent Giardia duodenalis Giardia more sensitive than FECT technique in detecting A. lumbricoides Gd,

;

eggs (87% vs 62%) (Table 5). For 187 188 240 268 330 366 330 Significantly higher than other provinces ( Significantly higher than other provinces 1,909 protozoan detection, no signifi- a

Number

. cant difference in sensitivity was discerned between overall simple smear (31.2%) and FECT (33.5%) method (p = 0.19). However, FECT technique was superior to simple

Enterobius vermicularis Enterobius smear method for detecting G. Prevalence of intestinal parasitic infections among surveyed students classified by parasites and province in Thailand. in province and parasites by classified students surveyed among infections parasitic intestinal of Prevalence Trichuris trichiura Trichuris

in Thailand Province in Kaen Nakhon Ratchasima Khon Nan Kanchanaburi Buri Ang Thong Phatthalung Chon Total duodenalis (61.7% vs 46.9%). Ev, Ev, The total number of infected individuals detected by each technique is not equal to the sum AL, of parasite. infected one than individuals more with with infections each mixed have parasite subjects some be cause Tt,

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Table 3 Prevalence of non-pathogenic protozoan infections among surveyed students classified by parasite and province in Thailand.

Province Number Number of Non-pathogenic parasite positives (percent prevalence) (percent prevalence) Ec En Th Ib Nakhon Ratchasima 187 1 (0.5) 1 0 0 0 Khon Kaen 188 10 (5.3) 4 5 2 0 Nan 240 22 (9.2) 22 0 0 0 Kanchanaburi 268 70 (26.1) 54 31 1 1 Ang Thong 330 17 (5.2) 13 4 0 0 Phatthalung 366 21 (5.7) 11 9 1 0 Chon Buri 330 35 (10.6) 15 25 0 0 Total 1,909 176 (9.2) 120 (6.3) 74 (3.9) 4 (0.2) 1 (0.1)

EC, Entamoeba coli; En, Endolimax nana; Ib, Iodamoeba butschlii; Th, Trichomonas hominis.

Table 4 Mixed infections of the intestinal parasites among surveyed students in Thailand.

Parasitic infection Number of positives (%) (N = 1,909)

Single infection 592 (83.0) Mixed infections 121 (17.0) 2 types of parasites 105 (86.8)a 3 types of parasites 14 (11.5) 4 types of parasites 2 (1.7) Total 713 (37.3) aSignificantly higher than other mixed parasite infections (p < 0.05).

To compare the sensitivity of sample be detected by LES culture. Comparison smear and FECT procedures with that of of the sensitivity of the three techniques concentration techniques with LES cul- employed in this study is summarized by ture, only Blastocystis spp and E. histolytica a Venn diagram (Fig 2). were cultivable. Only 1,001/1,909 stool samples were of sufficient quantity to be DISCUSSION used for all three techniques. LES culture has the highest sensitivity for protozoan In this study, we performed a large- detection (82.9%), compared with 28.9% scale screening of intestinal parasitic infec- by simple smear and 27.7% by FECT tion among 1,909 students in 6 regions of techniques. Only 49 (8.4%) students were Thailand. We found a high (37.3%) preva- positive by all three tests. Interestingly, lence of infection among the students. Our 53.5% of infected individuals could only data agreed with several studies, which

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N=1,001 prevalence of protozoan than helminth infection. This may be due to the annual treatment of helminth infection by mebenda- zole in some families and mass treatment in some villages. How- ever, the diagnosis and treatments of protozoan infection have usually been ignored. There is no report of clinical manifestations Fig 2–Venn diagram showing patterns of detection of protozoa by of these affected stu- simple smear (Simple), formalin-ethyl acetate concentration dents. However, in- (FECT) and Boeck and Drbohlav’s Locke-egg-serum (LES) testinal protozoan and medium culture methods. Number in circle indicate number of helminth infections positive samples. Number in parenthesis indicate sensitivity of have been shown to each technique for protozoan identification. N = total number have significant as- of samples examined. sociation with growth retardation and poor showed that intestinal parasitic infections psychomotor development of children are common (4.2-48.9%) among children (Yentur Doni et al, 2015). Therefore, sur- in Thailand (Piangjai et al, 2003; Saksiri- veillance of intestinal protozoan infection sampant et al, 2006; Ngrenngarmlert et al, should be emphasized in the country’s 2007; Kitvatanachai and Rhongbutsri, public health programs. 2013). The prevalence in children is much The most common parasites found higher than in adults (6.1%) (Saksirisam- in this study were Blastocystis spp and G. pant et al, 2002), but still lower than in im- duodenalis. Less than 10% of students were migrant (81.1%) and Thai children (71.0%) infected with non-pathogenic protozoa (E. in orphanages (Saksirisampant et al, 2003; nana, E. coli, T. hominis, and I. butschlii). Sagnuankiat et al, 2016). This may be due These findings imply that poor sanitation to the overcrowded environment and poor exists among school-age children in rural sanitation in orphanages. areas. Blastocystis spp and G. duodenalis The common parasites identified are commonly found in water supplies, in children in Thailand are T. trichiura especially ponds and canals (Khalifa et al, (0.19-50.8%), E. vermicularis (0.19-25.2%), 2014). These parasites were detected with hookworms (0.19-11.6%), A. lumbricoi- high prevalence in Nan and Kanchanaburi des (9.8-15.3%), S. stercoralis (0.92%), Provinces. Schools we studied are located Blastocystis spp (0.19-0.5%), and G. duo- in mountain villages. Water supplies used denalis (1.25-10.2%) (Saksirisampant et in these areas are from mountain sources. al, 2004, 2006; Sagnuankiat et al, 2016). Thus, contaminated water supplies might On the other hand, we found a higher be the importance source of these pro-

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Table 5 Comparison of sensitivity of two techniques for parasite identification.

Parasite Number Number of positives (%) (percent sensitivity)

Simple smear Formalin-ethyl acetate method concentration method

Helminth Taenia spp 1 (0.1) 0 1 (100) E. vermicularis 10 (1.4) 5 (50.0) 7 (70.0) T. trichiura 10 (1.4) 1 (10.0) 9 (90.0) Hookworms 30 (4.2) 3 (10.0) 26 (86.7) A. lumbricoides 69 (9.7) 60 (87.0) 43 (62.3) S. stercoralis 7 (1.0) 3 (42.9) 7 (100) Minute intestinal flukes 4 (0.6) 0 4 (100) Total 131 72 (55.0) 97 (74.0) Protozoa G. duodenalis 81 (11.4) 38 (46.9) 50 (61.7) E. histolytica 14 (2.0) 9 (64.3) 7 (50.0) Blastocystis spp 626 (87.8) 178 (28.4) 177 (28.3) Total 721 225 (31.2) 234 (33.5) Total 713 297 (41.7) 331 (46.4)

The total number of infected individuals detected by each technique is not equal to the sum of infected individuals with each parasite because some subjects have mixed infections with more than one parasite.

tozoa infections. Water treatment was denalis (16.8%). The major risk factor for reported to be associated with reduction infection with these parasites is drinking of some protozoan infections, including water from mountain sources contaminat- Blastocystis spp and G. duodenalis (Speich ed with infective stages of the parasites. et al, 2016). In the northern region, prevalence of The prevalence of intestinal parasite parasitic infection was 54.6%, not differ- infection in each region of Thailand was ent from previous reports (37-72%) (Tri- significantly different. The reasons for teeraprapab et al, 1997; Triteeraprapab and this may be directly related to specific Nuchprayoon, 1998; Triteeraprapab et al, geographic characteristics, as well as to 1999; Piangjai et al, 2003; Nuchprayoon et ecological, sanitary, socioeconomic, and al, 2009). The high prevalence of Blastocys- cultural factors (Soriano et al, 2001; Sin- tis spp (43.8%) and A. lumbricoides (26.3%) niah et al, 2014). The highest prevalence were similar to those of Kanchanaburi (82.8%) of intestinal parasitic infection Province. The majority of infected stu- was found in Kanchanaburi Province lo- dents in Nan were from hill tribes, where cated in the western region of Thailand. sanitation is poor and water supplies are Common parasites found in this region from mountain sources. Moreover, hill were Blastocystis spp (80.2%) and G. duo- tribes in northern regions usually live in

1130 Vol 47 No. 6 November 2016 High Prevalence of Protozoan Infections in Thailand house raised on stilts and keep domestic Organization for northeastern Thailand animals, such as pig and chicken, under (WHO, 1997). their houses. Cesspools are usually out- In the comparative study of standard side the house. Manure made from human detection techniques, we found sensitiv- and animal waste is used in the fields. It ity of FECT not different from simple is not unexpected that we found a high smear method for diagnosis of intestinal prevalence of A. lumbricoides infection in parasitic infection. However, FECT was this region. In one of the schools surveyed more sensitive than simple smear method 90% of stool samples contained A. lumbri- for detection of helminth infection. For coides (data not shown). Zoonotic A. suum protozoan detection, no significant differ- should also be of concern. Although the ence was found between overall sensitiv- majority of students did not wear shoes, ity of simple smear and FECT methods. we found low prevalence (0.8%) of hook- However, FECT had better sensitivity for worms. detecting G. duodenalis than simple smear In northeastern region, we surveyed method. LES culture had the highest sen- Nakhon Ratchasima and Khon Kaen sitivity for detecting Blastocystis spp and Provinces and found lower prevalence E. histolytica. Although cultivation of lu- of intestinal parasites (22.1%) compared minal protozoa is usually performed in re- to other previous studies (6.22-37.2%) search laboratories (Clark and Diamond, (Kitvatanachai et al, 2008; Boonjaraspinyo 2002), cultivation of protozoa might be et al, 2013; Kaewpitoon et al, 2015). The useful for the detection of intestinal pro- prevalence rate of intestinal parasitic tozoan infection. Our results showed that infections was significantly higher in Blastocystis spp and E. histolytica infections Khon Kaen (43.6%) compared to Nakhon were detected only by the LES medium Ratchasima Province (0.5%). Only one culture. Our data suggest that the simple student in Nakhon Ratchasima Province smear technique is insufficiently sensitive was infected with Blastocystis spp. Rea- to be used alone for screening of parasitic sons for this difference might be difference infections. in sanitary conditions and socioeconomic Improvements in sanitation, personal factors. In contrast to students in Khon hygiene, quality of water supplies, as well Kaen Province, the school we surveyed in as basic health education are needed if Nakhon Ratchasima Province is a primary intestinal parasitic infections are to be school in a barrack in an urban area. The reduced among children in Thailand. environment in the school is clean. From Moreover, surveillance of the sources of the questionnaire, we observed that fam- protozoan infection particular to each ily status of all students in Nakhon Rat- area, such as protozoa in water supplies chasima Province is quite high. and in animals, should be conducted Interestingly, we found O. viverrini with appropriate methods with higher infection (normally found in northeastern sensitivity. region) in four students, 6-9 years old, in Chon Buri Province located in western ACKNOWLEDGEMENTS region (data not shown). The prevalence of O. viverrini infection among this age The authors thank the National Re- group was 1.5%, slightly higher than a search Council of Thailand (NRCT) for previous report (1.2%) of the World Health support of the project, directors and teach-

Vol 47 No. 6 November 2016 1131 Southeast Asian J Trop Med Public Health ers at all schools for their participation, cross-sectional survey of intestinal helmin- and Ms Rungfar Boonserm, Ms Panutda thiases in rural communities of Nakhon Chantanoi, Ms Narumol Chaipat and Ms Ratchasima province, Thailand. J Med As- Ratree Choo-on and staff of the Lymphatic soc Thai 2015; 98 (suppl 4): S27-32. Filariasis and Tropical Medicine Research Khalifa RM, Ahmad AK, Abdel-Hafeez EH, Unit, Department of Parasitology, Faculty Mosllem FA. Present status of protozoan of Medicine, Chulalongkorn University pathogens causing water-borne disease for technical assistance. in northern part of El-Minia Governorate, Egypt. J Egypt Soc Parasitol 2014; 44: 559-66. REFERENCES Kitvatanachai S, Boonslip S, Watanasatitarpa S. Intestinal parasitic infections in Srimum Anantaphruti MT, Waikagul J, Maipanich W, suburban area of Nakhon Ratchasima et al. School-based health education for the Province, Thailand. Trop Biomed 2008; 25: control of soil-transmitted helminthiases 237-42. in Kanchanaburi province, Thailand. Ann Kitvatanachai S, Rhongbutsri P. Intestinal Trop Med Parasitol 2008; 102: 521-8. parasitic infections in suburban govern- Boonjaraspinyo S, Boonmars T, Kaewsamut B, ment schools, Lak Hok subdistrict, Muang et al. A cross-sectional study on intestinal Pathum Thani, Thailand. Asian Pac J Trop parasitic infections in rural communities, Biomed 2013; 6: 699-702. northeast Thailand. Korean J Parasitol 2013; Manganelli L, Berrilli F, Di Cave D, et al. In- 51: 727-34. testinal parasite infections in immigrant Casapia M, Joseph SA, Nunez C, Rahme E, children in the city of Rome, related risk Gyorkos TW. Parasite risk factors for stunt- factors and possible impact on nutritional ing in grade 5 students in a community status. Parasit Vectors 2012; 5: 265. of extreme poverty in Peru. Int J Parasitol Ngrenngarmlert W, Lamom C, Pasuralertsu- 2006; 36: 741-7. kul S, et al. Intestinal parasitic infections Clark CG, Diamond LS. Methods for cultiva- among school children in Thailand. Trop tion of luminal parasitic protists of clinical Biomed 2007; 24: 83-8. importance. Clin Microbiol Rev 2002; 15: Nuchprayoon S, Sanprasert V, Kaewzaithim S, 329-41. Saksirisampant W. Screening for intesti- de Silva NR, Brokker S, Hotez PJ, Montresor nal parasitic infections among Myanmar A, Engles D, Savioli L. Soil-transmitted migrant workers in Thai food industry: helmint infectious: updating the global a high-risk transmission. J Immigr Minor picture. Trends Parasitol 2003; 19: 547-51. Health 2009; 11: 115-21. Hailu T, Abera B. Performance evaluation of Nuchprayoon S, Siriyasatien P, Kraivichian K, direct saline stool microscopy, formol ether Porksakorn C, Nuchprayoon I. Prevalence concentration and Kato Katz diagnostic of parasitic infections among Thai patients methods for intestinal parasitosis in the at the King Chulalongkorn Memorial Hos- absence of gold standard methods. Trop pital, Bangkok, Thailand. J Med Assoc Thai Doct 2015; 45: 178-82. 2002; 85 (suppl 1): S415-23. Jardim-Botelho A, Brooker S, Geiger SM, et al. Piangjai S, Sukontason K, Sukontason KL. Age patterns in undernutrition and hel- Intestinal parasitic infections in hill-tribe minth infection in a rural area of Brazil: as- schoolchildren in Chiang Mai, northern sociations with ascariasis and hookworm. Thailand. Southeast Asian J Trop Med Public Trop Med Int Health 2008; 13: 458-67. Health 2003; 34 (suppl 2): 90-3. Kaewpitoon SJ, Loyd RA, Kaewpitoon N. A Sagnuankiat S, Wanichsuwan M, Bhunnachet E,

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