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| ABSTRACT |
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| INTRODUCTION |
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The epidemiology of these infections is still unclear in many aspects. It is assumed that these organisms are transmitted via the fecal-oral route since their spores are excreted via stool. A few studies showed the evidence supporting the role of person-to-person transmission in intestinal microsporidiosis.9,10 Thus, sources of the infection are apparently from those who excrete E. bieneusi spores both with and without diarrhea. Asymptomatic E. bieneusi infections were reported in a few studies,11,12 and could be one of the major sources of infections. Our surveys in a Thai orphanage located in Bangkok, Thailand found that E. bieneusi infection is common in this population (Mungthin M, unpublished data). Although these children usually had no gastrointestinal symptoms, monitoring of their infections will provide more epidemiologic information. In the present study, we conducted a cross-sectional study of E. bieneusi infection in these orphans to determine the prevalence and associated risk factors. In addition, genotypic characterization of E. bieneusi isolates from these orphans was also performed.
| MATERIALS AND METHODS |
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Genotypic characterization of E. bieneusi was determined by polymorphic sites on the internal transcribed spacer (ITS) region of the ribosomal RNA (rRNA) gene. This region was amplified by a polymerase chain reaction (PCR) using primers MSP3 (5'-GGAATTCACACCGCCCGTC(A/G) (C/T)TAT-3') and MSP4B (5'-CCAAGCTTATGCTTAAGTCCAGGGAG-3') as previously described.15 The specific primer pair amplifies 508-basepair fragment of E. bieneusi containing 122 basepairs of the 3' end of the small subunit rRNA gene, 243 basepairs of the ITS, and 143 basepairs of the 5' region of the large subunit rRNA gene. The PCR products were sent to Bioservice Unit in Bangkok, Thailand for DNA sequencing using a 3100 Genetic Analyzer (Applied Biosystems, Foster City, CA). Nucleotide sequences were determined with Sequencer program (Gene Codes Corporation, Inc., Ann Arbor, MI). The genotype of E. bieneusi from each specimen was confirmed by the homology of the sequenced PCR product to the published sequence in GenBank.
To determine the risk factors of E. bieneusi infection, standardized questionnaires concerning demographic data were used in this study. There were 10 small houses in this orphanage. Orphans positive for human immunodeficiency virus (HIV) lived in the same house, while HIV-negative orphans lived separately from the others. The child care providers of each house were asked to complete the questionnaires for each child. Significant differences among groups were assessed using the chi-square test with a 95% confidence interval (CI). Univariate analysis was performed using Epi-Info version 6.04b (Centers for Disease Control and Prevention, Atlanta, GA). Odds ratios with 95% CIs and P values were calculated to compare outcomes among study groups. Multivariate logistic regression using SPSS for Windows version 9.6 (SPSS, Inc., Chicago, IL) was performed for multivariate analysis to assess the independent association of the risk factors and E. bieneusi infections.
| RESULTS |
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The characteristics of the orphans enrolled in the study are shown in Table 1
. One HIV-positive child and 11 HIV-negative children between 14 and 33 months of age were positive for E. bieneusi. Significant differences were observed in the prevalence of E. bieneusi infections among different age groups and houses. The prevalence of E. bieneusi infections among HIV-positive and HIV-negative orphans was 2.6% (95% CI = 0.115.1%) and 4.4% (95% CI = 2.37.9%), respectively. None of the infected orphans had gastrointestinal symptoms during the surveys.
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| DISCUSSION |
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The high prevalence of the infection among children 1223 months old in this study was parallel to that in recent reports from Uganda18 and Thailand.17 This might be explained by the fact that their behavior is related to more active movement and more independent eating habits compared with those in the first year of age. Additionally, children in this age group still have poor toilet training and poor food-handling hygiene. The transmission via the fecal-oral route might explain the higher prevalence of the infection among orphans in the second year of age than among the infants in this facility. Although, our study was a cross-sectional evaluation, the data might indicate the possibility of self-limited E. bieneusi infection since the prevalence of the disease decreased after the second year of age. It is also possible that E. bieneusi persisted but was shed less consistently or at levels below detection in the older children.
An analysis of the ITS sequence of rDNA in E. bieneusi showed the polymorphisms that have been used for genotypic characterization. Although a variation of genotypes has been shown in other studies,1921 we found no variation of the genotype in this population. Compared with other study populations in Thailand, we found a wide variation of E. bieneusi genotypes in Thai HIV-positive patients (Subrungruang I, unpublished data). This might indicate that these children acquired the infection from the same source. Several studies have shown that different genotypes of E. bieneusi are prevalent in different populations. The occurrence of genotype A, as shown in this study, is also predominant in HIV-positive Peruvians with diarrhea.21
Major sources of the infections are apparently those both with and without diarrhea who excrete E. bieneusi spores. Thus, it is possible that E. bieneusi has been directly passed from one individual to another. A few studies provide evidence to support the role of person-to-person transmission in intestinal microsporidiosis. A case-control study in HIV-positive patients showed that male homosexuals had a greater risk of intestinal microsporidiosis.9 This finding suggested sexual transmission in the male homosexual group. Person-to-person transmission was also indicated in the study of E. bieneusi infection in HIV-positive patients in Zimbabwe.10 Those with a history of contact with diarrhea patients had a 1.9 times greater risk of getting the infection. In this study, the risk of E. bieneusi infection was independently greater in those orphans who lived in house no. 8. This house was designated to house newly admitted children for two weeks. If they remained healthy, they were then relocated to other houses. Children who needed medical care were also temporarily transferred to this house. Thus, these newly admitted children could be directly exposed to a source of infection. Our study also showed a significantly higher risk of acquiring the infection in this house. Multivariate analysis also showed that girls who lived here had a significantly higher risk of being infected than boys. Child care workers indicated that girls had a greater risk of being infected because they were more active and social than boys.
The evidence from this study suggests that infection with E. bieneusi in this orphanage is transmitted from person to person. Although these children were asymptomatic, they could be an unsuspected source of this infection for those who are susceptible. In an institution such as an orphanage where infection with E. bieneusi could spread easily, universal precautions should be taken since there are no specific prevention and control strategies for this infection.
Received October 11, 2004. Accepted for publication November 25, 2004.
Acknowledgments: We gratefully thank the director and childcare workers of the orphanage for their support of this study.
Financial support: This work was supported by the Phramongkutklao Research Fund and the Thailand-Tropical Diseases Research Program (T-2), ID 02-2-ARI-24-007.
* Address correspondence to Mathirut Mungthin, Department of Parasitology, Phramongkutklao College of Medicine, 315 Ratchawithi Road, Ratchathewi, Bangkok, 10400, Thailand. E-mail: mathirut{at}pmk.ac.th ![]()
Authors addresses: Saovanee Leelayoova, Tawee Naaglor, and Mathirut Mungthin, Department of Parasitology, Phramongkutklao College of Medicine, 315 Ratchawithi Road, Ratchathewi, Bangkok, 10400, Thailand, Telephone and Fax: 66-2-354-7761, E-mail: mathirut{at}pmk.ac.th. Ittisak Subrungruang and Porntip Chavalitshewinkoon-Petmitr, Department of Protozoology, Faculty of Tropical Medicine, Mahidol University, Bangkok, 10400 Thailand. Ram Rangsin, Department of Military and Community Medicine, Phramongkutklao College of Medicine, 315 Ratchawithi Road, Ratchathewi, Bangkok 10400, Thailand. Jeerapan Worapong, Center for Biotechnology and Department of Biotechnology, Institute of Science and Technology for Research and Development, Salaya, Nakornpratom 73170, Thailand.
| REFERENCES |
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