Geographic information system of Opisthorchis viverrini in northeast Thailand.

Background: Opisthorchiasis caused by Opisthorchis viverrini remains a major public health problem in many parts of Southeast Asia including Thailand, Lao PDR, Vietnam, and Cambodia. The epicenter of this disease is located in northeast Thailand, where high a prevalence of opisthorchiasis coexists with a high incidence of cholangiocarcinoma (CHCA), a major primary carcinoma of the liver with a very poor prognosis. Objective: Determine the surveillance characteristics of O. viverrini infections in northeast Thailand. Methods: Four thousand one hundred eighteen stool samples from 19 provinces were used in this study. All age groups were included, from below four years to more than 60 years. The geographic information system (GIS) was deployed to overlay the prevalence of disease on urban and agricultural areas as well as manmade land uses. Results: Results showed a rate of Opisthorchiasis of 20.39% (840/4,118). Farmland and forests (loam soil) were highly associated with infection. Conclusion: The rate of Opisthorchiasis is high in farmland and forests and lower in residential areas. Mass treatment targeted at high-risk areas may be a cost-effective control strategy and warrants further study.

Molecular typing of Vibrio cholerae O1 isolates from Thailand by pulsed-field gel electrophoresis.

The aim of the present study was to genotypically characterize Vibrio cholerae strains isolated from cholera patients in various provinces of Thailand. Two hundred and forty V. cholerae O1 strains, isolated from patients with cholera during two outbreaks, i.e. March 1999-April 2000 and December 2001-February 2002, in Thailand, were genotypically characterized by NotI digestion and pulsed-field gel electrophoresis (PFGE). In total, 17 PFGE banding patterns were found and grouped into four Dice-coefficient clusters (PF-I to PF-IV). The patterns of V. cholerae O1, El Tor reference strains from Australia, Peru, Romania, and the United States were different from the patterns of reference isolates from Asian countries, such as Bangladesh, India, and Thailand, indicating a close genetic relationship or clonal origin of the isolates in the same geographical region. The Asian reference strains, regardless of their biotypes and serogroups (classical O1, El Tor O1, O139, or O151), showed a genetic resemblance, but had different patterns from the strains collected during the two outbreaks in Thailand. Of 200 Ogawa strains collected during the first outbreak in Thailand, two patterns (clones)--PF-I and PF-II--predominated, while other isolates caused sporadic cases and were grouped together as pattern PF-III. PF-II also predominated during the second outbreak, but none of the 40 isolates (39 Inaba and 1 Ogawa) of the second outbreak had the pattern PF-I; a minority showed a new pattern--PF-IV, and others caused single cases, but were not groupable. In summary, this study documented the sustained appearance of the pathogenic V. cholerae O1 clone PF-II, the disappearance of clones PF-I and PF-III, and the emergence of new pathogenic clones during the two outbreaks of cholera. Data of the study on molecular characteristics of indigenous V. cholerae clinical isolates have public-health implications, not only for epidemic tracing of existing strains but also for the recognition of strains with new genotypes that may emerge in the future.

Prevalence of Strongyloides stercoralis infection in northeastern Thailand (agar plate culture detection).

The prevalence of Strongyloides stercoralis infection was studied in the rural and urban populations of 19 provinces of Northeastern Thailand. A total of 1233 fecal samples was collected from July to September 2002 and examined using agar plate culture method. The overall prevalence of S. stercoralis was 23.5 per cent with the highest infection rate in Kalasin Province (61.0%), predominantly among 60 year olds and older (28.0%), and in males (32.8%). The factors associated with Strongyloides infection were sex (males) and age (the over 19 year-old age group). CONCLUSION: S. stercoralis infection remains highly prevalent among the population of northeastern Thailand as confirmed by the agar plate culture method. The authors recommend that a program for effective strongyloidiasis control should have a justifiable priority.

Specific monoclonal antibodies to Strongyloides stercoralis: a potential diagnostic reagent for strongyloidiasis.

In this study, specific hybridomas secreting monoclonal antibodies (MAb) to antigen of Strongyloides stercoralis filariform larvae were produced. Specific epitopes targeted by the MAb were protein in nature and located in situ in the internal content of the filariform larvae of the parasite but not in the esophagus. The MAb reacted to the homologous antigen in an indirect ELISA but did not reveal any reaction to the SDS-PAGE separated-homologous antigen in a Western blot analysis (WB) suggesting a conformational epitope specificity. The MAb were of IgG1 isotype which is the isotype known to have high affinity to this epitope so they were used in a dot-ELISA to detect the antigen of the parasite. The assay could detect the epitopes in 78 ng or more of the crude filariform larval extract but did not reveal any positive result when applied to detect antigen in stool samples of parasitologically confirmed strongyloidiasis patients. The negative antigen test results can be explained as follows. Either the MAb were filariform stage-specific and thus did not recognize the rhabditiform larval antigen mainly contained in the patient's stool or the amounts of antigen in the stool samples were too small and/or unevenly dispersed. In the latter instance, the MAb developed in this study would have a diagnostic potential if used in an immunological test design where more volume of fresh stool sample could be accommodated in the test, e.g. a sandwich plate ELISA.