MaxEnt modeling of soil-transmitted helminth infection distributions in Thailand.

Infections due to soil-transmitted helminths (STHs), i.e. Ascaris lumbricoides, Trichuris trichiura, hookworms, and Strongyloides stercoralis, are widely distributed in tropical and subtropical areas in which approximately 1.5 billion people are infected. A clear understanding of the epidemiology and distribution of diseases is an important aid for control and prevention. The aim of our study was to identify the effects of environmental and climatic factors on distribution patterns of STHs and to develop a risk map for STH infections under current environmental and climate regimes in Thailand. Geographical information systems (GIS), remote sensing, and Maximum Entropy (MaxEnt) algorithm software were used to determine the significant factors and to create predictive risk maps for STH infections in Thailand. The disease data from Thailand covered the years from 1969 to 2014, while environmental and climatic data were compiled from the Worldclim database, MODIS satellite imagery, Soilgrids and ISCGM. The models predicted that STHs occur mainly in southern Thailand. Mean annual precipitation was the factor most affecting the current distribution of A. lumbricoides, T. trichiura, and S. stercoralis. Land cover class was the main predictor for distribution of S. stercoralis and important for hookworms. Altitude was the dominant factor affecting the distribution of hookworms, and mean temperature of the wettest quarter was significantly associated with A. lumbricoides distribution. A predicted distribution map of STHs to identify environmental risk factors in Thailand is presented. This work provides a model for use in STH monitoring and health planning not only in Thailand but also in other countries with similar disease conditions.

Health informatics model for helminthiasis in Thailand.

At the beginning of the new millennium, helminth infections continue to be prevalent, particularly among impoverished populations. This study attempts to create the first health informatics model of helminthiasis in Thailand. The authors investigate how a health informatics model could be used to predict the control and eradication in a national control campaign. Fish-borne helminthiasis caused by Opisthorchis viverrini remains a major public health problem in many parts of South-East Asia, including Thailand, Lao PDR, Vietnam and Cambodia. The epicentre of this disease is located in north-east Thailand, where high prevalence coexists with a high incidence of cholangiocarcinoma (CHCA). The current report was conducted to determine a mathematical model of surveillance for helminthiasis while also using a geographic information system. The fish-borne helminthiasis model or the predicted equation was Y1 = 3.028 + 0.020 (elevation) - 2.098 (clay). For soil-transmitted helminthiasis, the mathematical model or the predicted equation was Y2 = -1.559 + 0.005 (rainfall) + 0.004 (elevation) - 2.198 (clay). The Ministry of Public Health has concluded that mass treatment for helminthiasis in the Thai population, targeting high-risk individuals, may be a cost-effective way to allocate limited funds. This type of approach, as well as further study on the correlation of clinical symptoms with environmental and geographic information, may offer a novel strategy to the helminth crisis.

Modeling impacts of climate change on the potential distribution of the carcinogenic liver fluke, Opisthorchis viverrini, in Thailand.

Global climate change is now regarded as imposing a significant threat of enhancing transmission of parasitic diseases. Maximum entropy species distribution modeling (MaxEnt) was used to explore how projected climate change could affect the potential distribution of the carcinogenic liver fluke, Opisthorchis viverrini, in Thailand. A range of climate variables was used: the Hadley Global Environment Model 2-Earth System (HadGEM2-ES) climate change model and also the IPCC scenarios A2a for 2050 and 2070. Occurrence data from surveys conducted in 2009 and 2014 were obtained from the Department of Disease Control, Ministry of Public Health, Thailand. The MaxEnt model performed better than random for O. viverrini with training AUC values greater than 0.8 under current and future climatic conditions. The current distribution of O. viverrini is significantly affected by precipitation and minimum temperature. According to current conditions, parts of Thailand climatically suitable for O. viverrini are mostly in the northeast and north, but the parasite is largely absent from southern Thailand. Under future climate change scenarios, the distribution of O. viverrini in 2050 should be significantly affected by precipitation, maximum temperature, and mean temperature of the wettest quarter, whereas in 2070, significant factors are likely to be precipitation during the coldest quarter, maximum, and minimum temperatures. Maps of predicted future distribution revealed a drastic decrease in presence of O. viverrini in the northeast region. The information gained from this study should be a useful reference for implementing long-term prevention and control strategies for O. viverrini in Thailand.

Comparison of the quantitative formalin ethyl acetate concentration technique and agar plate culture for diagnosis of human strongyloidiasis.

The quantitative formalin ethyl acetate concentration technique (QFEC) was compared to agar plate culture (APC) for the detection of Strongyloides stercoralis larvae. QFEC could substitute for APC only when the parasite load was higher than 50 larvae per g of stool. This study serves as a good reminder to those conducting stool exams about the sensitivity and specificity limitations of both techniques.

Detection of Opisthorchis viverrini in experimentally infected bithynid snails and cyprinoid fishes by a PCR-based method.

A PCR procedure for the detection of Opisthorchis viverrini in experimentally infected bithynid snails and cyprinoid fishes was developed. This procedure was based on primers designed from a pOV-A6 specific probe sequence giving a 330 base-pair product. The detection was accomplished in host tissue homogenates to which a single cercaria or metacercaria was introduced. PCR can detect as little as a single cercaria artificially inoculated in a snail or a single metacercaria artificially inoculated in a fish sample. The method gave a 100% positivity rate for all infected snails or fishes. The method did not yield a 330 base-pair amplified product with other digenean fluke DNAs such as Haplorchis taichui, Centrocestus spp., Echinostoma malayanum, Fasciola gigantica, animal schistosomes, Paragonimus heterotremus or Haplorchoides spp. The assay has great potential for application in epidemiological surveys of both snail and fish intermediate hosts as well as for investigation of foodborne parasites in freshwater fishes.

Affinity purified oval antigen for diagnosis of Opisthorchiasis viverrini.

Monoclonal antibodies (MAb) were raised against an oval antigen of the liver fluke Opisthorchis viverrini which is the causative agent of a parasitosis, i.e. opisthorchiasis in Thailand. The antibodies were used in an affinity column to purify the O. viverrini oval antigen from a crude extract of adult parasites by chromatography. The oval antigen was then used in a membrane (dot) ELISA for detecting antibodies in serum samples of parasitologically confirmed Opisthorchis viverrini infected individuals (adult parasites were found in stools after praziquantel treatment and salt purgation), as well as of individuals infected with other parasites and parasite-free controls. The MAb-based dot-ELISA using the affinity purified O. viverrini oval antigen revealed 100% sensitivity, specificity and accuracy for detecting O. viverrini infection. The test is simple, rapid and highly reproducible. Several samples can be tested at the same time without the requirement for special equipment or much increase in testing time; thus it is suitable for mass screening for O. viverrini exposure, especially in new endemic areas. Furthermore using serum specimens could increase patient and community compliance compared to the conventional parasitological survey which uses stool samples for the detection of O. viverrini ova, without treatment and subsequent salt purgation, this conventional method shows a low sensitivity and is also unpleasant to both the sample donors and the laboratory technicians which has historically shown a further negative impact on the final outcome.

Opisthorchiasis and intestinal fluke infections in northern Thailand.

Four hundred and thirty-one residents from 16 provinces in northern Thailand who had previously been found positive for Opisthorchis viverrini or Opisthorchis viverrini-like eggs were given praziquantel 40 mg/kg. The stool was collected for 4 to 6 times and examined for adult worms. The prevalence of Opisthorchis viverrini in this group was 11.6%. Intestinal flukes, Haplorchis taichui and Haplorchis yokogawai, were predominantly found in 63.11% and 10.44% respectively. Other intestinal flukes (Centrocestus caninus, Echinostoma malayanum, Haplorchis pumilio, Phaneropsolus bonnei, Plagiorchid flukes, Prosthodendrium molenkampi and Stellantchasmus falcatus) were also found in small numbers.

Study on the management of diarrhea in young children at community level in Thailand.

An evaluating study was carried out among 15,466 children from households randomized from 30 clusters from twelve provinces of twelve regions of Thailand. Results of this study revealed 5.13 per cent of incidence-rate of diarrhea among young children aged under five years with an average of annual prevalence of 1.3 per child. The overall mortality-rate and diarrhea associated death were 51.7 per 100,000 and 6.5 per 100,000 respectively. The utilization of ORS was 25.6 per cent while the using-rate of sugar salt solution (SSS) and the use of recommended home fluids were 2.8 and 33.8 per cent respectively. As for treatment, the intravenous therapy was 6.2 per cent and the use of different types of drugs varied from 18.0 to 21.3 per cent. Only 23.7 per cent of parents could correctly prepare the ORS. The authors have made recommendations for the strengthening of community health education aiming at better promotion of ORS and other home care practices for diarrhea as important measures for lowering mortality together with relating preventive interventions.

PIP: The impact of Thailand's diarrheal disease control program on children under 5 years of age was evaluated in a survey of 15,466 young children from 30 randomly selected clusters in 12 provinces. A total of 733 children (5.13%) had experienced a diarrhea episode in the 2 weeks preceding the survey, with an average annual diarrhea prevalence of 1.3 episodes per child. 34% of sick children were under 12 months of age. 8 children died from diarrhea (mortality rate, 51.7/100,000). 25.6% of children with diarrhea were treated with oral rehydration solution (ORS), 2.8% were given a sugar-salt solution, and 33.8% received home fluids such as rice water. 84.3% of mothers breast fed their child during the diarrhea episode and 71.3% continued other forms of feeding; however, only 8.2% increased the child's fluid intake. Observation revealed that only 23.7% of mothers were preparing the ORS correctly. 58.6% of children received antidiarrheal drugs or antibiotics. Confirmation of these findings requires a larger sample size and collection of data during both the dry and rainy seasons.

Human infection of Centrocestus caninus in Thailand.

Examination of fecal samples, collected after treatment with praziquantel, of the persons positive with opisthorchioid eggs residing in the northern provinces of Thailand, was carried out. Five adults Centrocestus were recovered in one sample from Doi Saket, Chiang Mai and one adult was found in another fecal sample from Wiang Pa Pao, Chiang Rai. The worms had 26-30 spines arranging in two rows around the oral sucker which agreed with the character of C. caninus. This is the first record of natural human infection with Centrocestus in Thailand.