Spatiotemporal epidemiology, environmental correlates, and demography of malaria in Tak Province, Thailand (2012-2015).

BACKGROUND: Tak Province, at the Thai-Myanmar border, is one of three high malaria incidence areas in Thailand. This study aimed to describe and identify possible factors driving the spatiotemporal trends of disease incidence from 2012 to 2015. METHODS: Climate variables and forest cover were correlated with malaria incidence using Pearson's r. Statistically significant clusters of high (hot spots) and low (cold spots) annual parasite incidence per 1000 population (API) were identified using Getis-Ord Gi* statistic. RESULTS: The total number of confirmed cases declined by 76% from 2012 to 2015 (Plasmodium falciparum by 81%, Plasmodium vivax by 73%). Incidence was highly seasonal with two main annual peaks. Most cases were male (62.75%), ≥ 15 years (56.07%), and of Myanmar (56.64%) or Thai (39.25%) nationality. Median temperature (1- and 2-month lags), average temperature (1- and 2-month lags) and average relative humidity (2- and 3-month lags) correlated positively with monthly total, P. falciparum and P. vivax API. Total rainfall in the same month correlated with API for total cases and P. vivax but not P. falciparum. At sub-district level, percentage forest cover had a low positive correlation with P. falciparum, P. vivax, and total API in most years. There was a decrease in API in most sub-districts for both P. falciparum and P. vivax. Sub-districts with the highest API were in the Tha Song Yang and Umphang Districts along the Thai-Myanmar border. Annual hot spots were mostly in the extreme north and south of the province. CONCLUSIONS: There has been a large decline in reported clinical malaria from 2012 to 2015 in Tak Province. API was correlated with monthly climate and annual forest cover but these did not account for the trends over time. Ongoing elimination interventions on one or both sides of the border are more likely to have been the cause but it was not possible to assess this due to a lack of suitable data. Two main hot spot areas were identified that could be targeted for intensified elimination activities.

Prevalence and Alternative Treatment of Head-Lice Infestation in Rural Thailand: A Community-Based Study.

Head-lice infestation, pediculosis capitis, remains a public-health burden in many countries. The widely used first-line pediculicides and alternative treatments are often too costly for use in poor socio-economic settings. Ivermectin has been considered an alternate treatment for field practice. This study was composed of 2 parts, a cross-sectional survey and an intervention study. The main objectives were to determine the prevalence and potential factors associated with head-lice infestation, and to evaluate the effectiveness and safety of oral ivermectin administration. A community-based cross-sectional survey was conducted among 890 villagers in rural areas along Thai-Myanmar border. Females with infestations were eligible for the intervention study, and 181 participated in the intervention study. A post-treatment survey was conducted to assess acceptance of ivermectin as a treatment choice. Data analysis used descriptive statistics and a generalized-estimation-equation model adjusted for cluster effect. The study revealed the prevalence of head-lice infestation was 50% among females and only 3% among males. Age stratification showed a high prevalence among females aged <20 years, and among 50% of female school-children. The prevalence was persistent among those with a history of infestation. The major risk factors were residing in a setting with other infected cases, and sharing a hair comb. The study also confirmed that ivermectin was safe and effective for field-based practice. It was considered a preferable treatment option. In conclusion, behavior-change communication should be implemented to reduce the observed high prevalence of headlice infestation. Ivermectin may be an alternative choice for head-lice treatment, especially in remote areas.

Knowledge, attitudes and practices (kap) regarding influenza A (H1N1) among a population living along Thai-Myanmar border, Ratchaburi Province, Thailand.

The 2009 influenza A (H1N1) outbreaks in Thailand was successfully controlled, partly through the use of electronic media to educate the public. People living along the Thai-Myanmar border may have less access to this electronic media or might have health beliefs that differ from the general Thai population with potential to impact an influenza outbreak. We conducted a survey to assess the knowledge, attitudes and practices regarding influenza among people living along the Thai-Myanmar boder in Ratchaburi Province, Thailand. Of 110 house- holds surveyed, 96% were Karen ethnicity. Greater than 50% were uneducated and most had a low family income. Knowledge about influenza was low. Attitudes regarding infection were mostly negative among the elderly in this area. Practices regarding influenza were moderately good. Education level was associated with knowledge and practice. Income level and wealth indicators were associated with knowledge and having a radio or TV was associated with good practices. Preventive behavior was associated with good knowledge but not with attitudes about influenza. Health education campaigns are needed in these communities to help people adopt desired changes in behavior to improve personal hygiene.

Love or conflict: A qualitative study of the human-long tailed macaque interface in Nakhon Sawan Province, Thailand.

A wide range of zoonotic pathogens can be transmitted during human-wildlife interactions. Few qualitative studies have been conducted on human-nonhuman primate interfaces in Thailand, notably direct and indirect contact. Since Long-tailed macaques (LTMs) are prevalent in Thailand's Banphot Phisai district, part of Nakhon Sawan province, this qualitative study was conducted in 2019 to determine in-depth contact characteristics between humans and LTMs in the communities. Key informant interviews (KIIs) and focus group discussions (FGDs) were conducted with 35 villagers who reported close contact with LTMs in this study location. The results showed that villagers had different levels of contact with LTMs, depending on their occupations, perceptions, beliefs, religions, previous experiences, and local regulations. Monks in temples and vendors selling food for LTMs were reported to have the closest contact with them. LTMs have been reported to destroy personal property, houses, buildings, and crops. However, the villagers do not hurt them due to their religious beliefs relating to a respected abbot (a man who headed an abbey of monks). Even community members have had extensive interaction with LTMs, but they lacked awareness and information regarding diseases transmitted to humans directly or indirectly by non-human primates. Therefore, individuals who have frequent and close contact with LTMs should be provided health education, and appropriate behavioral change communication interventions should be performed. Furthermore, the results could be used to develop future disease prevention strategies and public awareness campaigns in the area.

Rodent-Human Interface: Behavioral Risk Factors and Leptospirosis in a Province in the Central Region of Thailand.

This sequential explanatory mixed-method study consisted of analytical, cross-sectional, and qualitative studies. The research was conducted in the Khao Nor and Khao Kaew areas of the Banphot Pisai districts of Nakhon Sawan Province in 2019. Here, we examined the rodent contact characteristics of villagers in these areas and determined the potential characteristics/risk factors associated with rodents using a semi-structured questionnaire, key informant interview (KII), and focus group discussion (FGD). Results of the quantitative study (N1 = 372) characterized participants that contacted rodents per gender, age, occupation, knowledge, attitude, and practice (KAP), including their cultural contexts, and beliefs. Ninety participants (24.2%) reported contact with rodents, and the reasons for their direct physical rodent contact were hunting (35, 9.4%), killing (41, 11.0%), preparing rodents as food (33, 8.9%), consuming cooked meats (12, 3.2%), feeding food (4, 1.1%), cleaning feces (17, 4.6%), and cleaning carcasses (33, 8.9%). Moreover, logistic regression results showed that males encountering rodents were statistically significant (Adjusted OR = 3.137, 95% CI 1.914-5.139, p < 0.001). Low monthly household income (

Directly observed therapy with primaquine to reduce the recurrence rate of plasmodium vivax infection along the Thai-Myanmar border.

This study was carried out from April 2005 to June 2006 to evaluate the recurrence of P. vivax malaria infection in relation to drug compliance along the Thai-Myanmar border in Ratchaburi, Thailand. Ninety-two patients with vivax malaria were sequentially assigned to 2 groups. Both groups received a standard dose of chloroquine (total dose = 2.5 g) for 3 days and primaquine (total dose = 210 mg) for 14 days. The experimental group received a full course of treatment using daily directly observed therapy (DOT) while subjects in the control group were given the medication with necessary instructions to take as self-administered therapy (SAT). Patients were followed up for 3 months on Days 14, 21, 28, 60 and 90. Five of 46 patients from the SAT group had recurrence of malaria on Days 21, 44, 60, 72 and 87. Recurrence was not observed among patients in the DOT group. Survival analysis also showed significant differences between the SAT and DOT groups (p <0.05). The study suggests patient compliance with the 14-day primaquine treatment with DOT improve the outcome of .vivax malaria treatment.

The impact of human reservoir of malaria at a community-level on individual malaria occurrence in a low malaria transmission setting along the Thai-Myanmar border.

BACKGROUND: The probability of contracting malaria in a given individual is determined not only by the individual's characteristics, but also the ecological factors that characterize the level of human-vector contact in the population. Examination of the relationship between "individual" and "supra-individual" variables over time is important for understanding the local malaria epidemiology. This is essential for planning effective intervention strategies specifically for each location. METHODS: A retrospective cohort study was conducted, which followed a community-cohort of about 3,500 residents in seven hamlets along the Thai-Myanmar border between 1999 and 2006. Potential malaria determinants measured at different levels (temporal variables, individual variables, and hamlet variables) were incorporated into multilevel models to estimate their effects on an individual's risk of malaria attack. RESULTS: The monthly minimum temperature was significantly associated with the seasonal variation of malaria risk. An individual risk of malaria attack decreased by about 50% during the period that active surveillance was conducted; an additional 15% and 25% reduction of Plasmodium falciparum and Plasmodium vivax incidence, respectively, was observed after the use of artesunate-mefloquine combination therapy (ACT) for treatment of P. falciparum. Male children (age < 16 years old) were at highest risk of both P. falciparum and P. vivax attack. An increase in the hamlet's incidence of P. falciparum and P. vivax by 1 per 100 persons in a previous month resulted in 1.14 and 1.34 times increase in the risk of P. falciparum and P. vivax, respectively, among individuals in a particular hamlet. CONCLUSION: In a small area with low malaria transmission intensity, the variation in mosquito abundance is relatively similar across the residential areas; incidence of malaria between hamlets, which reflects the community level of human infectious reservoirs, is an important predictor for the malaria risk among individuals within these hamlets. Therefore, local malaria control strategies should focus on interventions that aim to reduce the gametocyte carriage in the population, such as early detection and treatment programmes and the use of ACT for P. falciparum.

Optimally timing primaquine treatment to reduce Plasmodium falciparum transmission in low endemicity Thai-Myanmar border populations.

BACKGROUND: Effective malaria control has successfully reduced the malaria burden in many countries, but to eliminate malaria, these countries will need to further improve their control efforts. Here, a malaria control programme was critically evaluated in a very low-endemicity Thai-Myanmar border population, where early detection and prompt treatment have substantially reduced, though not ended, Plasmodium falciparum transmission, in part due to carriage of late-maturing gametocytes that remain post-treatment. To counter this effect, the WHO recommends the use of a single oral dose of primaquine along with an effective blood schizonticide. However, while the effectiveness of primaquine as a gametocidal agent is widely documented, the mismatch between primaquine's short half-life, the long-delay for gametocyte maturation and the proper timing of primaquine administration have not been studied. METHODS: Mathematical models were constructed to simulate 8-year surveillance data, between 1999 and 2006, of seven villages along the Thai-Myanmar border. A simple model was developed to consider primaquine pharmacokinetics and pharmacodynamics, gametocyte carriage, and infectivity. RESULTS: In these populations, transmission intensity is very low, so the P. falciparum parasite rate is strongly linked to imported malaria and to the fraction of cases not treated. Given a 3.6-day half-life of gametocyte, the estimated duration of infectiousness would be reduced by 10 days for every 10-fold reduction in initial gametocyte densities. Infectiousness from mature gametocytes would last two to four weeks and sustain some transmission, depending on the initial parasite densities, but the residual mature gametocytes could be eliminated by primaquine. Because of the short half-life of primaquine (approximately eight hours), it was immediately obvious that with early administration (within three days after an acute attack), primaquine would not be present when mature gametocytes emerged eight days after the appearance of asexual blood-stage parasites. A model of optimal timing suggests that primaquine follow-up approximately eight days after a clinical episode could further reduce the duration of infectiousness from two to four weeks down to a few days. The prospects of malaria elimination would be substantially improved by changing the timing of primaquine administration and combining this with effective detection and management of imported malaria cases. The value of using primaquine to reduce residual gametocyte densities and to reduce malaria transmission was considered in the context of a malaria transmission model; the added benefit of the primaquine follow-up treatment would be relatively large only if a high fraction of patients (>95%) are initially treated with schizonticidal agents. CONCLUSION: Mathematical models have previously identified the long duration of P. falciparum asexual blood-stage infections as a critical point in maintaining malaria transmission, but infectiousness can persist for two to four weeks because of residual populations of mature gametocytes. Simulations from new models suggest that, in areas where a large fraction of malaria cases are treated, curing the asexual parasitaemia in a primary infection, and curing mature gametocyte infections with an eight-day follow-up treatment with primaquine have approximately the same proportional effects on reducing the infectious period. Changing the timing of primaquine administration would, in all likelihood, interrupt transmission in this area with very good health systems and with very low endemicity.

Longitudinal study of Plasmodium falciparum and Plasmodium vivax in a Karen population in Thailand.

BACKGROUND: Clinical case treatment of malaria infections where Plasmodium falciparum and Plasmodium vivax are sympatric has achieved effective reductions in P. falciparum prevalence and incidence rates, but has been less successful for P. vivax. The high transmissibility of P. vivax and its capacity to relapse have been suggested to make it a harder parasite species to control. METHODS: A clinical malaria case treatment programme was carried out over a decade in a Karen community composed of seven hamlets on the Thai-Myanmar border. RESULTS: From 1994 to 2004, prevalence rates of both P. falciparum and P. vivax decreased by 70-90% in six of the seven study hamlets, but were unchanged in one hamlet. Overall, incidence rates decreased by 72% and 76% for P. falciparum and P. vivax respectively over the period 1999-2004. The age-incidence and prevalence curves suggested that P. vivax was more transmissible than P. falciparum despite a greater overall burden of infection with P. falciparum. Male gender was associated with increased risk of clinical presentation with either parasite species. Children (< 15 years old) had an increased risk of presenting with P. vivax but not P. falciparum. CONCLUSION: There was a considerable reduction in incidence rates of both P. vivax and P. falciparum over a decade following implementation of a case treatment programme. The concern that intervention methods would inadvertently favour one species over another, or even lead to an increase in one parasite species, does not appear to be fulfilled in this case.

Very high carriage of gametocytes in asymptomatic low-density Plasmodium falciparum and P. vivax infections in western Thailand.

BACKGROUND: Low-density asymptomatic infections of Plasmodium spp. are common in low endemicity areas worldwide, but outside Africa, their contribution to malaria transmission is poorly understood. Community-based studies with highly sensitive molecular diagnostics are needed to quantify the asymptomatic reservoir of Plasmodium falciparum and P. vivax infections in Thai communities. METHODS: A cross-sectional survey of 4309 participants was conducted in three endemic areas in Kanchanaburi and Ratchaburi provinces of Thailand in 2012. The presence of P. falciparum and P. vivax parasites was determined using 18S rRNA qPCR. Gametocytes were also detected by pfs25 / pvs25 qRT-PCRs. RESULTS: A total of 133 individuals were found infected with P. vivax (3.09%), 37 with P. falciparum (0.86%), and 11 with mixed P. vivax/ P. falciparum (0.26%). The clear majority of both P. vivax (91.7%) and P. falciparum (89.8%) infections were not accompanied by any febrile symptoms. Infections with either species were most common in adolescent and adult males. Recent travel to Myanmar was highly associated with P. falciparum (OR = 9.0, P = 0.001) but not P. vivax infections (P = 0.13). A large number of P. vivax (71.5%) and P. falciparum (72.0%) infections were gametocyte positive by pvs25/pfs25 qRT-PCR. Detection of gametocyte-specific pvs25 and pfs25 transcripts was strongly dependent on parasite density. pvs25 transcript numbers, a measure of gametocyte density, were also highly correlated with parasite density (r 2 = 0.82, P < 0.001). CONCLUSIONS: Asymptomatic infections with Plasmodium spp. were common in western Thai communities in 2012. The high prevalence of gametocytes indicates that these infections may contribute substantially to the maintenance of local malaria transmission.

Early detection of malaria in an endemic area: model development.

A malaria epidemic warning system was established in Thailand in 1984 using graphs displaying the median or mean incidence of malaria over the previous five years compiled from malaria surveillance data throughout the country. This reporting mechanism is not timely enough to detect the occurrence of a malaria epidemic which usually occurs at the district level over a short period of time. An alternative method for early detection of a malaria epidemic employing the Poisson model has been proposed. The development of this early malaria epidemic detection model involved 3 steps: model specification, model validation and model testing. The model was based on data collected at the Vector Borne Disease Control Unit (VBDU) Level. The results of model testing reveal the model can detect increasing numbers of cases earlier, one to two weeks prior to reaching their highest peak of transmission. The system was tested using data from Kanchanaburi Province during 2000 to 2001. Results from model testing show the model may be used for monitoring the weekly malaria situation at the district level. The Poisson model was able to detect malaria early in a highly endemic province with a satisfactory level of prediction. As the application is essential for the malaria officers in monitoring of malaria epidemics, this early detection system was introduced into malaria epidemiological work. The model may be helpful in the decision making process, planning and budget allocation for the Malaria Control Program. The software for early malaria detection is currently implemented in several endemic areas throughout Thailand.

Chronicle of malaria epidemics in Thailand, 1980-2000.

The occurrence of malaria epidemics in Thailand was reviewed from the malaria surveillance report of the National Malaria Control Program. The literature review revealed that the four epidemic periods recorded during 1980-2000 almost always occurred in the provinces and districts located along international borders. Malaria epidemics are caused by various factors such as: extensive population movement, multi-drug resistance development, low immune status of the population, lack of knowledge and appropriate personal protection against mosquito biting, and the re-emergence of malaria transmission in low malarious areas. Such factors can lead to changes in the parasite ratio and appearance of malaria epidemics throughout the country. Evidence related to the burden of malaria epidemics was also reviewed to identify causal factors that will be helpful in future research.

Trend of malaria incidence in highly endemic provinces along the Thai borders, 1991-2001.

The intercountry border areas of Thailand have high malaria receptivity and vulnerability that present numerous problems in the control of malaria transmission. This study focused on the 30 provinces of Thailand situated next to neighboring countries, which can be divided into 4 groups: the Thai-Myanmar border (10 provinces), the Thai-Cambodia border (6 provinces), the Thai-Lao border (10 provinces) and the Thai-Malaysia border (4 provinces). The purpose of the present study was to describe the pattern and trend of malaria incidence in the highly endemic provinces along the Thai borders for the 11 years from 1991 to 2001. Analysis of trends showed the distribution of malaria parasites to have shifted from a preponderance of Plasmodium falciparum to Plasmodium vivax along the western border with Myanmar, the northern border with Lao PDR and along the eastern border with Cambodia whereas the southern border with Malaysia the pattern changed from a preponderance of P. vivax to P. falciparum, since 1997. There was a significant difference in annual parasite incidence between borders and non-border districts, especially along the Thai-Myanmar and Thai-Cambodia borders. It is thus evident that all border districts should pay more attention to control of malaria transmission and the activities of the malaria surveillance system, and that monitoring and evaluation of the Thai Malaria Control Program needs to be performed consistently, including some areas where a few malaria cases were found as well as in malaria free areas.

Mekong malaria. II. Update of malaria, multi-drug resistance and economic development in the Mekong region of Southeast Asia.

In an expansion of the first Mekong Malaria monograph published in 1999, this second monograph updates the malaria database in the countries comprising the Mekong region of Southeast Asia. The update adds another 3 years' information to cover cumulative data from the 6 Mekong countries (Cambodia, China/Yunnan, Lao PDR, Myanmar, Thailand, Viet Nam) for the six-year period 1999-2001. The objective is to generate a more comprehensive regional perspective in what is a global epicenter of drug resistant falciparum malaria, in order to improve malaria control on a regional basis in the context of social and economic change. The further application of geographical information systems (GIS) to the analysis has underscored the overall asymmetry of disease patterns in the region, with increased emphasis on population mobility in disease spread. Of great importance is the continuing expansion of resistance of P. falciparum to antimalarial drugs in common use and the increasing employment of differing drug combinations as a result. The variation in drug policy among the 6 countries still represents a major obstacle to the institution of region-wide restrictions on drug misuse. An important step forward has been the establishment of 36 sentinel sites throughout the 6 countries, with the objective of standardizing the drug monitoring process; while not all sentinel sites are fully operational yet, the initial implementation has already given encouraging results in relation to disease monitoring. Some decreases in malaria mortality have been recorded. The disease patterns delineated by GIS are particularly instructive when focused on inter-country distribution, which is where more local collaborative effort can be made to rationalize resource utilization and policy development. Placing disease data in the context of socio-economic trends within and between countries serves to further identify the needs and the potential for placing emphasis on resource rationalization on a regional basis. Despite the difficulties, the 6-year time frame represented in this monograph gives confidence that the now well established collaboration is becoming a major factor in improving malaria control on a regional basis and hopefully redressing to a substantial degree the key problem of spread of drug resistance regionally and eventually globally.

Advantages of using voiced questionnaire and image capture application for data collection from a minority group in rural areas along the Thailand-Myanmar border.

AIMS: To compare the quality of data collection via electronic data capture (EDC) with voiced questionnaire (QNN) and data image capture features using a tablet versus standard paper-based QNN, to assess the user's perception of using the EDC tool, and to compare user satisfaction with the two methods. STUDY DESIGN: Randomised cross-over study. Study sites: This study was conducted in two villages along the Thailand-Myanmar border. METHODOLOGY: This study included 30 community health volunteers (CHVs) and 120 Karen hill tribe villagers. Employing a cross-over study design, the CHVs were allocated randomly to two groups, in which they performed interviews in different sequences using EDC and QNN. RESULTS: Data discrepancies were found between the two data-collection methods, when data from the paper-based and image-capture methods were compared, and when conducting skip pattern questions. More than 90% of the CHVs perceived the EDC to be useful and easy to use. Both interviewers and interviewees were more satisfied with the EDC compared with QNN in terms of format, ease of use, and system speed. CONCLUSION: The EDC can effectively be used as an alternative method to paper-based QNNs for data collection. It produces more accurate data that can be considered evidence-based.

Leptospira species in floodwater during the 2011 floods in the Bangkok Metropolitan Region, Thailand.

Floodwater samples (N = 110) collected during the 2011 Bangkok floods were tested for Leptospira using culture and polymerase chain reaction (PCR); 65 samples were PCR-positive for putatively non-pathogenic Leptospira species, 1 sample contained a putatively pathogenic Leptospira, and 6 samples contained Leptospira clustering phylogenetically with the intermediate group. The low prevalence of pathogenic and intermediate Leptospira in floodwater was consistent with the low number of human leptospirosis cases reported to the Bureau of Epidemiology in Thailand. This study provides baseline information on environmental Leptospira in Bangkok together with a set of laboratory tests that could be readily deployed in the event of future flooding.