RESUMEN
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.
Asunto(s)
Infecciones Asintomáticas/epidemiología , Reservorios de Enfermedades/parasitología , Malaria Falciparum/epidemiología , Malaria Vivax/epidemiología , Adolescente , Adulto , Animales , Niño , Preescolar , Estudios Transversales , Femenino , Humanos , Estadios del Ciclo de Vida , Malaria Falciparum/diagnóstico , Malaria Falciparum/parasitología , Malaria Falciparum/transmisión , Malaria Vivax/diagnóstico , Malaria Vivax/parasitología , Malaria Vivax/transmisión , Masculino , Persona de Mediana Edad , Técnicas de Diagnóstico Molecular/métodos , Mianmar/epidemiología , Plasmodium falciparum/genética , Plasmodium falciparum/aislamiento & purificación , Plasmodium vivax/genética , Plasmodium vivax/aislamiento & purificación , Prevalencia , ARN Ribosómico 18S/genética , Reacción en Cadena en Tiempo Real de la Polimerasa , Tailandia/epidemiología , Enfermedad Relacionada con los Viajes , Adulto JovenRESUMEN
BACKGROUND: Children represent a high-risk group for malaria worldwide. Among people in Thailand who have malaria during childhood, some may have multiple malaria attacks during their lifetime. Malaria may affect neurological cognition in children, resulting in short-term impairment of memory and language functions. However, little is known regarding the long-term effects of malaria infection on cognitive function. This study examines the long-term impact of malaria infection on school performance among school children living in a malaria-endemic area along the Thai-Myanmar border. METHODS: A retrospective cohort study was conducted among school children aged 6-17 years in a primary-secondary school of a sub-district of Ratchaburi Province, Thailand. History of childhood malaria infection was obtained from the medical records of the sole malaria clinic in the area. School performance was assessed by using scores for the subjects Thai Language and Mathematics in 2014. Other variables, such as demographic characteristics, perinatal history, nutritional status, and emotional intelligence, were also documented. RESULTS: A total of 457 students were included, 135 (30 %) of whom had a history of uncomplicated malaria infection. About half of the malaria-infected children had suffered infection before the age of four years. The mean scores for both Mathematics and Thai Language decreased in relation to the increasing number of malaria attacks. Most students had their last malaria episode more than two years previously. The mean scores were not associated with duration since the last malaria attack. The association between malaria infection and school performance was not significant after adjusting for potential confounders, including gender, school absenteeism over a semester term, and emotional intelligence. CONCLUSIONS: This study characterizes the long-term consequences of uncomplicated malaria disease during childhood. School performance was not associated with a history of malaria infection, considering that most students had their last malaria infection more than two years previously. These findings indicate that the impact of uncomplicated malaria infection on school performance may not be prolonged.
Asunto(s)
Enfermedades Endémicas , Discapacidades para el Aprendizaje/epidemiología , Discapacidades para el Aprendizaje/etiología , Malaria/complicaciones , Malaria/epidemiología , Instituciones Académicas , Estudiantes , Adolescente , Niño , Femenino , Humanos , Masculino , Mianmar , Estudios Retrospectivos , TailandiaRESUMEN
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.
Asunto(s)
Conocimientos, Actitudes y Práctica en Salud , Subtipo H1N1 del Virus de la Influenza A , Gripe Humana/epidemiología , Adolescente , Adulto , Anciano , Brotes de Enfermedades , Femenino , Educación en Salud/métodos , Humanos , Gripe Humana/etnología , Masculino , Persona de Mediana Edad , Mianmar/epidemiología , Población Rural , Factores Socioeconómicos , Tailandia/epidemiología , Adulto JovenRESUMEN
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.
Asunto(s)
Inundaciones , Leptospira/clasificación , Microbiología del Agua , Humanos , Leptospira/genética , Leptospirosis/epidemiología , Leptospirosis/microbiología , Filogenia , Tailandia/epidemiologíaRESUMEN
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.
Asunto(s)
Antimaláricos/administración & dosificación , Cloroquina/administración & dosificación , Terapia por Observación Directa , Malaria Vivax/tratamiento farmacológico , Primaquina/administración & dosificación , Autoadministración , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Niño , Preescolar , Femenino , Humanos , Lactante , Malaria Vivax/prevención & control , Masculino , Cumplimiento de la Medicación/estadística & datos numéricos , Persona de Mediana Edad , Mianmar , Prevención Secundaria , Tailandia , Adulto JovenRESUMEN
BACKGROUND: Plasmodium vivax has a dormant hepatic stage, called the hypnozoite, which can cause relapse months after the initial attack. For 50 years, primaquine has been used as a hypnozoitocide to radically cure P. vivax infection, but major concerns remain regarding the side-effects of the drug and adherence to the 14-day regimen. This study examined the effectiveness of using the directly-observed therapy (DOT) method for the radical treatment of P. vivax malaria infection, to prevent reappearance of the parasite within the 90-day follow-up period. Other potential risk factors for the reappearance of P. vivax were also explored. METHODS: A randomized trial was conducted from May 2007 to January 2009 in a low malaria transmission area along the Thai-Myanmar border. Patients aged ≥ 3 years diagnosed with P. vivax by microscopy, were recruited. All patients were treated with the national standard regimen of chloroquine for three days followed by primaquine for 14 days. Patients were randomized to receive DOT or self-administered therapy (SAT). All patients were followed for three months to check for any reappearance of P. vivax. RESULTS: Of the 216 patients enrolled, 109 were randomized to DOT and 107 to SAT. All patients recovered without serious adverse effects. The vivax reappearance rate was significantly lower in the DOT group than the SAT group (3.4/10,000 person-days vs. 13.5/10,000 person-days, p = 0.021). Factors related to the reappearance of vivax malaria included inadequate total primaquine dosage received (< 2.75 mg/kg), duration of fever ≤ 2 days before initiation of treatment, parasite count on admission ≥ 10,000/µl, multiple P. vivax-genotype infection, and presence of P. falciparum infection during the follow-up period. CONCLUSIONS: Adherence to the 14-day primaquine regimen is important for the radical cure of P. vivax malaria infection. Implementation of DOT reduces the reappearance rate of the parasite, and may subsequently decrease P. vivax transmission in the area.
Asunto(s)
Antimaláricos/administración & dosificación , Terapia por Observación Directa , Malaria Vivax/tratamiento farmacológico , Primaquina/administración & dosificación , Adolescente , Niño , Preescolar , Cloroquina/administración & dosificación , Femenino , Estudios de Seguimiento , Humanos , Masculino , Mianmar , Prevención Secundaria , Tailandia , Resultado del TratamientoRESUMEN
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.
Asunto(s)
Reservorios de Enfermedades/parasitología , Malaria Falciparum/epidemiología , Malaria/epidemiología , Plasmodium falciparum/aislamiento & purificación , Plasmodium vivax/aislamiento & purificación , Adolescente , Adulto , Factores de Edad , Animales , Anopheles , Antimaláricos/uso terapéutico , Niño , Estudios de Cohortes , Femenino , Humanos , Incidencia , Insectos Vectores , Malaria/diagnóstico , Malaria/tratamiento farmacológico , Malaria/transmisión , Malaria Falciparum/diagnóstico , Malaria Falciparum/tratamiento farmacológico , Malaria Falciparum/transmisión , Masculino , Persona de Mediana Edad , Mianmar/epidemiología , Vigilancia de la Población , Características de la Residencia , Estudios Retrospectivos , Factores de Riesgo , Estaciones del Año , Factores Sexuales , Adulto JovenRESUMEN
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.
Asunto(s)
Antimaláricos/farmacología , Malaria Falciparum/transmisión , Plasmodium falciparum/efectos de los fármacos , Primaquina/farmacología , Animales , Antimaláricos/uso terapéutico , Pueblo Asiatico , Enfermedades Endémicas , Humanos , Malaria Falciparum/tratamiento farmacológico , Malaria Falciparum/epidemiología , Malaria Falciparum/parasitología , Modelos Biológicos , Mianmar/epidemiología , Parasitemia/tratamiento farmacológico , Parasitemia/epidemiología , Vigilancia de la Población , Primaquina/uso terapéutico , Factores de Tiempo , Resultado del TratamientoRESUMEN
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.