Evaluation of mass drug administration in the program to control imported lymphatic filariasis in Thailand.

BACKGROUND: Migration plays a major role in the emergence and resurgence of lymphatic filariasis (LF) in many countries. Because of the high prevalence of Imported Bancroftian Filariasis (IBF) caused by nocturnally periodic Wuchereria bancrofti and the intensive movement of immigrant workers from endemic areas, Thailand has implemented two doses of 6 mg/kg diethylcarbamazine (DEC) with interval of 6 months to prevent IBF. In areas where immigrants are very mobile, the administration of DEC may be compromised. This study aimed to evaluate DEC administration and its barriers in such areas. METHODS: A cross-sectional study with two-stage stratified cluster sampling was conducted. We selected Myanmar immigrants aged >18 years from factory and fishery areas of Samut Sakhon Province for interview with a structured questionnaire. We also interviewed health personnel regarding the functions of the LF program and practice of DEC delivery among immigrants. Associations were measured by multiple logistic regression, at P <0.05. RESULTS: DEC coverage among the immigrants was 75 %, below the national target. All had received DEC only once during health examinations at general hospitals for work permit renewals. None of the health centers in each community provided DEC. Significant barriers to DEC access included being undocumented (adjusted OR = 74.23; 95 % CI = 26.32-209.34), unemployed (adjusted OR = 5.09; 95 % CI = 3.39-7.64), daily employed (adjusted OR = 4.33; 95 % CI = 2.91-6.46), short-term immigrant (adjusted OR = 1.62; 95 % CI = 1.04-2.52) and living in a fishery area (adjusted OR = 1.57; 95 % CI = 1.04-2.52). Incorrect perceptions about the side-effects of DEC also obstructed DEC access for Myanmar immigrants. All positive LF antigenic immigrants reported visiting and emigrating from LF-endemic areas. CONCLUSION: Hospital-based DEC administration was an inappropriate approach to DEC delivery in areas with highly mobile Myanmar immigrants. Incorporating health-center personnel in DEC delivery twice yearly and improving the perceptions of DEC side effects would likely increase DEC coverage among Myanmar immigrants.

Protective efficacy of the recombinant, live-attenuated, CYD tetravalent dengue vaccine in Thai schoolchildren: a randomised, controlled phase 2b trial.

BACKGROUND: Roughly half the world's population live in dengue-endemic countries, but no vaccine is licensed. We investigated the efficacy of a recombinant, live, attenuated tetravalent dengue vaccine. METHODS: In this observer-masked, randomised, controlled, monocentre, phase 2b, proof-of-concept trial, healthy Thai schoolchildren aged 4-11 years were randomly assigned (2:1) to receive three injections of dengue vaccine or control (rabies vaccine or placebo) at months 0, 6, and 12. Randomisation was by computer-generated permuted blocks of six and participants were assigned with an interactive response system. Participants were actively followed up until month 25. All acute febrile illnesses were investigated. Dengue viraemia was confirmed by serotype-specific RT-PCR and non-structural protein 1 ELISA. The primary objective was to assess protective efficacy against virologically confirmed, symptomatic dengue, irrespective of severity or serotype, occurring 1 month or longer after the third injection (per-protocol analysis). This trial is registered at ClinicalTrials.gov, NCT00842530. FINDINGS: 4002 participants were assigned to vaccine (n=2669) or control (n=1333). 3673 were included in the primary analysis (2452 vaccine, 1221 control). 134 cases of virologically confirmed dengue occurred during the study. Efficacy was 30·2% (95% CI -13·4 to 56·6), and differed by serotype. Dengue vaccine was well tolerated, with no safety signals after 2 years of follow-up after the first dose. INTERPRETATION: These data show for the first time that a safe vaccine against dengue is possible. Ongoing large-scale phase 3 studies in various epidemiological settings will provide pivotal data for the CYD dengue vaccine candidate. FUNDING: Sanofi Pasteur.

Dengue infection in children in Ratchaburi, Thailand: a cohort study. I. Epidemiology of symptomatic acute dengue infection in children, 2006-2009.

BACKGROUND: There is an urgent need to field test dengue vaccines to determine their role in the control of the disease. Our aims were to study dengue epidemiology and prepare the site for a dengue vaccine efficacy trial. METHODS AND FINDINGS: We performed a prospective cohort study of children in primary schools in central Thailand from 2006 through 2009. We assessed the epidemiology of dengue by active fever surveillance for acute febrile illness as detected by school absenteeism and telephone contact of parents, and dengue diagnostic testing. Dengue accounted for 394 (6.74%) of the 5,842 febrile cases identified in 2882, 3104, 2717 and 2312 student person-years over the four years, respectively. Dengue incidence was 1.77% in 2006, 3.58% in 2007, 5.74% in 2008 and 3.29% in 2009. Mean dengue incidence over the 4 years was 3.6%. Dengue virus (DENV) types were determined in 333 (84.5%) of positive specimens; DENV serotype 1 (DENV-1) was the most common (43%), followed by DENV-2 (29%), DENV-3 (20%) and DENV-4 (8%). Disease severity ranged from dengue hemorrhagic fever (DHF) in 42 (10.5%) cases, dengue fever (DF) in 142 (35.5%) cases and undifferentiated fever (UF) in 210 (52.5%) cases. All four DENV serotypes were involved in all disease severity. A majority of cases had secondary DENV infection, 95% in DHF, 88.7% in DF and 81.9% in UF. Two DHF (0.5%) cases had primary DENV-3 infection. CONCLUSION: The results illustrate the high incidence of dengue with all four DENV serotypes in primary school children, with approximately 50% of disease manifesting as mild clinical symptoms of UF, not meeting the 1997 WHO criteria for dengue. Severe disease (DHF) occurred in one tenth of cases. Data of this type are required for clinical trials to evaluate the efficacy of dengue vaccines in large scale clinical trials.

Dengue infection in children in Ratchaburi, Thailand: a cohort study. II. Clinical manifestations.

BACKGROUND: Dengue infection is one of the most important mosquito-borne diseases. More data regarding the disease burden and the prevalence of each clinical spectrum among symptomatic infections and the clinical manifestations are needed. This study aims to describe the incidence and clinical manifestations of symptomatic dengue infection in Thai children during 2006 through 2008. STUDY DESIGN: This study is a school-based prospective open cohort study with a 9,448 person-year follow-up in children aged 3-14 years. Active surveillance for febrile illnesses was done in the studied subjects. Subjects who had febrile illness were asked to visit the study hospital for clinical and laboratory evaluation, treatment, and serological tests for dengue infection. The clinical data from medical records, diary cards, and data collection forms were collected and analyzed. RESULTS: Dengue infections were the causes of 12.1% of febrile illnesses attending the hospital, including undifferentiated fever (UF) (49.8%), dengue fever (DF) (39.3%) and dengue hemorrhagic fever (DHF) (10.9%). Headache, anorexia, nausea/vomiting and myalgia were common symptoms occurring in more than half of the patients. The more severe dengue spectrum (i.e., DHF) had higher temperature, higher prevalence of nausea/vomiting, abdominal pain, rash, diarrhea, petechiae, hepatomegaly and lower platelet count. DHF cases also had significantly higher prevalence of anorexia, nausea/vomiting and abdominal pain during day 3-6 and diarrhea during day 4-6 of illness. The absence of nausea/vomiting, abdominal pain, diarrhea, petechiae, hepatomegaly and positive tourniquet test may predict non-DHF. CONCLUSION: Among symptomatic dengue infection, UF is most common followed by DF and DHF. Some clinical manifestations may be useful to predict the more severe disease (i.e., DHF). This study presents additional information in the clinical spectra of symptomatic dengue infection.

Detection of filarial parasites in domestic cats by PCR-RFLP of ITS1.

Lymphatic filariasis has been targeted by the World Health Organization (WHO) to be eliminated by the year 2020. In addition to chemotherapy and vector control, the control of reservoir hosts is necessary for the control program to succeed. Malayan filariasis, caused by Brugia malayi, is endemic in the South of Thailand where domestic cats serve as the major reservoir host. However, in nature, domestic cats also carry B. pahangi, Dirofilaria immitis and D. repens infections and it is difficult to distinguish the different filarial species from each other just by morphology. To assess the burden of filarial parasites, we performed a study on domestic cats in an endemic area of malayan filariasis in the Prasang district, of Surat Thani, a province in Southern Thailand. Together with Giemsa staining and acid phosphatase activity studies, we performed PCR-RFLP analysis on the first internal transcribed spacer (ITS1) region of ribosomal DNA (rDNA). PCR-RFLP with Ase I could clearly differentiate between B. malayi, B. pahangi, D. immitis and D. repens. Out of the 52 cats studied, filarial parasites were identified in 5 (9.5%) cats, of which 4 (7.6%) were B. pahangi and 1 (1.9%) D. immitis. This PCR-RFLP technique detected two additional cats that were not detected by microscopy. The domestic cats are not an important host of B. malayi in this region. We could develop the PCR-RFLP assay test for differentiating filarial nematodes which can be applied to survey human, animal reservoir hosts and mosquito vectors in endemic areas.

Bottle and biochemical assays on temephos resistance in Aedes aegypti in Thailand.

The bottle bioassay measuring the time-mortality rate is a simplified procedure for detecting insecticide resistance. It can be used with a biochemical microplate assay to identify the mechanism involved. This integrated approach was used to detect temephos resistance in Aedes aegypti from Nonthaburi (lowest use) and Roi Et (highest use). Ae. aegypti BKK1 laboratory strain was used as the susceptible reference strain. The appropriate concentration of insecticide for bottle bioassay was determined empirically for Ae. aegypti BKK1 strain and found to be in the range of 800-1,050 microg/bottle. The time-mortality rate at 800 microg/bottle was 170 +/- 8.66 minutes, significantly different from the time-mortality rates in the 850, 900, 950, and 1,050 microg/bottle (p = 0.008) concentrations, which were 135 +/- 15.00, 140 +/- 8.66, 135 +/- 15.00, and 125 +/- 8.66 minutes, respectively. The cut-off concentration selected for resistance detection was 850 microg/bottle. The time-mortality rate for the Roi Et strain was 382 +/- 26.41 minutes, significantly higher than the Nonthaburi (150 +/- 25.10 minutes) and BKK1 strains (145 +/- 20.49 minutes) (p < 0.001). The temephos resistance ratio (RR100) for the Ae. aegypti Roi Et strain was 2.64-fold higher at lethal time (LT100) than for the reference Ae. aegypti BKK1 strain. The mean optical density (OD) value from the biochemical microplate assay for the non-specific esterase of the Roi Et strain was higher than the mean OD for the non-specific esterase of both the Nonthaburi and BKK1 strains. Insensitive acetylcholinesterase was not found to be responsible for the resistance in the field-collected mosquitos. This study suggests that esterase detoxification is the primary cause of resistance in the Ae. aegypti population from Roi Et. Both the bottle bioassay and the biochemical microplate assay were proven to be promising tools for initial detection and field surveillance for temephos resistance.

The geographic information system as an epidemiological tool in the surveillance of dengue virus-infected Aedes mosquitos.

A Geographic Information System (GIS) was used as analysis tool to study the spatial distribution of dengue virus-infected Aedes mosquitos in Thailand. Global Positioning System (GPS) instruments were used to map villages involved in dengue epidemiological studies in Ratchaburi Province, Thailand. Differentially processed GPS data, with a spatial resolution of approximately 1 meter, were incorporated into a GIS for analysis and mapping. Databases associated with a village GIS included village number, Aedes aegypti populations, and test results. Epidemiological surveillance for dengue infection through the detection of the dengue virus type(s) infecting Aedes mosquitos during epidemic periods constitutes a reliable sentinel system for dengue outbreaks. Various techniques were applied including: enzyme linked immunosorbent assay (ELISA), indirect immunofluorescent assay (IFA), and reverse transcriptase-polymerase chain reaction (RT-PCR) assay for the virologic surveillance of the type-specific detection of dengue viruses in artificially infected and in field-caught adult Aedes mosquitos. In laboratory experiments, all assays showed sufficient sensitively to detect one virus infected mosquito and the rapid RT-PCR clearly showed serotype-specificity with very high detection sensitivity. In the field study conducted from April to September 2000, female adult Aedes mosquitos were collected from selected dengue-sensitive areas in Chom Bung district, Ratchaburi Province and assayed by ELISA, IFA and RT-PCR with 18.3% (44/240), 28.98% (20/69) and 15% (3/20) positive for dengue virus, respectively. Geographic distribution of the virus-infected Aedes mosquitos and household locations were demonstrated by the GPS and the GIS. The development of disease mapping data coupled with RT-PCR laboratory-based surveillance of dengue virus infection can successfully serve as epidemiologic tools in an early warning system for dengue hemorrhagic fever (DHF) epidemics.

Relationship between male hydrocele and infection prevalences in clustered communities with uncertain transmission of Wuchereria bancrofti on the Thailand-Myanmar border.

A cross-sectional community-based study was conducted in three clustered communities, belonging to a single small village in Mae Chan subdistrict, Umphang district, Tak Province, close to the Thailand-Myanmar border, where regular night blood survey have been discontinued since 1997 and no epidemiological study had been conducted. In order to understand prevalences of distribution of male hydrocele and infection in clinically diagnostic and epidemiologic implications in uncertain transmission of Wuchereria bancrofti, we analyzed the relationship between male hydrocele and community infection prevalences in 219 (90.5% coverage) subjects aged > or =1 year old, including 54.8% migratory and 45.2% local Karen inhabitants. Migratory inhabitants tended to have high prevalence of antigenemia (p < 0.05) and hydrocele. Overall rates of 23.7% antigenemia, 3.7% microfilaremia, and 4.6% male hydrocele were observed. Male hydrocele prevalence was significantly correlated (r = 0.348, p < 0.0001) with antigenemia prevalence, but not with microfilaremia prevalence (r = 0.065, p = 0.493). However, high antigenemia prevalence in local inhabitants was evident, particularly antigenemia prevalence in children suggesting that transmission in the village may have occurred in recent years.