Serostudies are needed to answer generalizable questions on disease risk. However, recruitment is usually biased by age or location. We present a nationally-representative study for dengue from 70 communities in Bangladesh. We collected data on risk factors, trapped mosquitoes and tested serum for IgG. Out of 5866 individuals, 24% had evidence of historic infection, ranging from 3% in the north to >80% in Dhaka. Being male (aOR:1.8, [95%CI:1.5–2.0]) and recent travel (aOR:1.3, [1.1–1.8]) were linked to seropositivity. We estimate that 40 million [34.3–47.2] people have been infected nationally, with 2.4 million ([1.3–4.5]) annual infections. Had we visited only 20 communities, seropositivity estimates would have ranged from 13% to 37%, highlighting the lack of representativeness generated by small numbers of communities. Our findings have implications for both the design of serosurveys and tackling dengue in Bangladesh.

Background Arboviral diseases, including dengue and chikungunya, are major public health concerns in Bangladesh where there have been unprecedented levels of transmission reported in recent years. The primary approach to control these diseases is to control the vector Aedes aegypti using pyrethroid insecticides. Although chemical control has long been practiced, no comprehensive analysis of Ae. aegypti susceptibility to insecticides has been conducted to date. The aim of this study was to determine the insecticide resistance status of Ae. aegypti in Bangladesh and investigate the role of detoxification enzymes and altered target site sensitivity as resistance mechanisms. Methods Eggs of Aedes mosquitoes were collected using ovitraps from five districts across Bangladesh and in eight neighborhoods of the capital city Dhaka, from August to November 2017. CDC bottle bioassays were conducted for permethrin, deltamethrin, malathion, and bendiocarb using 3- to 5-day-old F0–F2 non-blood-fed female mosquitoes. Biochemical assays were conducted to detect metabolic resistance mechanisms, and real-time PCR was performed to determine the frequencies of the knockdown resistance (kdr) mutations Gly1016, Cys1534, and Leu410. Results High levels of resistance to permethrin were detected in all Ae. aegypti populations, with mortality ranging from 0 to 14.8% at the diagnostic dose. Substantial resistance continued to be detected against higher (2×) doses of permethrin (5.1–44.4% mortality). Susceptibility to deltamethrin and malathion varied between populations while complete susceptibility to bendiocarb was observed in all populations. Significantly higher levels of esterase and oxidase activity were detected in most of the test populations as compared to the susceptible reference Rockefeller strain. A significant association was detected between permethrin resistance and the presence of Gly1016 and Cys1534 homozygotes. The frequency of kdr (knockdown resistance) alleles varied across the Dhaka Aedes populations. Leu410 was not detected in any of the tested populations. Conclusions The detection of widespread pyrethroid resistance and multiple resistance mechanisms highlights the urgency for implementing alternate Ae. aegypti control strategies. In addition, implementing routine monitoring of insecticide resistance in Ae. aegypti in Bangladesh will lead to a greater understanding of susceptibility trends over space and time, thereby enabling the development of improved control strategies.

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BackgroundDespite the efforts of the National Malaria Control Programme, malaria remains as an important public health problem in Bangladesh, particularly in the south-eastern region bordering India. Successful malaria control strategies rely on a detailed understanding of the underlying causes of malaria transmission. Here, an entomological survey was conducted in a malaria endemic area of Bangladesh bordering India to investigate the Anopheles mosquito community and assess their Plasmodium infection status.MethodsMonthly entomological collections were undertaken from October 2010 to September 2011 in five villages in the Matiranga sub-district, Khagrachari district in Bangladesh, bordering the Indian State of Tripura. CDC miniature light traps were placed inside houses to collect adult Anopheles mosquitoes. Following morphological and molecular identification of the female Anopheles mosquitoes collected, they were screened for circumsporozoite proteins (CSP) of Plasmodium falciparum (Pf), Plasmodium vivax-210 (Pv-210) and Plasmodium vivax-247 (Pv-247), by ELISA to determine natural infection rates. Variation in Anopheles species composition, relative abundance and Plasmodium infection rates were analysed between sampled villages.ResultsA total of 2,027 female Anopheles were collected, belonging to 20 species. Anopheles nivipes was the most abundant species in our test villages during the peak malaria transmission season, and was observed sympatrically with An. philippinensis in the studied area. However, in the dry off-peak season, An. jeyporiensis was the most abundant species. Shannon’s diversity index was highest in October (2.12) and evenness was highest in May (0.91). The CSP ELISA positive rate overall was 0.44%. Anopheles karwari (n = 2), An. barbirostris s.l. (n = 1) and An. vagus (n = 1) were recorded positive for Pf. Anopheles kochi (n = 1) was positive for Pv-210 while An. umbrosus (n = 1), An. nivipes (n = 1) and An. kochi (n = 1) were positive for Pv-247. A mixed infection of Pf and Pv-247 was detected in An. barbirostris s.l..ConclusionHigh diversity of Anopheles species was observed in areas close to the international border where species that were underestimated for malaria transmission significantly outnumbered principal vector species and these may play a significantly heightened role in malaria transmission.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-015-0803-8) contains supplementary material, which is available to authorized users.

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Malaria is a major health burden in the border-belt areas of Bangladesh. There are recent data from adult mosquito collections that a number of vectors are involved in the transmission cycle. However, little information regarding the larval habitats of Anopheles mosquitoes are available in Bangladesh. To start filling this gap, a cross-sectional larval survey was conducted in Bandarban, Bangladesh from October 2011 to September 2012. Descriptive analysis, Poisson regression, spearman correlations and zero-inflated Poisson regression were used to calculate the degree of association between the abundance of larval Anopheles species and environmental factors. From the 300 larval habitats sampled, 5,568 Anopheles larvae were collected and of these, 2,263 (40.6%) were identified to species. Collections represented 16 Anopheles species with Anopheles vagus (26.4%, n = 598) as the dominant species. A total of 16 Anopheles larval habitat types were identified. Larval abundance was significantly different (P < 0.05) among habitats with pond (40%, n = 914) and rice field (34%, n = 779) implicated to be the most utilized. Larval abundance varied significantly (P < 0.05) with habitat characteristics. Most of the larvae were collected from sites with a range of pH from 7.0 to 8.0. Data obtained from this study revealed both natural and human-created larval habitats were favorable for anopheline larval survival and development. Such information elucidates plausible drivers of high anopheline diversity, high vector abundance, changes in relative species abundance from historic data, and sustained transmission of malaria in endemic areas of Bangladesh.

Food fortification is a cost-effective and sustainable strategy to prevent or correct micronutrient deficiencies. A double-blind cluster (bari) randomised controlled trial was conducted in a rural community in Bangladesh to evaluate the impact of consumption of chapatti made of micronutrient-fortified wheat flour for 6 months by school-aged children on their vitamin A, haemoglobin and iron status. A total of 43 baris (group of households) were randomly selected. The baris were randomly assigned to either intervention or control group. The intervention group received wheat flour fortified with added micronutrients (including 66 mg hydrogen-reduced elemental iron and 3030 mg retinol equivalent as retinyl palmitate per kilogram of flour), while the control group received wheat flour without added micronutrients. A total of 352 children were enrolled in the trial, 203 in the intervention group and 149 in the control group. Analyses were carried out on children who completed the study (191 in the intervention group and 143 in the control group). Micronutrient-fortified wheat flour chapatti significantly increased serum retinol concentration at 6 months by 0.12 mmol L -1 [95% confidence interval (CI): 0.06, 0.19; P < 0.01]. The odds of vitamin A deficiency was significantly lower for children in the intervention group at 3 months [odds ratio (OR) = 0.26; 95% confidence interval (CI): 0.07, 0.89; P < 0.05] and 6 months (OR = 0.21; 95% CI: 0.06, 0.68; P < 0.01). No demonstrable effect of fortified chapatti consumption on iron status, haemoglobin levels or anaemia was observed. Consumption of fortified chapattis demonstrated a significant improvement in the vitamin A status, but not in iron, haemoglobin or anaemia status.

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