Adherence to Anti-Malarial Treatment in Malaria Endemic Areas of Bangladesh.

Ensuring adherence to antimalarial treatment is crucial for achieving a radical cure and elimination of malaria, especially in hard-to-reach areas. We conducted this study to assess the current scenario of drug adherence in four endemic sub-districts of Bangladesh. Among 110 enrolled participants, 70% were mono-infected with Plasmodium falciparum and the remaining 30% with P. vivax. The overall treatment adherence frequency was 92.7% (95% CI: 83.0-96.3%). A total of eight participants were found to be nonadherent to treatment and all of them were from Bandarban. Level of nonadherence was equally observed in two age groups: 11-17 and 18+ years. However, male participants (n = 6) were found to be more nonadherent than females (n = 2). Among 7.3% with nonadherence to treatment, a single participant with P. falciparum mono-infection refused to take medication and became nonadherent. Remaining participants stated that they were feeling well and going to work, thus leaving treatment course uncompleted. Although overall compliance with malaria medication seems good, a gradual increase in noncompliance to P. vivax malaria treatment suggests that the National Malaria Elimination Program must be enhanced and monitored to fulfil the projected malaria elimination goal before 2030 from Bangladesh.

Host Selection of Field-Collected Anopheles jeyporiensis and Anopheles nivipes in Bangladesh.

Anopheles jeyporiensis and Anopheles nivipes appear to play an important role in contemporary malaria transmission in Bangladesh. However, very little is known about the natural host selection of these vectors. Therefore, host selection of these two species was investigated in Bandarban, the most malarious region of Bangladesh. A total of 480 engorged mosquitoes were analyzed. The human blood index (HBI) of An. jeyporiensis varied from 4.17% in outdoor to 19.17% in indoor collections. Similarly, HBI of An. nivipes ranged between 0.83% and 22.50% from outdoor to indoor. For both species, cow blood indices were significantly higher than HBI in both indoor and outdoor collections. These data demonstrate the opportunistic and zoophilic nature of An. jeyporiensis and An. nivipes, which suggests that approaches such as zooprophylasis may prove beneficial as a control strategy.

Abundance and Dynamics of Anopheles (Diptera: Culicidae) Larvae in a Malaria Endemic Area of Bangladesh.

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.

Sampling Design Influences the Observed Dominance of Culex tritaeniorhynchus: Considerations for Future Studies of Japanese Encephalitis Virus Transmission.

Mosquito sampling during Japanese encephalitis virus (JEV)-associated studies, particularly in India, has usually been conducted via aspirators or light traps to catch mosquitoes around cattle, which are dead-end hosts for JEV. High numbers of Culex tritaeniorhynchus, relative to other species, have often been caught during these studies. Less frequently, studies have involved sampling outdoor resting mosquitoes. We aimed to compare the relative abundance of mosquito species between these two previously used mosquito sampling methods. From September to December 2013 entomological surveys were undertaken in eight villages in a Japanese encephalitis (JE) endemic area of Bangladesh. Light traps were used to collect active mosquitoes in households, and resting boxes and a Bina Pani Das hop cage were used near oviposition sites to collect resting mosquitoes. Numbers of humans and domestic animals present in households where light traps were set were recorded. In five villages Cx. tritaeniorhynchus was more likely to be selected from light trap samples near hosts than resting collection samples near oviposition sites, according to log odds ratio tests. The opposite was true for Cx. pseudovishnui and Armigeres subalbatus, which can also transmit JEV. Culex tritaeniorhynchus constituted 59% of the mosquitoes sampled from households with cattle, 28% from households without cattle and 17% in resting collections. In contrast Cx. pseudovishnui constituted 5.4% of the sample from households with cattle, 16% from households with no cattle and 27% from resting collections, while Ar. subalbatus constituted 0.15%, 0.38%, and 8.4% of these samples respectively. These observations may be due to differences in timing of biting activity, host preference and host-seeking strategy rather than differences in population density. We suggest that future studies aiming to implicate vector species in transmission of JEV should consider focusing catches around hosts able to transmit JEV.

Role of underappreciated vectors in malaria transmission in an endemic region of Bangladesh-India border.

BACKGROUND: Despite 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. METHODS: Monthly 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. RESULTS: A 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.. CONCLUSION: High 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.

Diversity of anopheline species and their Plasmodium infection status in rural Bandarban, Bangladesh.

BACKGROUND: Historically, the Chittagong Hill Tracts (CHT) of Bangladesh was considered hyperendemic for malaria. To better understand the contemporary malaria epidemiology and to develop new and innovative control strategies, comprehensive epidemiologic studies are ongoing in two endemic unions of Bandarban district of CHT. Within these studies entomological surveillance has been undertaken to study the role of the existing anopheline species involved in the malaria transmission cycle throughout the year. METHODS: CDC miniature light traps were deployed to collect anopheline mosquitoes from the sleeping room of the selected houses each month in a single union (Kuhalong). Molecular identification was carried out for available Anopheles species complexes. Circumsporozoite proteins (CSP) for Plasmodium falciparum, Plasmodium vivax-210 (Pv-210) and Plasmodium vivax-247(Pv-247) were detected by Enzyme-linked immunosorbent assay (ELISA) from the female anopheline mosquitoes. To confirm CSP-ELISA results, polymerase chain reaction (PCR) was also performed. RESULTS: A total of 2,837 anopheline mosquitoes, of which 2,576 were female, belonging to 20 species were collected from July 2009-June 2010. Anopheles jeyporiensis was the most abundant species (18.9%), followed by An. vagus (16.8%) and An. kochi (14.4%). ELISA was performed on 2,467 female mosquitoes of 19 species. 15 (0.6%) female anophelines belonging to eight species were found to be positive for Plasmodium infection by CSP-ELISA. Of those, 11 (0.4%) mosquitoes were positive for P. falciparum and four (0.2%) for Pv-210. No mosquito was found positive for Pv-247. An. maculatus (2.1%, 2/97) had the highest infection rate followed by An. umbrosus (1.7%, 2/115) and An. barbirostris (1.1%, 2/186). Other infected species were An. nigerrimus, An. nivipes, An. jeyporiensis, An. kochi, and An. vagus. Out of 11 P. falciparum CSP positive samples, seven turned out to be positive by PCR. None of the samples positive for Pv-210 was positive by PCR. In terms of abundance and incrimination, the results suggest that An. maculatus, An. jeyporiensis and An. nivipes play important roles in malaria transmission in Kuhalong. CONCLUSION: The findings of this study suggest that even in the presence of an insecticide impregnated bed-net intervention, a number of Anopheles species still play a role in the transmission of malaria. Further investigations are required to reveal the detailed biology and insecticide resistance patterns of the vector mosquito species in endemic areas in Bangladesh in order to assist with the planning and implementation of improved malaria control strategies.