Prevalence of anopheline species and their Plasmodium infection status in epidemic-prone border areas of Bangladesh

<p>Abstract</p> <p>Background</p> <p>Information related to malaria vectors is very limited in Bangladesh. In the changing environment and various <it>Anopheles </it>species may be incriminated and play role in the transmission cycle. This study was designed with an intention to identify anopheline species and possible malaria vectors in the border belt areas, where the malaria is endemic in Bangladesh.</p> <p>Methods</p> <p><it>Anopheles </it>mosquitoes were collected from three border belt areas (Lengura, Deorgachh and Matiranga) during the peak malaria transmission season (May to August). Three different methods were used: human landing catches, resting collecting by mouth aspirator and CDC light traps. Enzyme-linked immunosorbent assay (ELISA) was done to detect <it>Plasmodium falciparum</it>, <it>Plasmodium vivax</it>-210 and <it>Plasmodium vivax</it>-247 circumsporozoite proteins (CSP) from the collected female species.</p> <p>Results</p> <p>A total of 634 female <it>Anopheles </it>mosquitoes belonging to 17 species were collected. <it>Anopheles vagus </it>(was the dominant species (18.6%) followed by <it>Anopheles nigerrimus </it>(14.5%) and <it>Anopheles philippinensis </it>(11.0%). Infection rate was found 2.6% within 622 mosquitoes tested with CSP-ELISA. Eight (1.3%) mosquitoes belonging to five species were positive for <it>P. falciparum</it>, seven (1.1%) mosquitoes belonging to five species were positive for <it>P. vivax </it>-210 and a single mosquito (0.2%) identified as <it>Anopheles maculatus </it>was positive for <it>P. vivax</it>-247. No mixed infection was found. Highest infection rate was found in <it>Anopheles karwari </it>(22.2%) followed by <it>An. maculatus </it>(14.3%) and <it>Anopheles barbirostris </it>(9.5%). Other positive species were <it>An. nigerrimus </it>(4.4%), <it>An. vagus </it>(4.3%), <it>Anopheles subpictus </it>(1.5%) and <it>An. philippinensis </it>(1.4%). <it>Anopheles vagus </it>and <it>An. philippinensis </it>were previously incriminated as malaria vector in Bangladesh. In contrast, <it>An. karwari</it>, <it>An. maculatus</it>, <it>An. barbirostris</it>, <it>An. nigerrimus </it>and <it>An. subpictus </it>had never previously been incriminated in Bangladesh.</p> <p>Conclusion</p> <p>Findings of this study suggested that in absence of major malaria vectors there is a possibility that other <it>Anopheles </it>species may have been playing role in malaria transmission in Bangladesh. Therefore, further studies are required with the positive mosquito species found in this study to investigate their possible role in malaria transmission in Bangladesh.</p

The dominant Anopheles vectors of human malaria in the Asia-Pacific region: occurrence data, distribution maps and bionomic précis

<p>Abstract</p> <p>Background</p> <p>The final article in a series of three publications examining the global distribution of 41 dominant vector species (DVS) of malaria is presented here. The first publication examined the DVS from the Americas, with the second covering those species present in Africa, Europe and the Middle East. Here we discuss the 19 DVS of the Asian-Pacific region. This region experiences a high diversity of vector species, many occurring sympatrically, which, combined with the occurrence of a high number of species complexes and suspected species complexes, and behavioural plasticity of many of these major vectors, adds a level of entomological complexity not comparable elsewhere globally. To try and untangle the intricacy of the vectors of this region and to increase the effectiveness of vector control interventions, an understanding of the contemporary distribution of each species, combined with a synthesis of the current knowledge of their behaviour and ecology is needed.</p> <p>Results</p> <p>Expert opinion (EO) range maps, created with the most up-to-date expert knowledge of each DVS distribution, were combined with a contemporary database of occurrence data and a suite of open access, environmental and climatic variables. Using the Boosted Regression Tree (BRT) modelling method, distribution maps of each DVS were produced. The occurrence data were abstracted from the formal, published literature, plus other relevant sources, resulting in the collation of DVS occurrence at 10116 locations across 31 countries, of which 8853 were successfully geo-referenced and 7430 were resolved to spatial areas that could be included in the BRT model. A detailed summary of the information on the bionomics of each species and species complex is also presented.</p> <p>Conclusions</p> <p>This article concludes a project aimed to establish the contemporary global distribution of the DVS of malaria. The three articles produced are intended as a detailed reference for scientists continuing research into the aspects of taxonomy, biology and ecology relevant to species-specific vector control. This research is particularly relevant to help unravel the complicated taxonomic status, ecology and epidemiology of the vectors of the Asia-Pacific region. All the occurrence data, predictive maps and EO-shape files generated during the production of these publications will be made available in the public domain. We hope that this will encourage data sharing to improve future iterations of the distribution maps.</p

Blood-feeding patterns of <it>Anopheles </it>mosquitoes in a malaria-endemic area of Bangladesh

<p>Abstract</p> <p>Background</p> <p>Blood-feeding patterns of mosquitoes are crucial for incriminating malaria vectors. However, little information is available on the host preferences of <it>Anopheles </it>mosquitoes in Bangladesh. Therefore, the objective of the present study was to determine the hematophagic tendencies of the anophelines inhabiting a malaria-endemic area of Bangladesh.</p> <p>Methods</p> <p>Adult <it>Anopheles </it>mosquitoes were collected using light traps (LTs), pyrethrum spray (PS), and human bait (HB) from a malaria-endemic village (Kumari, Bandarban, Bangladesh) during the peak months of malaria transmission (August-September). Enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) were performed to identify the host blood meals of <it>Anopheles </it>mosquitoes.</p> <p>Results</p> <p>In total, 2456 female anopheline mosquitoes representing 21 species were collected from the study area. <it>Anopheles vagus </it>Doenitz (35.71%) was the dominant species followed by <it>An. philippinensis </it>Ludlow (26.67%) and <it>An. minimus </it>s.l. Theobald (5.78%). All species were collected by LTs set indoors (n = 1094), 19 species were from outdoors (n = 784), whereas, six by PS (n = 549) and four species by HB (n = 29). Anopheline species composition significantly differed between every possible combination of the three collection methods (χ²test, P < 0.001). Host blood meals were successfully detected from 1318 (53.66%) <it>Anopheles </it>samples belonging to 17 species. Values of the human blood index (HBI) of anophelines collected from indoors and outdoors were 6.96% and 11.73%, respectively. The highest values of HBI were found in <it>An. baimai </it>Baimaii (80%), followed by <it>An. minimus </it>s.l. (43.64%) and <it>An. annularis </it>Van den Wulp (37.50%). <it>Anopheles baimai </it>(<it>B_i</it>= 0.63) and <it>An. minimus </it>s.l. (<it>B_i</it>= 0.24) showed strong relative preferences (<it>B_i</it>) for humans among all hosts (human, bovine, goats/sheep, and others). <it>Anopheles annularis</it>, <it>An. maculatus </it>s.l. Theobald, and <it>An. pallidus </it>Theobald exhibited opportunistic blood-feeding behavior, in that they fed on either humans or animals, depending on whichever was accessible. The remaining 12 species preferred bovines as hosts.</p> <p>Conclusions</p> <p>The observed high anthropophilic nature of <it>An. baimai</it>, <it>An. minimus </it>s.l., and <it>An. annularis </it>revealed these species to be important malaria vectors in hilly areas of Bangladesh. Higher values of HBI in outdoor-resting mosquitoes indicated that indoor collection alone is not adequate for evaluating malaria transmission in the area.</p

Behavioural heterogeneity of Anopheles species in ecologically different localities in Southeast Asia: a challenge for vector control

The definitive version is available at www3.interscience.wiley.comIn Southeast Asia the biodiversity of Anopheles species in the domestic environment is very high. Only few species are considered major vectors throughout the region, whereas the vector status of other species varies from area to area. Often it is difficult to identify an Anopheles species as a malaria vector in areas with low malaria incidence. The behaviour of Anopheles species largely determines their vector status, and insights into their behaviour are essential to evaluate the appropriateness of vector control measures. This study was conducted in six ecologically different localities in Southeast Asia to rank the different Anopheles species in terms of anthropophily and endophagy in order to estimate their current epidemiological importance. Concurrently, the biting and resting behaviour of the vectors was analysed to evaluate the appropriateness of insecticide-impregnated bed nets and residual house spraying in vector control. Anopheles dirus A was highly anthropophilic at all sites where it occurred. By contrast, the degree of anthropophily exhibited by An. minimus A depended on availability of cattle. Anopheles campestris, An. nimpe, An. sinensis, An. maculatus, An. aconitus showed a high degree of anthropophily in certain villages, indicating their potential of participating in malaria transmission, although the actual incidence of malaria in the study villages can be fully explained by transmission of the major vectors (An. dirus A, An. minimus A and An. sundaicus). Late biting of An. minimus A and biting activity throughout the night of An. sundaicus favour bed nets as a control method for these species, whilst exophilic and outdoor biting in combination with early feeding behaviour of An. dirus A will make both insecticide-impregnated bed nets and indoor residual spraying less suitable for controlling this species. Spatial variation in biting and resting behaviour was observed within almost all Anopheles species. These heterogeneities may result in the differences in epidemiological importance and in response to vector control of Anopheles species in different areas. Moreover, environmental changes and changes in human practice are expected to influence the behaviour, hence the role of the different species in malaria transmission. The effect of environmental changes on vector behaviour should be followed up carefully

Diversity of anopheline species and their <it>Plasmodium</it> infection status in rural Bandarban, Bangladesh

<p>Abstract</p> <p>Background</p> <p>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.</p> <p>Methods</p> <p>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 <it>Anopheles</it> species complexes. Circumsporozoite proteins (CSP) for <it>Plasmodium falciparum</it>, <it>Plasmodium vivax</it>-210 (Pv-210) and <it>Plasmodium vivax</it>-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.</p> <p>Results</p> <p>A total of 2,837 anopheline mosquitoes, of which 2,576 were female, belonging to 20 species were collected from July 2009 -June 2010. <it>Anopheles jeyporiensis</it> was the most abundant species (18.9%), followed by <it>An. vagus</it> (16.8%) and <it>An. kochi</it> (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 <it>Plasmodium</it> infection by CSP-ELISA. Of those, 11 (0.4%) mosquitoes were positive for <it>P. falciparum</it> and four (0.2%) for Pv-210. No mosquito was found positive for Pv-247. <it>An. maculatus</it> (2.1%, 2/97) had the highest infection rate followed by <it>An. umbrosus</it> (1.7%, 2/115) and <it>An. barbirostris</it> (1.1%, 2/186). Other infected species were <it>An. nigerrimus</it>, <it>An. nivipes, An. jeyporiensis</it>, <it>An. kochi</it>, and <it>An. vagus</it>. Out of 11 <it>P. falciparum</it> 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 <it>An. maculatus</it>, <it>An. jeyporiensis</it> and <it>An. nivipes</it> play important roles in malaria transmission in Kuhalong.</p> <p>Conclusion</p> <p>The findings of this study suggest that even in the presence of an insecticide impregnated bed-net intervention, a number of <it>Anopheles</it> 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.</p