False positivity of circumsporozoite protein (CSP)-ELISA in zoophilic anophelines in Bangladesh

Circumsporozoite protein enzyme-linked immunosorbent assays (CSP-ELISAs) are widely used for malaria vector identification throughout the world. However, several studies have reported false-positive results when using this method. The present study was conducted to estimate the frequency of false positives among anopheline species in malaria endemic areas of Bangladesh. In total, 4724 Anopheles females belonging to 25 species were collected and tested for Plasmodium falciparum, Plasmodium vivax-210, and P. vivax-247 CSP. Initially, 144 samples tested positive using routine CSP-ELISA, but the number of positive results declined to 85 (59%) when the samples were tested after heating at 100°C for 10min to remove false-positive specimens. Ten species, Anopheles annularis, Anopheles baimaii, Anopheles barbirostris, Anopheles jeyporiensis, Anopheles karwari, Anopheles kochi, Anopheles minimus s.l., Anopheles peditaeniatus, Anopheles philippinensis, and Anopheles vagus were CSP-positive. The highest and lowest infection rates were found in An. baimaii (4/25, 16.0%) and An. jeyporiensis (1/139, 0.67%), respectively. A significant correlation was found (regression analysis, R2=0.49, F=8.25, P<0.05) between human blood index results and the true CSP-positive ratios in 15 Anopheles species. We confirmed that false-positive reactions occurred more frequently in zoophilic species. The relatively high proportion of false positives (40%) that was found in this study should warn malaria epidemiologists working in the field to be cautious when interpreting ELISA results. © 2012 Elsevier B.V

False positivity of circumsporozoite protein (CSP)-ELISA in zoophilic anophelines in Bangladesh

Circumsporozoite protein enzyme-linked immunosorbent assays (CSP-ELISAs) are widely used for malaria vector identification throughout the world. However, several studies have reported false-positive results when using this method. The present study was conducted to estimate the frequency of false positives among anopheline species in malaria endemic areas of Bangladesh. In total, 4724 Anopheles females belonging to 25 species were collected and tested for Plasmodium falciparum, Plasmodium vivax-210, and P. vivax-247 CSP. Initially, 144 samples tested positive using routine CSP-ELISA, but the number of positive results declined to 85 (59%) when the samples were tested after heating at 100° C for 10 min to remove false-positive specimens. Ten species, Anopheles annularis, Anopheles baimaii, Anopheles barbirostris, Anopheles jeyporiensis, Anopheles karwari, Anopheles kochi, Anopheles minimus s.l., Anopheles peditaeniatus, Anopheles philippinensis, and Anopheles vagus were CSP-positive. The highest and lowest infection rates were found in A. baimaii (4/25, 16.0%) and A. jeyporiensis (1/139, 0.67%), respectively. A significant correlation was found (regression analysis, R 2 = 0.49, F = 8.25, P < 0.05) between human blood index results and the true CSP-positive ratios in 15 Anopheles species. We confirmed that false-positive reactions occurred more frequently in zoophilic species. The relatively high proportion of false positives (40%) that was found in this study should warn malaria epidemiologists working in the field to be cautious when interpreting ELISA results. © 2012 Elsevier B.V. All rights reserved

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