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, 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.

Socio-demographic factors influencing knowledge, attitude and practice (KAP) regarding malaria in Bangladesh.

BACKGROUND: A clear understanding of the social and behavioral risk factors, and knowledge gaps, related to exposure to malaria are essential when developing guidelines and recommendations for more effective disease prevention in many malaria endemic areas of the world including Bangladesh and elsewhere in the South East Asia. To-date, the level of knowledge that human populations, residing in moderate to high malaria risk zones, have with respect to the basic pathogen transmission dynamics, risk factors for malaria or disease preventative strategies, has not been assessed in Bangladesh. The purpose of this study was to address this gap by conducting surveys of the knowledge, attitudes and practices (KAP) of people, from variable socio-demographic backgrounds, residing in selected rural malaria endemic areas in Bangladesh. METHODS: The KAP survey was conducted in portions of six different malaria endemic districts in Bangladesh from July to October 2011. The survey consisted of interviewing residence of these malaria endemic districts using a structured questionnaire and interviewers also completed observational checklists at each household where people were interviewed. The study area was further divided into two zones (1 and 2) based on differences in the physical geography and level of malaria endemicity in the two zones. Data from the questionnaires and observational checklists were analysised using Statistical Package for Social Sciences 16.0 (SPSS, Inc., Chicago, IL, USA). RESULTS: A total of 468 individuals from individual households were interviewed, and most respondents were female. Monthly incomes varied within and among the zones. It was found that 46.4% and 41% of respondents' family had malaria within the past one year in zones 1 and 2, respectively. Nearly 86% of the respondents did not know the exact cause of malaria or the role of Anopheles mosquitoes in the pathogen's transmission. Knowledge on malaria transmission and symptoms of the respondents of zones 1 and 2 were significantly (p<0.01) different. The majority of respondents from both zones believed that bed nets were the main protective measure against malaria, but a significant relationship was not found between the use of bed net and prevalence of malaria. A significant relationship (p<0.05) between level of education with malaria prevalence was found in zone 1. There was a positive correlation between the number of family members and the prevalence of malaria. Houses with walls had a strong positive association with malaria. Approximately 50% of the households of zones 1 and 2 maintained that they suffered from malaria within the last year. A significant association (p<0.01) between malaria and the possession of domestic animals in their houses was found in both zones. People who spent time outside in the evening were more likely to contract malaria than those who did not. CONCLUSION: To address the shortcomings in local knowledge about malaria, health personnel working in malaria endemic areas should be trained to give more appropriate counseling in an effort to change certain deeply entrenched traditional behaviors such as spending time outdoors in the evening, improper use of bed nets and irregular use of insecticides during sleep.

Blood-feeding patterns of Anopheles mosquitoes in a malaria-endemic area of Bangladesh.

BACKGROUND: Blood-feeding patterns of mosquitoes are crucial for incriminating malaria vectors. However, little information is available on the host preferences of Anopheles 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. METHODS: Adult Anopheles 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 Anopheles mosquitoes. RESULTS: In total, 2456 female anopheline mosquitoes representing 21 species were collected from the study area. Anopheles vagus Doenitz (35.71%) was the dominant species followed by An. philippinensis Ludlow (26.67%) and An. minimus 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 (χ(2) test, P < 0.001). Host blood meals were successfully detected from 1318 (53.66%) Anopheles 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 An. baimai Baimaii (80%), followed by An. minimus s.l. (43.64%) and An. annularis Van den Wulp (37.50%). Anopheles baimai (B(i) = 0.63) and An. minimus s.l. (B(i) = 0.24) showed strong relative preferences (B(i)) for humans among all hosts (human, bovine, goats/sheep, and others). Anopheles annularis, An. maculatus s.l. Theobald, and An. pallidus 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. CONCLUSIONS: The observed high anthropophilic nature of An. baimai, An. minimus s.l., and An. annularis 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.