Mosquito biting activity on humans & detection of Plasmodium falciparum infection in Anopheles stephensi in Goa, India

Circadian rhythms mediate malaria transmission potential

Malaria transmission begins when infected female Anopheles mosquitos deposit Plasmodium parasites into the mammalian host's skin during a bloodmeal. The salivary gland-resident sporozoite parasites migrate to the bloodstream, subsequently invading and replicating within hepatocytes. As Anopheles mosquitos are more active at night, with a 24-hour rhythm, we investigated whether their salivary glands are under circadian control, anticipating bloodmeals and modulating sporozoite biology for host encounters. Here we show that approximately half of the mosquito salivary gland transcriptome, particularly genes essential for efficient bloodmeals such as anti-blood clotting factors, exhibits circadian rhythmic expression. Furthermore, we demonstrate that mosquitoes prefer to feed during nighttime, with the amount of blood ingested varying cyclically throughout the day. Notably, we show a substantial subset of the sporozoite transcriptome cycling throughout the day. These include genes involved in parasite motility, potentially modulating the ability to initiate infection at different times of day. Thus, although sporozoites are typically considered quiescent, our results demonstrate their transcriptional activity, revealing robust daily rhythms of gene expression. Our findings suggest a circadian evolutionary relationship between the vector, parasite and mammalian host that together modulate malaria transmission.

Decline of Malaria Incidence in Three Villages of Thar Desert, India: The Impact of Use of Insecticide-Treated Nets

Background

Malaria is the most important tropical and parasitic disease in the world. Endophagy of many malaria vectors advocates that impeding their entry into houses and preventing their contact with the occupants from infective bites could protect them against malaria.

Methods

The study was carried out in Jaisalmer District, India and three villages were selected as test villages and three as control. Cross-sectional malaria prevalence surveys and mosquito collections were conducted in all the study villages. Insecticide-treated nets (ITNs) were tied below the beds for personal protection against the mosquito bite. Door and window curtains along with partition curtains were treated with insecticide for baring the entry of mosquito vectors.

Results

Plasmodium vivax and P. falciparum were reported from the study villages. Higher malaria cases were detected in the control villages than the insecticide-treated bed net-distributed villages. The percentages of reduction of mosquito density in the houses of the ITNs distributed villages were significantly higher than the control villages. The insecticide activity was decreased slowly, and the knockdown time (KD50) values were found to be increased with the duration of usage of net. The KD50 of Anopheles subpictus s.l. was found to be more than the An. stephensi. Rooms where the ITNs were found to be significantly lower per man-hour density of mosquitoes.

Conclusion

The use of alternative forms of ITNs shows a potential for preventing malaria and are making a significant contribution to the mosquito control. Effective use of ITNs could be helpful in the malaria elimination in India by 2030.

Seasonal dynamics of Anopheles stephensi and its implications for mosquito detection and emergent malaria control in the Horn of Africa

Invasion of the malaria vector Anopheles stephensi across the Horn of Africa threatens control efforts across the continent, particularly in urban settings where the vector is able to proliferate. Malaria transmission is primarily determined by the abundance of dominant vectors, which often varies seasonally with rainfall. However, it remains unclear how An. stephensi abundance changes throughout the year, despite this being a crucial input to surveillance and control activities. We collate longitudinal catch data from across its endemic range to better understand the vector's seasonal dynamics and explore the implications of this seasonality for malaria surveillance and control across the Horn of Africa. Our analyses reveal pronounced variation in seasonal dynamics, the timing and nature of which are poorly predicted by rainfall patterns. Instead, they are associated with temperature and patterns of land use; frequently differing between rural and urban settings. Our results show that timing entomological surveys to coincide with rainy periods is unlikely to improve the likelihood of detecting An. stephensi. Integrating these results into a malaria transmission model, we show that timing indoor residual spraying campaigns to coincide with peak rainfall offers little improvement in reducing disease burden compared to starting in a random month. Our results suggest that unlike other malaria vectors in Africa, rainfall may be a poor guide to predicting the timing of peaks in An. stephensi-driven malaria transmission. This highlights the urgent need for longitudinal entomological monitoring of the vector in its new environments given recent invasion and potential spread across the continent.

Challenges in Understanding the Bionomics of Indian Malaria Vectors

Many factors influence the success or failure of malaria vector control program such as political will, leadership, sustained funding, robustness of healthcare system and others. In addition, updated knowledge and information about the triad of host, parasite, and vector is of paramount importance. Vector bionomics studies that determine mosquito behavior in terms of feeding, resting, biting, mating, breeding, longevity, vectorial capacity, and response to different insecticides are a step towards enhancing our understanding. In the present work, we have compiled studies conducted in India over the past two decades (2000-2020) to identify gaps in our knowledge of malaria vector bionomics and the research that needs to be done in the future. We retrieved district-level data of India's six primary malaria vector species. According to our findings, vector bionomics studies have been undertaken in ∼50% and ∼15% of the country's high (annual parasite index > 1) and low (annual parasite index < 1) malaria-endemic districts respectively. Most of the research studies focused on mosquito density, insecticide susceptibility status, and parasite detection, whereas other vital bionomics parameters were neglected. Surveys conducted were incomplete, and vector bionomics data were not captured sufficiently. The absence of vector bionomics data can be a blind spot and the lack or inadequate understanding of vector bionomics can lead to use of inappropriate vector control tools. Thus, there is an urgent need to initiate comprehensive bionomics studies on India's primary and secondary malaria vectors.

Insecticidal effects of some selected plant extracts against Anopheles stephensi (Culicidae: Diptera)

BACKGROUND

The use of synthetic insecticides against mosquitoes may lead to resistance development and potential health hazards in humans and the environment. Consequently, a paradigm needs to shift towards the alternative use of botanical insecticides that could strengthen an insecticide resistance management programme. This study aimed to assess the insecticidal effects aqueous, hexane, and methanol crude leaf extracts of Calpurnia aurea, Momordica foetida, and Zehneria scabra on an insectary colony of Anopheles stephensi larvae and adults.

METHODS

Fresh leaves of C. aurea, M. foetida and Z. scabra were collected and dried, then separately ground to powder. Powdered leaves of test plants were extracted using sonication with aqueous, hexane, and methanol solvents. The extracts were concentrated, and a stock solution was prepared. For comparison, Temephos (Abate®) and control solutions (a mixture of water and emulsifier) were used as the positive and negative controls, respectively. Different test concentrations for the larvae and the adults were prepared and tested according to WHO (2005) and CDC (2010) guidelines to determine lethal concentration (LC) values. Mortality was observed after 24 h exposure. The statistical analyses were performed using Statistical Package for the Social Sciences (SPSS) software (Kruskal-Wallis test) and R software (a generalized linear model was used to determine LC₅₀ and LC₉₀ values of the extracts).

RESULTS

The lowest LC₅₀ values were observed in aqueous extracts of M. foetida followed by Z. scabra extract and C. aurea leaves at 34.61, 35.85, and 38.69 ppm, respectively, against the larvae. Larval mortality was not observed from the hexane extracts and negative control, while the standard larvicide (temephos) achieved 100% mortality. Further, the adulticidal efficacy was greatest for aqueous extract of Z. scabra with LC₅₀ = 176.20 ppm followed by aqueous extract of C. aurea (LC₅₀ = 297.75 ppm).

CONCLUSION

The results suggest that the leaf extracts of the three test plants have the potential of being used for the control of vector An. stephensi larvae and adult instead of synthetic mosquitocides. Further studies need to be conducted to identify the active ingredients and their mode of action.

Insecticidal effects of a novel polyherbal formulation (HF7) against Culex pipiens L. (Diptera: Culicidae)

Plant secondary metabolites represent the most efficient and convenient method to control and overcome environmental pollution and insecticidal resistance. This study explored the mosquitocidal activity of the combined extract of seven plants, (HF7) extracted using a Soxhlet extractor against Culex pipiens under laboratory conditions. Exposure of the 3rd instars of Cx. pipiens to HF7 hexane extract resulted in LC₅₀:114.5 μg/mL and LC₉₀:117.0 μg/mL values after 24 h. The ovicidal activities of hexane extract against Cx. pipiens eggs were 21.6%, 48.3%, and 71.6% at 187.5, 93.7, and 46.88 μg/mL, respectively. HF7-treated larvae showed the formation of irregular blebbing of epithelial cells toward the lumen and sloughing into the gut lumen. HF7 extract resulted in 100% adulticidal mortality at the concentration of 3.7 mg/test tube after 30 min of exposure. The IC₅₀ of HF7 extract was 97.03 µg/ml against larvae, at which nuclear and morphological changes were observed. The spectroscopy spectrum of HF7 hexane extract disclosed the presence of 57 different secondary metabolites, among which the dominant compound was eugenol (32.3%). HF7 hexane extract could serve as a botanical insecticide for controlling Cx. pipiens and potentially other mosquito species.

Geographical distribution of Anopheles stephensi in eastern Ethiopia

Background

The recent detection of the South Asian malaria vector Anopheles stephensi in Ethiopia and other regions in the Horn of Africa has raised concerns about its potential impact on malaria transmission. We report here the findings of a survey for this species in eastern Ethiopia using both morphological and molecular methods for species identification.

Methods

Adult and larval/pupal collections were conducted at ten sites in eastern Ethiopia and Anopheles specimens were identified using standard morphological keys and genetic analysis.

Results

In total, 2231 morphologically identified An. stephensi were collected. A molecular approach incorporating both PCR endpoint assay and sequencing of portions of the internal transcribed spacer 2 (ITS2) and cytochrome c oxidase subunit 1 (cox1) loci confirmed the identity of the An. stephensi in most cases (119/124 of the morphologically identified An. stephensi confirmed molecularly). Additionally, we observed Aedes aegypti larvae and pupae at many of the An. stephensi larval habitats.

Conclusions

Our findings show that An. stephensi is widely distributed in eastern Ethiopia and highlight the need for further surveillance in the southern, western and northern parts of the country and throughout the Horn of Africa.

Biology and bionomics of malaria vectors in India: existing information and what more needs to be known for strategizing elimination of malaria

India has committed to eliminate malaria by 2030. The national framework for malaria elimination released by the Government of India plans to achieve this goal through strategic planning in a phased manner. Since vector control is a major component of disease management and vector elimination, it requires a thorough understanding of the biology and bionomics of malaria vectors exhibiting definite distribution patterns in diverse ecosystems in the country. Although a wealth of information is available on these aspects, lesser-known data are on biting time and rhythm, and the magnitude of outdoor transmission by the vectors which are crucial for effective implementation of the key vector control interventions. Most of the data available for the vector species are at sensu lato level, while the major vectors are species complexes and their members distinctly differ in biological characters. Furthermore, the persistent use of insecticides in indoor residual spray and long-lasting insecticidal nets has resulted in widespread resistance in vectors and changes in their behaviour. In this document, challenges in vector control in the Indian context have been identified and possible solutions to overcome the problem are suggested. Adequate addressing of the issues raised would greatly help make a deep dent in malaria transmission and consequently result in disease elimination within the targeted time frame.

Time-of-day of blood-feeding: effects on mosquito life history and malaria transmission

BACKGROUND

Biological rhythms allow organisms to compartmentalise and coordinate behaviours, physiologies, and cellular processes with the predictable daily rhythms of their environment. There is increasing recognition that the biological rhythms of mosquitoes that vector parasites are important for global health. For example, whether perturbations in blood foraging rhythms as a consequence of vector control measures can undermine disease control. To address this, we explore the impacts of altered timing of blood-feeding on mosquito life history traits and malaria transmission.

METHODS

We present three experiments in which Anopheles stephensi mosquitoes were fed in the morning or evening on blood that had different qualities, including: (i) chemical-induced or (ii) Plasmodium chabaudi infection-induced anaemia; (iii) Plasmodium berghei infection but no anaemia; or (iv) stemming from hosts at different times of day. We then compared whether time-of-day variation in blood meal characteristics influences mosquito fitness proxies relating to survival and reproduction, and malaria transmission proxies.

RESULTS

Mosquito lifespan is not influenced by the time-of-day they received a blood meal, but several reproductive metrics are affected, depending on other blood characteristics. Overall, our data suggest that receiving a blood meal in the morning makes mosquitoes more likely to lay eggs, lay slightly sooner and have a larger clutch size. In keeping with previous work, P. berghei infection reduces mosquito lifespan and the likelihood of laying eggs, but time-of-day of blood-feeding does not impact upon these metrics nor on transmission of this parasite.

CONCLUSION

The time-of-day of blood-feeding does not appear to have major consequences for mosquito fitness or transmission of asynchronous malaria species. If our results from a laboratory colony of mosquitoes living in benign conditions hold for wild mosquitoes, it suggests that mosquitoes have sufficient flexibility in their physiology to cope with changes in biting time induced by evading insecticide-treated bed nets. Future work should consider the impact of multiple feeding cycles and the abiotic stresses imposed by the need to forage for blood during times of day when hosts are not protected by bed nets.

Daily oscillations in expression and responsiveness of Toll-like receptors in splenic immune cells

Circadian rhythms refer to biologic processes that oscillate with an approximate 24-h period. These rhythms direct nearly all aspects of animal behavior and physiology. The aim of our study was to determine if Toll-like receptor (TLR) expression and responsiveness exhibit time-of-day dependent differences. Therefore, we isolated an adherent splenocyte population, which consisted primarily of B cells, dendritic cells, and macrophages, over the course of a 24-h light-dark period and measured daily changes in Tlr1-8 mRNA levels and cytokine expression after cells were challenged at Zeitgeber time (ZT) 1 or ZT13 with a TLR ligand. In addition, we assessed TLR3 protein levels in adherent splenocytes over the 24-h light-dark period and challenged mice at ZT1 or ZT13 with poly(I:C), the TLR3 ligand. Our study revealed that in this adherent cell population, all Tlrs exhibited rhythmic expression except Tlr2 and Tlr5, and all TLRs, except TLR8, demonstrated daily variations in responsiveness after challenge with their respective ligand. We also revealed that TLR3 protein levels fluctuate over the daily light-dark cycle in adherent splenocytes and mice exhibit a time-of-day dependent immune response when challenged with poly(I:C). Finally, we demonstrated that mRNA levels of Tlr2 and Tlr6 display rhythmic expression in splenic macrophages. Taken together, these findings could have important implications for TLR-directed therapeutics.

Quantifying seasonal and diel variation in Anopheline and Culex human biting rates in Southern Ecuador

BACKGROUND

Quantifying mosquito biting rates for specific locations enables estimation of mosquito-borne disease risk, and can inform intervention efforts. Measuring biting itself is fraught with ethical concerns, so the landing rate of mosquitoes on humans is often used as a proxy measure. Southern coastal Ecuador was historically endemic for malaria (Plasmodium falciparum and Plasmodium vivax), although successful control efforts in the 2000s eliminated autochthonous transmission (since 2011). This study presents an analysis of data collected during the elimination period.

METHODS

Human landing catch (HLC) data for three mosquito taxa: two malaria vectors, Anopheles albimanus and Anopheles punctimacula, and grouped Culex spp. were examined for this study. These data were collected by the National Vector Control Service of the Ministry of Health over a 5-year time span (2007-2012) in five cities in southern coastal Ecuador, at multiple households, in all months of the year, during dusk-dawn (18:00-6:00) hours, often at both indoor and outdoor locations. Hurdle models were used to determine if biting activity was fundamentally different for the three taxa, and to identify spatial and temporal factors influencing bite rate. Due to the many different approaches to studying and quantifying bite rates in the literature, a glossary of terms was created, to facilitate comparative studies in the future.

RESULTS

Biting trends varied significantly with species and time. All taxa exhibited exophagic feeding behavior, and outdoor locations increased both the odds and incidence of bites across taxa. Anopheles albimanus was most frequently observed biting, with an average of 4.7 bites/h. The highest and lowest respective months for significant biting activity were March and July for An. albimanus, July and August for An. punctimacula, and February and July for Culex spp.

CONCLUSIONS

Fine-scale differences in endophagy and exophagy, and temporal differences among months and hours exist in biting patterns among mosquito taxa in southern coastal Ecuador. This analysis provides detailed information for targeting vector control activities, and household level vector prevention strategies. These data were collected as part of routine vector surveillance conducted by the Ministry of Health, and such data have not been collected since. Reinstating such surveillance measures would provide important information to aid in preventing malaria re-emergence.

Anopheles subpictus carry human malaria parasites in an urban area of Western India and may facilitate perennial malaria transmission

Background

India contributes 1.5–2 million annual confirmed cases of malaria. Since both parasites and vectors are evolving rapidly, updated information on parasite prevalence in mosquitoes is important for vector management and disease control. Possible new vector-parasite interactions in Goa, India were tested.

Methods

A total of 1036 CDC traps were placed at four malaria endemic foci in Goa, India from May 2013 to April 2015. These captured 23,782 mosquitoes, of which there were 1375 female anopheline specimens with ten species identified using morphological keys. Mosquito DNA was analysed for human and bovine blood as well as for Plasmodium falciparum and Plasmodium vivax infection.

Results

Human host feeding was confirmed in Anopheles stephensi (30 %), Anopheles subpictus (27 %), Anopheles jamesii (22 %), Anopheles annularis (26 %), and Anopheles nigerrimus (16 %). In contrast, Anopheles vagus, Anopheles barbirostris, Anopheles tessellates, Anopheles umbrosus and Anopheles karwari specimens were negative for human blood. Importantly, An. subpictus, which was considered a non-vector in Goa and Western India, was found to be a dominant vector in terms of both total number of mosquitoes collected as well as Plasmodium carriage. Plasmodium infections were detected in 14 An. subpictus (2.8 %), while the traditional vector, An. stephensi, showed seven total infections, two of which were in the salivary glands. Of the 14 An. subpictus infections, nested PCR demonstrated three Plasmodium infections in the salivary glands: one P. vivax and two mixed infections of P. falciparum and P. vivax. In addition, ten gut infections (one P. vivax, six P. falciparum and three mixed infections) were seen in An. subpictus. Longitudinal mosquito collections pointed to a bimodal annual appearance of An. subpictus to maintain a perennial malaria transmission cycle of both P. vivax and P. falciparum in Goa.

Entomological Monitoring and Evaluation: Diverse Transmission Settings of ICEMR Projects Will Require Local and Regional Malaria Elimination Strategies

The unprecedented global efforts for malaria elimination in the past decade have resulted in altered vectorial systems, vector behaviors, and bionomics. These changes combined with increasingly evident heterogeneities in malaria transmission require innovative vector control strategies in addition to the established practices of long-lasting insecticidal nets and indoor residual spraying. Integrated vector management will require focal and tailored vector control to achieve malaria elimination. This switch of emphasis from universal coverage to universal coverage plus additional interventions will be reliant on improved entomological monitoring and evaluation. In 2010, the National Institutes for Allergies and Infectious Diseases (NIAID) established a network of malaria research centers termed ICEMRs (International Centers for Excellence in Malaria Research) expressly to develop this evidence base in diverse malaria endemic settings. In this article, we contrast the differing ecology and transmission settings across the ICEMR study locations. In South America, Africa, and Asia, vector biologists are already dealing with many of the issues of pushing to elimination such as highly focal transmission, proportionate increase in the importance of outdoor and crepuscular biting, vector species complexity, and "sub patent" vector transmission.

Urban Malaria: Understanding its Epidemiology, Ecology, and Transmission Across Seven Diverse ICEMR Network Sites

A major public health question is whether urbanization will transform malaria from a rural to an urban disease. However, differences about definitions of urban settings, urban malaria, and whether malaria control should differ between rural and urban areas complicate both the analysis of available data and the development of intervention strategies. This report examines the approach of the International Centers of Excellence for Malaria Research (ICEMR) to urban malaria in Brazil, Colombia, India (Chennai and Goa), Malawi, Senegal, and Uganda. Its major theme is the need to determine whether cases diagnosed in urban areas were imported from surrounding rural areas or resulted from transmission within the urban area. If infections are being acquired within urban areas, malaria control measures must be targeted within those urban areas to be effective. Conversely, if malaria cases are being imported from rural areas, control measures must be directed at vectors, breeding sites, and infected humans in those rural areas. Similar interventions must be directed differently if infections were acquired within urban areas. The hypothesis underlying the ICEMR approach to urban malaria is that optimal control of urban malaria depends on accurate epidemiologic and entomologic information about transmission.

Anopheline species and their Plasmodium infection status in Aligarh, India

Malaria is a global issue and India contributes substantially to global malaria incidence. Information related to malaria vectors is very limited in Aligarh. The environmental and climatological situations permit the continual breeding of vectors in permanent breeding sites. This study was designed with the aim to screen all the anophelines species and possible malaria vectors in three different localities of Aligarh. Anopheles mosquitoes were collected from three different localities (Fort, Jalali and Tappal) during peak malaria transmission season (July to November) by using mouth aspirator and CDC light traps. Enzyme-linked immunosorbent assay (ELISA) was done to detect Plasmodium falciparum, Plasmodium vivax-210 and P. vivax-247 circumsporozoite proteins (CSP) from the collected female species. A total of 794 female anopheline mosquitoes belonging to 7 species were collected by different methods. Circumsporozoite protein–enzyme-linked immunosorbent assay was performed with 780 anopheline mosquitoes out of which 13 mosquitoes were positive in CSP–ELISA. Thus, the overall infection rate was 1.66% (13/780). Four (0.51%) mosquitoes belonging to three species were positive for P. falciparum, 7 (0.89%) mosquitoes belonging to three species were positive for VK 210 and 2 (0.25%) mosquitoes belonging to Anopheles culicifacies and Anopheles stephensi species were positive for VK 247. No mixed infection was found in this study. According to species, the highest infection rate was observed in An. culicifacies (7/288, 2.43%) followed by An. stephensi (2.40%) and Anopheles annularis (1.98%). An. culicifacies and An. stephensi were previously incriminated as malaria vectors in Aligarh. There was, however, no previous report in favor of infections in An. annularis in Aligarh. The on-going Malaria Control Program in India needs up to date information on malaria vectors. A major challenge is the lack of knowledge about vectors and their role in malaria transmission. Findings of this study suggested that in the absence of major malaria vectors there is a possibility that other Anopheles species may have been playing a role in malaria transmission in Aligarh.

Molecular characterization, biological forms and sporozoite rate of Anopheles stephensi in southern Iran

OBJECTIVE

To identify the biological forms, sporozoite rate and molecular characterization of the Anopheles stephensi (An. stephensi) in Hormozgan and Sistan-Baluchistan provinces, the most important malarious areas in Iran.

METHODS

Wild live An. stephensi samples were collected from different malarious areas in southern Iran. The biological forms were identified based on number of egg-ridges. Molecular characterization of biological forms was verified by analysis of the mitochondrial cytochrome oxidase subunit I and II (mtDNA-COI/COII). The Plasmodium infection was examined in the wild female specimens by species-specific nested-PCR method.

RESULTS

Results showed that all three biological forms including mysorensis, intermediate and type are present in the study areas. Molecular investigations revealed no genetic variation between mtDNA COI/COII sequences of the biological forms and no Plasmodium parasites was detected in the collected mosquito samples.

CONCLUSIONS

Presence of three biological forms with identical sequences showed that the known biological forms belong to a single taxon and the various vectorial capacities reported for these forms are more likely corresponded to other epidemiological factors than to the morphotype of the populations. Lack of malaria parasite infection in An. stephensi, the most important vector of malaria, may be partly due to the success and achievement of ongoing active malaria control program in the region.

Characterizing microclimate in urban malaria transmission settings: a case study from Chennai, India

Background

Environmental temperature is an important driver of malaria transmission dynamics. Both the parasite and vector are sensitive to mean ambient temperatures and daily temperature variation. To understand transmission ecology, therefore, it is important to determine the range of microclimatic temperatures experienced by malaria vectors in the field.

Methods

A pilot study was conducted in the Indian city of Chennai to determine the temperature variation in urban microclimates and characterize the thermal ecology of the local transmission setting. Temperatures were measured in a range of probable indoor and outdoor resting habitats of Anopheles stephensi in two urban slum malaria sites. Mean temperatures and daily temperature fluctuations in local transmission sites were compared with standard temperature measures from the local weather station. The biological implications of the different temperatures were explored using temperature-dependent parasite development models to provide estimates of the extrinsic incubation period (EIP) of Plasmodium vivax and Plasmodium falciparum.

Results

Mean daily temperatures within the urban transmission sites were generally warmer than those recorded at the local weather station. The main reason was that night-time temperatures were higher (and hence diurnal temperature ranges smaller) in the urban settings. Mean temperatures and temperature variation also differed between specific resting sites within the transmission environments. Most differences were of the order of 1-3°C but were sufficient to lead to important variation in predicted EIPs and hence, variation in estimates of transmission intensity.

Conclusions

Standard estimates of environmental temperature derived from local weather stations do not necessarily provide realistic measures of temperatures within actual transmission environments. Even the small differences in mean temperatures or diurnal temperature ranges reported in this study can lead to large variations in key mosquito and/or parasite life history traits that determine transmission intensity. Greater effort should be directed at quantifying adult mosquito resting behaviour and determining the temperatures actually experienced by mosquitoes and parasites in local transmission environments. In the absence of such highly resolved data, the approach used in the current study provides a framework for improved thermal characterization of transmission settings.

Insecticidal and genotoxic activity of Psoralea corylifolia Linn. (Fabaceae) against Culex quinquefasciatus Say, 1823

BACKGROUND

Indiscriminate use of synthetic insecticides to eradicate mosquitoes has caused physiological resistance. Plants provide a reservoir of biochemical compounds; among these compounds some have inhibitory effect on mosquitoes. In the present study the larvicidal, adulticidal and genotoxic activity of essential oil of Psoralea corylifolia Linn. against Culex quinquefasciatus Say was explored.

METHODS

Essential oil was isolated from the seeds of P. corylifolia Linn. Larvicidal and adulticidal bioassay of Cx. quinquefasciatus was carried out by WHO method. Genotoxic activity of samples was determined by comet assay. Identification of different compounds was carried out by gas chromatography- mass spectrometry analysis.

RESULTS

LC50 and LC90 values of essential oil were 63.38±6.30 and 99.02±16.63 ppm, respectively against Cx. quinquefasciatus larvae. The LD50 and LD90 values were 0.057±0.007 and 0.109±0.014 mg/cm2 respectively against adult Cx. quinquefasciatus,. Genotoxicity of adults was determined at 0.034 and 0.069 mg/cm2. The mean comet tail length was 6.2548±0.754 μm and 8.47±0.931 μm and the respective DNA damage was significant i.e. 6.713% and 8.864% in comparison to controls. GCMS analysis of essential oil revealed 20 compounds. The major eight compounds were caryophyllene oxide (40.79%), phenol,4-(3,7-dimethyl-3-ethenylocta-1,6-dienyl) (20.78%), caryophyllene (17.84%), α-humulene (2.15%), (+)- aromadendrene (1.57%), naphthalene, 1,2,3,4-tetra hydro-1,6-dimethyle-4-(1-methyl)-, (1S-cis) (1.53%), trans- caryophyllene (0.75%), and methyl hexadecanoate (0.67%).

CONCLUSION

Essential oil obtained from the seeds of P. corylifolia showed potent toxicity against larvae and adult Cx. quinquefasciatus. The present work revealed that the essential oil of P. corylifolia could be used as environmentally sound larvicidal and adulticidal agent for mosquito control.

Malaria in South Asia: prevalence and control

The "Malaria Evolution in South Asia" (MESA) program project is an International Center of Excellence for Malaria Research (ICEMR) sponsored by the US National Institutes of Health. This US-India collaborative program will study the origin of genetic diversity of malaria parasites and their selection on the Indian subcontinent. This knowledge should contribute to a better understanding of unexpected disease outbreaks and unpredictable disease presentations from Plasmodium falciparum and Plasmodium vivax infections. In this first of two reviews, we highlight malaria prevalence in India. In particular, we draw attention to variations in distribution of different human-parasites and different vectors, variation in drug resistance traits, and multiple forms of clinical presentations. Uneven malaria severity in India is often attributed to large discrepancies in health care accessibility as well as human migrations within the country and across neighboring borders. Poor access to health care goes hand in hand with poor reporting from some of the same areas, combining to possibly distort disease prevalence and death from malaria in some parts of India. Corrections are underway in the form of increased resources for disease control, greater engagement of village-level health workers for early diagnosis and treatment, and possibly new public-private partnerships activities accompanying traditional national malaria control programs in the most severely affected areas. A second accompanying review raises the possibility that, beyond uneven health care, evolutionary pressures may alter malaria parasites in ways that contribute to severe disease in India, particularly in the NE corridor of India bordering Myanmar Narayanasamy et al., 2012.