Mosquito-borne diseases in India over the past 50 years and their Global Public Health Implications: A Systematic Review

Mosquito-borne diseases (MBDs) pose a significant public health concern globally, and India, with its unique eco-sociodemographic characteristics, is particularly vulnerable to these diseases. This comprehensive review aims to provide an in-depth overview of MBDs in India, emphasizing their impact and potential implications for global health. The article explores distribution, epidemiology, control or elimination, and economic burden of the prevalent diseases such as malaria, dengue, chikungunya, Japanese encephalitis, and lymphatic filariasis, which collectively contribute to millions of cases annually. It sheds light on their profound effects on morbidity, mortality, and socioeconomic burdens and the potential for international transmission through travel and trade. The challenges and perspectives associated with controlling mosquito populations are highlighted, underscoring the importance of effective public health communication for prevention and early detection. The potential for these diseases to spread beyond national borders is recognized, necessitating a holistic approach to address the challenge. A comprehensive literature search was conducted, covering the past five decades (1972-2022), utilizing databases such as Web of Science, PubMed, and Google Scholar, in addition to in-person library consultations. The literature review analyzed 4,082 articles initially identified through various databases. After screening and eligibility assessment, 252 articles were included for analysis. The review focused on malaria, dengue, chikungunya, Japanese encephalitis, and lymphatic filariasis. The included studies focused on MBDs occurrence in India, while those conducted outside India, lacking statistical analysis, or published before 1970 were excluded. This review provides valuable insights into the status of MBDs in India and underscores the need for concerted efforts to combat these diseases on both national and global scales through consilience.

The impact of transgenesis on mosquito fitness: A review

Transgenic mosquitoes developed by genetic manipulation, offer a promising strategy for the sustainable and effective control of mosquito-borne diseases. This strategy relies on the mass release of transgenic mosquitoes into the wild, where their transgene is expected to persist in the natural environment, either permanently or transiently, within the mosquito population. In such circumstances, the fitness of transgenic mosquitoes is an important factor in determining their survival in the wild. The impact of transgene expression, insertional mutagenesis, inbreeding depression related to laboratory adaptation, and the hitchhiking effect involved in developing homozygous mosquito lines can all have an effect on the fitness of transgenic mosquitoes. Therefore, real-time estimation of transgene-associated fitness cost is imperative for modeling and planning transgenic mosquito release programs. This can be achieved by directly comparing fitness parameters in individuals homozygous or hemizygous for the transgene and their wild-type counterparts, or by cage invasion experiments to monitor the frequency of the transgenic allele over multiple generations. Recent advancements such as site-specific integration systems and gene drives, provide platforms to address fitness issues in transgenic mosquitoes. More research on the fitness of transgenic individuals is required to develop transgenic mosquitoes with a low fitness cost.

Understanding the mechanism of Chikungunya virus vector competence in three species of mosquitoes

Chikungunya virus (CHIKV) is primarily transmitted by Aedes spp. mosquitoes. The present study investigated vector competence for CHIKV in Aedes aegypti and Aedes albopictus mosquitoes found in Madurai, South India. The role of receptor proteins on midguts contributing to permissiveness of CHIKV to Aedes spp. mosquitoes was also undertaken. Mosquitoes were orally infected with CHIKV DRDE-06. Infection of midguts and dissemination to heads was confirmed by immunofluorescence assay at different time points. A plaque assay was performed from mosquito homogenates at different time points to study CHIKV replication. Presence of putative CHIKV receptor proteins on mosquito midgut epithelial cells was detected by virus overlay protein binding assay (VOPBA). The identity of these proteins was established using mass spectrometry. CHIKV infection of Ae. aegypti and Ae. albopictus midguts and dissemination to heads was observed to be similar. A plaque assay performed with infected mosquito homogenates revealed that CHIKV replication dynamics was similar in Aedes sp. mosquitoes until 28 days post infection. VOPBA performed with mosquito midgut membrane proteins revealed that prohibitin could serve as a putative CHIKV receptor on Aedes mosquito midguts, whereas an absence of CHIKV binding protein/s on Culex quinquefasciatus midguts can partially explain the non-permissiveness of these mosquitoes to infection.

Biological nanopesticides: a greener approach towards the mosquito vector control

Mosquitoes, being a vector for some potentially dreadful diseases, pose a considerable threat to people all around the world. The control over the growth and propagation of mosquitoes comprises conventional pesticides, insect growth regulators and other microbial control agents. However, the usage of these common chemicals and conventional pesticides eventually has a negative impact on human health as well as the environment, which therefore becomes a major concern. The lacuna allows nanotechnology to come into action and exploit nanopesticides. Nanopesticides are majorly divided into two categories-synthetic and biological. Several nanoformulations serve as a promising nanopesticide viz. nanoparticles, e.g. biologically synthesised nanoparticles through plant extracts, nanoemulsions prepared using the essential oils like neem oil and citronella oil and nanoemulsion of conventional pesticides like pyrethroids. These green approaches of synthesising nanopesticides make use of non-toxic and biologically derived compounds and hence are eco-friendly with a better target specificity. Even though there are numerous evidences to show the effectiveness of these nanopesticides, very few efforts have been made to study the possible non-target effects on other organisms prevalent in the aquatic ecosystem. This study focuses on the role of these nanopesticides towards the vector control and its eco-safe property against the other non-target species.

Environmentally benign nanometric neem-laced urea emulsion for controlling mosquito population in environment

The increasing risk of vector-borne diseases and the environmental pollution in the day-to-day life due to the usage of the conventional pesticides makes the role of nanotechnology to come into the action. The current study deals with one of the applications of nanotechnology through the formulation of neem urea nanoemulsion (NUNE). NUNE was formulated using neem oil, Tween 20, and urea using the microfluidization method. Prior to the development of nanoemulsion, the ratio of oil/surfactant/urea was optimized using the response surface modeling method. The mean droplet size of the nanoemulsion was found to be 19.3 ± 1.34 nm. The nanoemulsion was found to be stable for the period of 4 days in the field conditions which aids to its mosquitocidal activity. The nanoemulsion exhibited a potent ovicidal and larvicidal activity against A. aegypti and C. tritaeniorhynchus vectors. This result was corroborated with the histopathological analysis of the NUNE-treated larvae. Further, the effect of NUNE on the biochemical profile of the target host was assessed and was found to be efficacious compared to the bulk counterpart. The nanoemulsion was then checked for its biosafety towards the non-target species like plant beneficial bacterium (E. ludwigii), and phytotoxicity was assessed towards the paddy plant (O. sativa). Nanometric emulsion at the concentration used for the mosquitocidal application was found to be potentially safe towards the environment. Therefore, the nanometric neem-laced urea emulsion tends to be an efficient mosquito control agent with an environmentally benign property.

Stability of nano-sized permethrin in its colloidal state and its effect on the physiological and biochemical profile of Culex tritaeniorhynchus larvae

The occurrence of pesticidal pollution in the environment and the resistance in the mosquito species makes an urge for the safer and an effective pesticide. Permethrin, a poorly water-soluble pyrethroid pesticide, was formulated into a hydrodispersible nanopowder through rapid solvent evaporation of pesticide-loaded oil in water microemulsion. Stability studies confirmed that the nanopermethrin dispersion was stable in paddy field water for 5 days with the mean particle sizes of 175.3 ± 0.75 nm and zeta potential of -30.6 ± 0.62 mV. The instability rate of the nanopermethrin particles was greater in alkaline (pH 10) medium when compared with the neutral (pH 7) and acidic (pH 4) dispersion medium. The colloidal dispersion at 45°C was found to be less stable compared with the dispersions at 25 and 5°C. The 12- and 24-h lethal indices (LC50) for nanopermethrin were found to be 0.057 and 0.014 mg l-1, respectively. These results were corroborative with the severity of damages observed in the mosquito larvae manifested in epithelial cells and the evacuation of the midgut contents. Further, the results were substantiated by the decrease in cellular biomolecules and biomarker enzyme activity in nanopermethrin treated larvae when compared to bulk and control treatment.

Stability assessment of hydro dispersive nanometric permethrin and its biosafety study towards the beneficial bacterial isolate from paddy rhizome

Nanopesticides such as nanopermethrin can serve as an alternative to conventional pesticides causing eco-toxicity. The nanoformulation of this pyrethroid pesticide was carried out by solvent evaporation of pesticide-loaded microemulsion. The Z average for the nanopermethrin dispersion in paddy field water was found to be 169.2 ± 0.75 nm with a polydispersity index of 0.371 that exhibits uniform dispersion. Further, the nanopermethrin (NP) dispersion exhibited an effective stability in the paddy field water for a duration of 48 h with a Z average of 177.3 ± 1.2 nm and a zeta potential of -30.7 ± 0.9 mV. The LC₅₀ of the nanopermethrin against Culex tritaeniorhynchus in the field condition was found to be 0.051 μg/mL. In addition to the stability assessment, the biosafety of the nanopermethrin was commenced on the beneficial bacterial isolate Enterobacter ludwigii (VITSPR1) considered as plant growth-promoting rhizobacteria. The toxic effect of nanopesticide was compared to its bulk counterpart, i.e. bulk permethrin (BP) at a concentration of 100 µg/mL, and the nanopesticide was found to be potentially safe. The results of biomarker enzymatic assays (lipid peroxidase, glutathione reductase, lactate dehydrogenase) displayed insignificant (p < 0.05) toxicity of NP towards the bacterial cells compared to BP. The live-dead cell staining and SEM analysis illustrated negligible toxicity of NP towards the bacteria. The non-toxic behaviour of the NP towards the non-target species was studied which displayed the eco-safe property of NP.

Seasonal abundance & role of predominant Japanese encephalitis vectors Culex tritaeniorhynchus & Cx. gelidus Theobald in Cuddalore district, Tamil Nadu

Background & objectives:

Japanese encephalitis (JE) is the leading cause of viral encephalitis in Asia. The first major JE outbreak occurred in 1978 and since 1981 several outbreaks had been reported in the Cuddalore district (erstwhile South Arcot), Tamil Nadu, India. Entomological monitoring was carried out during January 2010 - March 2013, to determine the seasonal abundance and transmission dynamics of the vectors of JE virus, with emphasis on the role of Culex tritaeniorhynchus and Cx. gelidus.

Methods:

Mosquito collections were carried out fortnightly during dusk hours in three villages viz. Soundara Solapuram, Pennadam, Erappavur of Cuddalore district. Mosquitoes were collected during dusk for a period of one hour in and around the cattle sheds using oral aspirator and torch light. The collected mosquitoes were later identified and pooled to detect JE virus (JEV) infection by enzyme linked immunosorbent assay (ELISA).

Results:

A total of 46,343 mosquitoes comprising of 25 species and six genera were collected. Species composition included viz, Cx. tritaeniorhynchus (46.26%), Cx. gelidus (43.12%) and other species (10.62%). A total of 17,678 specimens (403 pools) of Cx. gelidus and 14,358 specimens (309 pools) of Cx. tritaeniorhynchus were tested, of which 12 pools of Cx. gelidus and 14 pools of Cx. tritaeniorhynchus were positive for JE virus antigen. The climatic factors were negatively correlated with minimum infection rate (MIR) for both the species, except mean temperature (P<0.05) for Cx. gelidus.

Interpretation & conclusions:

High abundance of Cx. tritaeniorhynchus and Cx. gelidus was observed compared to other mosquito species in the study area. Detection of JEV antigen in the two species confirmed the maintenance of virus. Appropriate vector control measures need to be taken to reduce the vector abundance.

Impact on prevalence of intestinal helminth infection in school children administered with seven annual rounds of diethyl carbamazine (DEC) with albendazole

BACKGROUND & OBJECTIVES

One third of the world's population is infected with one or more of the most common soil-transmitted helminths (STH). Albendazole (ALB) is being administered with diethyl carbamazine (DEC) in filariasis endemic areas to eliminate lymphatic filariasis (LF) and helminth infections. In this study, the cumulative impact of seven annual rounds of mass drug administrations (MDA) of DEC and ALB on STH infection in school children in selected villages in southern India was determined.

METHODS

During 2001-2010, seven MDAs were implemented by the Tamil Nadu s0 tate h0 ealth d0 epartment, India. LF and STH infections were monitored in school children from 18 villages of the two treatment arms (viz, DEC alone and DEC+ALB). Kato-Katz cellophane quantitative thick smear technique was employed to estimate STH infections at three weeks, six months and one year post MDA.

RESULTS

Prior to treatment, an overall STH prevalence was 60 per cent. After each MDA, infection markedly reduced at three weeks post-treatment in both the arms. The prevalence increased at six months period, which was maintained up to one year. After seven rounds of MDA, the infection reduced from 60.44 to 12.48 per cent in DEC+ALB arm; while the reduction was negligible in DEC alone arm (58.77 to 52.70%).

INTERPRETATION & CONCLUSIONS

Seven rounds of MDA with DEC+ALB reduced the infection load significantly, and further sustained low level of infection for 10 years. However, complete parasite elimination could not be achieved. To curtail STH infection in the community, MDA should be regularized and environmental sanitation measures need to be improved by effective community-based campaigns.

A Preliminary Study to Forecast Japanese Encephalitis Vector Abundance in Paddy Growing Area, with the Aid of Radar Satellite Images

Vector mosquitoes of Japanese encephalitis (JE) breed mostly in rice fields, and human cases occur scattered over extended rural rice-growing areas. From this, one may surmise an ecological connection with the irrigation facilities and paddy cultivation. Furthermore, it has been hypothesized that a particular stage of paddy growth is a premonitory sign that can lead to a markedly increased population of the vector mosquitoes. The present study aimed to forecast the vector abundance by monitoring the paddy growth using remote sensing and geographical information systems. The abundance of the JE vector Culex tritaeniorhynchus peaked when the paddy crop was at its heading stage and dipped when the crop reached the maturing stage. A significant positive correlation was observed between paddy growth and adult density (r = 0.73, p < 0.008). The sigma naught values (σ0) derived from satellite images of paddy fields ranged from -18.3 (during transplantation stage) to approximately -10 (during the noncultivation period). A significant positive correlation was observed between σ0 and paddy growth stages (r = 0.87, p < 0.05) and adult vector density (r = 0.74, p = 0.04). The σ0 value observed during the vegetative and flowering stages of paddy growth ranged from -17.6 to -17.16, at which period the vector density started building up. This could be the spectral signature that denotes the "risk," following which a high vector abundance is expected during heading stage of the paddy.

Dengue vectors prevalence and the related risk factors involved in the transmission of dengue in Thiruvananthapuram district, Kerala, South India

BACKGROUND & OBJECTIVES

A longitudinal, entomological and virological study was conducted from 2007 to 2010 in four dengue fever affected areas of Thiruvananthapuram district, Kerala to understand the risk factors involved in the dengue transmission.

METHODS

Aedes surveys were carried out seasonally in the selected localities both indoors and peridomestic sites. Water holding containers were sampled for the presence of immature. Outdoor and indoor resting/landing mosquitoes were collected. Blood meal identification was performed by gel diffusion test and viral assay using the ELISA test.

RESULTS

The species found were Aedes (Stegomyia) aegypti (Linn.), Ae. (Stegomyia) albopictus (Skuse) and Ae. (Stegomyia) vittatus (Bigot). Aedes aegypti and Ae. albopictus immature stages were also found during the study period. Aedes aegypti was the only prevalent species in the water-starved Vizhinjam, a rural coastal area with breteau index (BI) ranging from 40 to 271. Aedes albopictus was recorded in rest of the three surveyed localities—two urban and one rural ghat areas of Thiruvananthapuram district.

INTERPRETATION & CONCLUSION

The vector control measures should be focused mainly on source reduction of water storage containers present in both outdoor (Ae. albopictus and Ae. vittatus) and indoor (Ae. aegypti). To achieve effective vector management, a public health response beyond routine larviciding or focal spraying is essential throughout the year.

Economic and disease burden of dengue illness in India

Between 2006 and 2012 India reported an annual average of 20,474 dengue cases. Although dengue has been notifiable since 1996, regional comparisons suggest that reported numbers substantially underrepresent the full impact of the disease. Adjustment for underreporting from a case study in Madurai district and an expert Delphi panel yielded an annual average of 5,778,406 clinically diagnosed dengue cases between 2006 and 2012, or 282 times the reported number per year. The total direct annual medical cost was US$548 million. Ambulatory settings treated 67% of cases representing 18% of costs, whereas 33% of cases were hospitalized, comprising 82% of costs. Eighty percent of expenditures went to private facilities. Including non-medical and indirect costs based on other dengue-endemic countries raises the economic cost to $1.11 billion, or $0.88 per capita. The economic and disease burden of dengue in India is substantially more than captured by officially reported cases, and increased control measures merit serious consideration.

Decline in lymphatic filariasis transmission with annual mass drug administration using DEC with and without albendazole over a 10year period in India

The National Programme for the Elimination of Lymphatic Filariasis is underway in the endemic districts of Tamil Nadu State, South India, since 2001. Annual mass drug administration (MDA) was carried out by the state health department to all eligible individuals. The impact of MDAs on transmission parameters was evaluated in 2 revenue blocks, viz, one with DEC alone and the other with a combination of albendazole. After 10 years with 6 annual MDAs, the transmission indices reached low levels in both treatment arms, but still persisted. However, the DEC alone arm showed higher transmission rates, compared to the DEC+ALB arm. Few villages which demonstrated persistent transmission need to be targeted with an additional control measure viz, vector control, to achieve LF elimination. It is evident from the 10 year period of the study that inclusion of albendazole along with DEC has significantly reduced the transmission indices to almost nil level, as compared to DEC alone.

Nanoemulsion of eucalyptus oil and its larvicidal activity against Culex quinquefasciatus

Filariasis is a mosquito-borne disease that causes lymphedema and the main vector is Culex quinquefasciatus. A simple measure was taken to eradicate the vector using nanoemulsion. Eucalyptus oil nanoemulsion was formulated in various ratios comprising of eucalyptus oil, tween 80 and water by ultrasonication. The stability of nanoemulsion was observed over a period of time and 1:2 ratios of eucalyptus oil (6%) and surfactant (12%) was found to be stable. The formulated eucalyptus oil nanoemulsion was characterized by transmission electron microscopy and dynamic light scattering. The nanoemulsion droplets were found to have a Z-average diameter of 9.4 nm and were spherical in shape. The larvicidal activity of eucalyptus oil nanoemulsion and bulk emulsion was tested and compared. Our nanoemulsion showed higher activity when compared to bulk emulsion. The histopathology of larvae-treated and untreated nanoemulsion was analyzed. Furthermore, biochemical assays were carried out to examine the effect of nanoemulsion on biochemical characteristics of larvae. The treated larval homogenate showed decrease in total protein content and a significant reduction in the levels of acetylcholinesterase. The levels of acid and alkaline phosphatase also showed reduction as compared to control larval homogenate.

Persistence of lymphatic filarial infection in the paediatric population of rural community, after six rounds of annual mass drug administrations

Under the Global Programme to Eliminate Lymphatic Filariasis (LF), mass drug administration (MDA) is being implemented in Tamil Nadu, south India, by the State health machinery. The impact of six annual rounds of MDA using diethylcarbamazine (DEC) with and without albendazole (ALB) on filarial infection (microfilaraemia prevalence-MFP; antigenaemia prevalence-AGP) in paediatric population of 2-9 years was determined in two revenue blocks, with a population of 321 000. After each MDA, 300-400 children were screened for filarial infection. After six MDAs, an overall MFP reduction of 84.67% and 57.95% was observed in DEC+ALB and DEC alone arms, respectively. Corresponding AGP reductions were 72.88% (p < 0.001) and 41.51% (p = 0.023). Observation of microfilaraemic children after six MDAs (0.32% in DEC+ALB; 0.75% in DEC alone), necessitates the need for supplementary control strategies (viz., vector control), in order to achieve the goal of LF elimination.

Dengue NS1 and prM antibodies increase the sensitivity of acute dengue diagnosis test and differentiate from Japanese encephalitis infection

Accurate and early diagnosis of dengue infection is essential for dengue case management. In outbreak conditions, it is essential to include two different tests to diagnose dengue and the choice depends on the number of days after the onset of illness in which the sample is collected. During the laboratory diagnosis of dengue in late acute and convalescent phase by MAC-ELISA, it is necessary to rule out possible cross reactions of closely related flavivirus, such as Japanese encephalitis virus which is commonly co-circulating. In the present investigation, the usefulness of dengue virus NS1 and prM antibodies in diagnosing and differentiating dengue from Japanese encephalitis infection was assessed using samples collected during out-breaks. It was shown here that, detection of antibodies against dengue NS1 and prM proteins increases the sensitivity of dengue diagnosis until 15days. Moreover, detection of antibodies against both proteins was able to differentiate dengue from Japanese encephalitis infection.

Community-based control of Aedes aegypti by adoption of eco-health methods in Chennai City, India

Background

Dengue is highly endemic in Chennai city, South India, in spite of continuous vector control efforts. This intervention study was aimed at establishing the efficacy as well as the favouring and limiting factors relating to a community-based environmental intervention package to control the dengue vector Aedes aegypti.

Methods

A cluster randomized controlled trial was designed to measure the outcome of a new vector control package and process analysis; different data collection tools were used to determine the performance. Ten randomly selected intervention clusters (neighbourhoods with 100 houses each) were paired with ten control clusters on the basis of ecological/entomological indices and sociological parameters collected during baseline studies. In the intervention clusters, Aedes control was carried out using a community-based environmental management approach like provision of water container covers through community actors, clean-up campaigns, and dissemination of dengue information through schoolchildren. The main outcome measure was reduction in pupal indices (pupae per person index), used as a proxy measure of adult vectors, in the intervention clusters compared to the control clusters.

Results

At baseline, almost half the respondents did not know that dengue is serious but preventable, or that it is transmitted by mosquitoes. The stakeholder analysis showed that dengue vector control is carried out by vertically structured programmes of national, state, and local administrative bodies through fogging and larval control with temephos, without any involvement of community-based organizations, and that vector control efforts were conducted in an isolated and irregular way. The most productive container types for Aedes pupae were cement tanks, drums, and discarded containers. All ten intervention clusters with a total of 1000 houses and 4639 inhabitants received the intervention while the ten control clusters with a total of 1000 houses and 4439 inhabitants received only the routine government services and some of the information education and communication project materials. The follow-up studies showed that there was a substantial increase in dengue understanding in the intervention group with only minor knowledge changes in the control group. Community involvement and the partnership among stakeholders (particularly women’s self-help groups) worked well. After 10 months of intervention, the pupae per person index was significantly reduced to 0.004 pupae per person from 1.075 (P = 0.020) in the intervention clusters compared to control clusters. There were also significant reductions in the Stegomyia indices: the house index was reduced to 4.2%, the container index to 1.05%, and the Breteau index to 4.3 from the baseline values of 19.6, 8.91, and 30.8 in the intervention arm.

Conclusion

A community-based approach together with other stakeholders that promoted interventions to prevent dengue vector breeding led to a substantial reduction in dengue vector density.

Estimating dengue vector abundance in the wet and dry season: implications for targeted vector control in urban and peri-urban Asia

Background

Research has shown that the classical Stegomyia indices (or “larval indices”) of the dengue vector Aedes aegypti reflect the absence or presence of the vector but do not provide accurate measures of adult mosquito density. In contrast, pupal indices as collected in pupal productivity surveys are a much better proxy indicator for adult vector abundance. However, it is unknown when it is most optimal to conduct pupal productivity surveys, in the wet or in the dry season or in both, to inform control services about the most productive water container types and if this pattern varies among different ecological settings.

Methods

A multi-country study in randomly selected twelve to twenty urban and peri-urban neighborhoods (“clusters”) of six Asian countries, in which all water holding containers were examined for larvae and pupae of Aedes aegypti during the dry season and the wet season and their productivity was characterized by water container types. In addition, meteorological data and information on reported dengue cases were collected.

Findings

The study reconfirmed the association between rainfall and dengue cases (“dengue season”) and underlined the importance of determining through pupal productivity surveys the “most productive containers types”, responsible for the majority (>70%) of adult dengue vectors. The variety of productive container types was greater during the wet than during the dry season, but included practically all container types productive in the dry season. Container types producing pupae were usually different from those infested by larvae indicating that containers with larval infestations do not necessarily foster pupal development and thus the production of adult Aedes mosquitoes.

Conclusion

Pupal productivity surveys conducted during the wet season will identify almost all of the most productive container types for both the dry and wet seasons and will therefore facilitate cost-effective targeted interventions.

Identification of structural motifs in the E2 glycoprotein of Chikungunya involved in virus-host interaction

Chikungunya fever is one of the reemerging vector-borne diseases. It has become a major global health problem especially in the developing countries. There are no vaccines or specific antiviral drugs available to date. This study reports small molecule inhibitors of envelope glycoprotein 2 (E2 glycoprotein) which are predicted based on Chikungunya virus-host interactions. E2 glycoprotein of Chikungunya virus interacts at 216 residue of the host receptor protein which plays a vital role in initiating infection. Understanding the structural aspects of E2 glycoprotein is crucial to develop specific inhibitors to prevent the virus binding from host receptors. In silico method was adopted to predict the sequence motifs of envelope protein, as the method like yeast two hybrid system is laborious, time consuming, and costly. The E2 glycoprotein structure of the Indian isolate was modeled using two templates (2XFC and 3JOC) and then validated. The class III PDZ domain binding motif was found to be identified at 213-216 amino acids. The corresponding peptide structures which recognize the PDZ domain binding motif were identified by the literature search and were used for generating five point pharmacophore model (ADDDR) containing acceptor, donor and aromatic ring features. Databases such as Asinex, TosLab and Maybridge were searched for the matches for the predicted pharmacophore model. Two compounds were identified as lead molecules as their glide score is > 5 kcal/mol. Since the pharmacophore model is developed based on Chikungunya virus-host interaction, it can be used for designing promising antiviral lead compounds for the treatment of Chikungunya fever.An animated Interactive 3D Complement (I3DC) is available in Proteopedia at http://proteopedia.org/w/Journal:JBSD:21.

Wolbachia endobacteria in a natural population of Culex quinquefasciatus from filariasis endemic villages of south India and its phylogenetic implication

Understanding Wolbachia mosquito interactions have been recognized as an important concept to develop novel vector control strategies. The prevalence of Wolbachia endobacteria in a natural population of the filariasis vector Culex quinquefasciatus was determined by the polymerase chain reaction method. Earlier workers had estimated the infection rates of Wolbachia with only one or very few individuals per species. In our study large number of specimens were assayed, and a total of 750 adult Culex quinquefasciatus mosquitoes were collected from three south Indian villages of Tirukoilur and Mugaiyur blocks, monthly for a period of five months (December 2006 to April 2007) and screened for the presence of Wolbachia. The percentage prevalence in adult males ranged from 88% to 96%; while in females from 84% to 100%. An overall prevalence of 91.2% was observed. There was no significant difference observed in the proportion of mosquitoes positive for Wolbachia between males and females, and also between different months of the survey; except during the month of February '07. The wsp gene sequence of the Wolbachia strain of Cx. quinquefasciatus detected was BLAST analysed and showed 99% sequence similarity with Wolbachia sp. of Culex pipiens isolated from different geographical regions. Phylogenetic analysis based on wsp gene fragments showed that the present Wolbachia isolate was closely related with Wolbachia from Culex pipens pipiens, Niphotettix virescens (Order: Hemiptera) and Cnaphalocrosis medinalis (Order: Lepidoptera).

Insecticide susceptibility and resistance development in malathion selected Aedes albopictus (Skuse)

Aedes albopictus was bioassayed to determine resistance development to malathion (OP). Two methods were applied, including WHO larval bioassay to determine the susceptibility to lethal concentration (LC), and adult bioassay to determine lethal time (LT). Larvae from colonies that had undergone selection pressure with malathion to yield 50% mortality were further subjected to selection for subsequent 10 generations. Selection of Ae. albopictus with malathion could relatively induce a consistent resistance ratio of 1.0 throughout 10 generations. It was noted that Ae. albopictus larvae showed less susceptibility to malathion compared to adults. The susceptibility test of adult mosquitoes to diagnostic dosage of 5.0% malathion-impregnated paper showed a variety of susceptibility to malathion when compared to the susceptible strain. Bioassay results indicated that the LT50 values of malathion-selected Ae. albopictus ranged between 11.5 - 58.8 minutes for ten consecutive generations. Biochemical enzyme studies indicated that there was a significant difference (p < 0.05) in esterase level in malathion-selected mosquitoes compared to non-selected control. Electrophoretic patterns of non-specific esterases at different life stages in malathion-selected Ae. albopictus suggested that non-specific esterases do not play a role in resistance of malathion-selected Ae. albopictus.

Eco-bio-social determinants of dengue vector breeding: a multicountry study in urban and periurban Asia

OBJECTIVE

To study dengue vector breeding patterns under a variety of conditions in public and private spaces; to explore the ecological, biological and social (eco-bio-social) factors involved in vector breeding and viral transmission, and to define the main implications for vector control.

METHODS

In each of six Asian cities or periurban areas, a team randomly selected urban clusters for conducting standardized household surveys, neighbourhood background surveys and entomological surveys. They collected information on vector breeding sites, people's knowledge, attitudes and practices surrounding dengue, and the characteristics of the study areas. All premises were inspected; larval indices were used to quantify vector breeding sites, and pupal counts were used to identify productive water container types and as a proxy measure for adult vector abundance.

FINDINGS

The most productive vector breeding sites were outdoor water containers, particularly if uncovered, beneath shrubbery and unused for at least one week. Peridomestic and intradomestic areas were much more important for pupal production than commercial and public spaces other than schools and religious facilities. A complex but non-significant association was found between water supply and pupal counts, and lack of waste disposal services was associated with higher vector abundance in only one site. Greater knowledge about dengue and its transmission was associated with lower mosquito breeding and production. Vector control measures (mainly larviciding in one site) substantially reduced larval and pupal counts and "pushed" mosquito breeding to alternative containers.

CONCLUSION

Vector breeding and the production of adult Aedes aegypti are influenced by a complex interplay of factors. Thus, to achieve effective vector management, a public health response beyond routine larviciding or focal spraying is essential.

Studies on community knowledge and behavior following a dengue epidemic in Chennai city, Tamil Nadu, India

In 2001, a major dengue outbreak was recorded in Chennai city, with 737 cases (90%) out of a total of 861 cases recorded from Tamil Nadu state. A KAP survey was carried out to assess the community knowledge, attitude and practice on dengue fever (DF), following the major dengue outbreak in 2001. A pre- tested, structured questionnaire was used for data collection. The multistage cluster sampling method was employed and 640 households (HHs) were surveyed. Among the total HHs surveyed, 34.5% of HHs were aware of dengue and only 3.3% of HHs knew that virus is the causative agent for DF. Majority of the HHs (86.5%) practiced water storage and only 3% of them stored water more than 5 days. No control measures were followed to avoid mosquito breeding in the water holding containers by majority of HHs (65%). Sixty percent of HHs did not know the biting behaviour of dengue vector mosquitoes. The survey results indicate that the community knowledge was very poor on dengue, its transmission, vector breeding sources, biting behavior and preventive measures. The lack of basic knowledge of the community on dengue epidemiology and vector bionomics would be also a major cause of increasing trend of dengue in this highly populated urban environment. There is an inevitable need to organize health education programmes about dengue disease to increase community knowledge and also to sensitize the community to participate in integrated vector control programme to resolve the dengue problem.

Temporal variation in the susceptibility of Culex tritaeniorhynchus (Diptera: Culicidae) to Japanese encephalitis virus in an endemic area of Tamil Nadu, South India

The study area, Cuddalore, is one of the endemic districts for Japanese encephalitis (JE) in southern India and there is a strong seasonality in JE case incidence, as well as JE virus (JEV) infection in the principal vector Culex (Culex) tritaeniorhynchus Giles. In a longitudinal 3-year study (July 2003 to June 2006), we determined the susceptibility of wild-caught female Cx. tritaeniorhynchus for JEV infection over several seasons from several villages. The susceptibility varied in all four seasons with the lowest value (4.82 geometric mean [GM]) in hot and wet seasons and highest (13.22 GM) in cool and wet seasons. Infection rate was significant between seasons (7.08-11.85 GM) and years (4.82-13.22 GM). Although the vector was abundant throughout the year, with an average per man-hour density ranging from 58 to 652, the JEV infection rates showed no correlation with vector abundance during different seasons in the index villages. The temporal and spatial changes in the competency of the vector appeared to influence the JEV infection rate in vector, which may at least partially explain the seasonality in JEV human cases in the study area.

Role of community empowerment in the elimination of lymphatic filariasis in south India

The World Health Assembly in 1997 has targeted the elimination of lymphatic filariasis (LF) by 2020, and in India the goal has been set for the year 2015 by annual single dose mass drug administration (MDA). The role of community empowerment in enhancing the drug compliance and bringing out the function of various methods used to disseminate the information on MDA to the villagers is focused. A longitudinal survey was carried out in nine villages in Tirukoilur block of Villupuram district, Tamil Nadu for filarial infection variables like microfilaraemia, antigenaemia, transmission indices before and after each MDA, to determine the drug impact. Prior to each MDA, health education campaigns with different approaches were carried out with community as the leading player. These IEC approaches were assessed after 4 MDAs for its perception in the community. After four rounds of MDA, there was a significant decline in the filarial infection variables. The microfilaraemia and antigenaemia declined by 59% and 67% respectively. The transmission indices lowered by 89% and 94% (in resting and landing catch of mosquitoes respectively). The decline in these variables, with a drug consumption rate of >80% was achieved due to the effective IEC campaigns prior to each MDA. After 4 MDAs almost 97% of the respondents were aware of lymphatic filariasis. The KAP survey in the rural villages revealed that the dissemination of MDA message through autorickshaw was the most effective, followed by school students' rally. Empowerment of community through the members of women self help groups and school students were observed to be integral to mass drug administration campaigns for the enhancement of drug compliance, thus leading to LF elimination.

Molecular identification of mosquito vectors using genomic DNA isolated from eggshells, larval and pupal exuvium

Correct and precise identification of mosquito vectors is important in many respects including development of vector control strategies. Conventional identification methods have limitations for sibling and closely related species of mosquitoes, stage and quality of the specimen used and this could be overcome by DNA-based identification methods using molecular markers such as nuclear ribosomal internal transcribed spacer (ITS) which do not demand intact or undamaged specimen. Genomic DNA is usually isolated from whole mosquito, legs, wings etc. Alternate sources for genomic DNA isolation such as eggshells, larval and pupal exuviae were explored in this study by amplifying the ITS markers. Standardization of genomic DNA extraction and ITS amplification were carried out with laboratory specimens. The same was applied to specimens collected from the field. The results show that PCR amenable genomic DNA could be isolated from fresh exuviae collected in the laboratory and not from older and/or field specimens. But exuviae of larvae and/or pupae collected in the field reared to adulthood in the laboratory yielded PCR amenable genomic DNA. The results also revealed that the ITS2 marker could very well differentiate Aedes aegypti and Aedes albopictus by producing amplicons of ~330 bp and ~520 bp, respectively. The genomic DNA from these alternate sources also supported the species-specific PCR to distinguish the Culex vishnui subgroup mosquitoes.

Longitudinal studies of Japanese encephalitis virus infection in vector mosquitoes in Kurnool district, Andhra Pradesh, South India

A 4-yr (2002-2006) entomological study was carried out in Kurnool district, Andhra Pradesh state, south India, to identify the mosquito vectors of Japanese encephalitis virus (family Flaviviridae, genus Flavivirus, JEV). In total, 37,139 female mosquitoes belonging five genera and 18 species resting on vegetation were collected in villages and periurban areas at dusk. Mosquito species composition and pattern of JEV infection in mosquitoes varied in periurban and rural areas. In periurban area, Culex gelidus Theobald was abundant, making up 49.7% of total catch followed by Culex tritaeniorhynchus Giles (44.5%). In rural area, Cx. tritaeniorhynchus was predominant, making up 78.9% of total catch followed by Culex quinquefasciatus Say (10.8%), Anopheles subpictus Grassi (7.1%), and Cx. gelidus (1.1%). In light trap collections, Cx. gelidus and Cx. tritaeniorhynchus predominated in periurban and rural areas, respectively. Of 50,145 mosquitoes screened JEV isolations were made only from Cx. gelidus and Cx. tritaeniorhynchus. Based on high abundance and frequent JEV isolation, Cx. tritaeniorhynchus was found to be the principal vector in both areas, whereas Cx. gelidus plays a secondary vector role in periurban areas only.

Larvicidal efficacy of various formulations of Bacillus sphaericus against the resistant strain of Culex quinquefasciatus (Diptera: Culicidae) from southern India

Use of Bacillus sphaericus Neide (Bs) as potential biolarvicide in developing countries is limited due to development of resistance by target mosquitoes. Efforts are taken to look for appropriate formulations or combination of Bs to prevent or delay resistance problem. Here, we report the efficacy of a formulated Bs product to kill Bs resistant Culex quinquefasciatus Say larvae. The laboratory reared resistance colony was maintained by subjecting selection pressure with Bs (2362) toxin. Bioassays were conducted with lyophilized, standard formulated and Bs formulated by us (all belong to strain 2362, serotype H5a5b) against Bs resistant and susceptible colonies. The Bs resistant larvae showed a high level of resistance against lyophilized toxin with resistance ratio (RR) of 8375.2, 1055.6 and 11422.3 folds at LC(50), LC(90) and LC(95) levels, respectively, when compared with Bs susceptible larvae. With formulation of standard powder, the RR between Bs resistant and susceptible larvae were 1.01, 1.13 and 1.19 folds only at LC(50), LC(90) and LC(95) levels, respectively. This observation was comparable with our formulation prepared by a ground mixture of lyophilized Bs and a placebo (plaster of Paris). It is evident from our study, that the placebo present in our Bs 2362 formulation was responsible for increasing the efficacy of Bs lyophilized toxin against resistant larvae. The putative mechanism behind this toxicity phenomenon remains to be investigated to evolve new mosquito control strategies. A cross resistance to indigenous strain of Bs B42 (H5a5b) against Bs resistant larvae was also reported in this study.

A study on chikungunya outbreak during 2007 in Kerala, south India

BACKGROUND & OBJECTIVE

The first chikungunya outbreak occurred in Kerala during 2006 affecting 14 districts, followed by another during May 2007 affecting almost whole of the State. Four of the worst affected districts viz, Pathanamthitta, Idukki, Kottayam and Thrissur were surveyed during 2007 to understand the magnitude of the problem of chikungunya fever, particularly clinical signs and symptoms.

METHODS

A total of 1265 persons from 310 houses were surveyed door-to-door in 20 different localities representing four affected districts. The history and examination findings from 354 clinically diagnosed chikungunya cases were recorded. The symptoms recorded were fever, headache, myalgia, arthralgia, itch/rash, oedema, eye congestion, eye pain, oral ulcers, distaste, nausea, vomiting and haemorrhage.

RESULTS

The major symptoms were fever (100%), headache (97.5%), arthralgia (99.4%) and myalgia (99.4%). A significant difference was observed in oedema, distaste, nausea and headache among different age groups and these symptoms were reported to be lower (12.2-89.8%) in younger age group than in older age group (90.4-100%). No genderwise difference was observed for any of the symptoms. In clinically diagnosed chikungunya cases higher age group (>35 years) found with higher rate of severity with symptoms of oedema, distaste, nausea and headache when compared with lower age group (1-35 yr).

INTERPRETATION & CONCLUSION

Chikungunya invaded Kerala State for the first time in 2006 and continues to be a major vector borne disease in the State. The clinical symptoms in affected cases highlighted high fever, sever myalgia and prolonged arthralgia, with occasional history of skin itch/rash (petechiae).

Chikungunya virus isolated in Lakshadweep islands in the Indian Ocean: evidence of the Central/East African genotype

Virological investigation was carried out to determine the etiology of suspected Chikungunya fever among humans reported in the Lakshadweep islands in the Indian Ocean. Three out of 23 acute sera samples showed cytopathological changes in Vero cell lines. Further, indirect immunofluorescence antibody test and reverse transcriptase-polymerase chain reaction studies demonstrated the Chikungunya virus etiology during the episode. E1 gene sequence analysis has confirmed the involvement of the Central/East African genotype of the Chikungunya virus.

Host feeding pattern of Japanese encephalitis virus vector mosquitoes (Diptera: Culicidae) from Kuttanadu, Kerala, India

Identification of blood meals of vector mosquitoes is an important tool in the epidemiological investigations of vector-borne diseases. The blood meals of three mosquito species involved in the transmission of Japanese encephalitis virus (JEV) from the Kuttanadu area, Kerala, were determined using the agarose gel diffusion technique. A total of 4959 blood smears belonging to Culex (Culex) tritaeniorhynchus Giles (3273), Cx. (Culex) gelidus Theobald (64), Mansonia (Mnd.) indiana Edwards (735) ,and Ma. (Mnd.) uniformis (Theobald) (887) were tested. Cx. tritaeniorhynchus had predominantly fed on bovids (46.4%), and a good proportion (29%) had fed on more than one host. Cx. tritaeniorhynchus was highly zoophagic, and human feeding accounted for only 1.5% of those individuals successfully tested. Cx. gelidus showed bovid feeding at 36% and pig feeding at 12.5%. The test results showed 42.3% Ma. indiana and 12.2% Ma. uniformis had fed on humans. Multiple feeding was observed in Ma. indiana and Ma. uniformis, and most of the double feedings were from bovids and ovids (7.9 and 20.1%, respectively). Pig feeding accounted for 4.8% of the feedings by Cx. tritaeniorhynchus, 5.3% of Ma. indiana, and 6.4% of Ma. uniformis. This study is significant because of the role played by these mosquitoes in the transmission of JEV in the Kuttanadu area of Kerala, India.

Natural vertical transmission of dengue viruses by Aedes aegypti in Chennai, Tamil Nadu, India

BACKGROUND & OBJECTIVE

Dengue viruses are spread and maintained in an Aedes aegypti-human- Ae. aegypti cycle in urban areas of the tropics. Dengue viruses are also maintained in nature by vertical transmission by Ae. aegypti. A study was undertaken in Chennai, a known endemic city in south India, to comprehend the natural vertical transmission dynamics in Ae. aegypti and to assess its epidemiological importance.

METHODS

Ae. aegypti males collected in resting and landing collections were tested for dengue virus infection by antigen-capture enzyme-linked immunosorbent assay (ELISA) and further examined by insect bioassay, Toxorhynchites splendens inoculation-indirect immunofluorescence technique (Toxo-IFA) using serotype-specific monoclonal antibodies (Mabs), if found positive by ELISA.

RESULTS

Of the 509 pools of Ae. aegypti males (n=5408) screened, 15 pools, collected in April, June- July, November-December in 2003 and March, May in 2004, were found positive for dengue virus infection and the minimum infection rate (MIR) among adult males was high in June 2003 (28.0/ 1000). Three positive pools could be serotyped as dengue-2 (2 pools) and dengue-3 (1 pool).

INTERPRETATION & CONCLUSION

Dengue virus isolations from wild caught males of Ae. aegypti indicate the occurrence of transovarial transmission. Vertical transmission was mainly observed in summer months when dengue infections in humans were low suggesting that dengue viruses adopt a novel strategy of surviving adverse climatic conditions.

Desiccated vector mosquitoes used for the surveillance of Japanese encephalitis virus activity in endemic southern India

To monitor Japanese encephalitis virus (JEV) activity in endemic areas of Tamil Nadu, southern India, desiccated vector mosquitoes were screened for JEV antigen using ELISA, from 1996. A total of 133 233 specimens from eight index villages comprising 2816 pools (mainly Culex vishnui subgroup) were tested. Of these, 59 pools (2.1%) were positive for JEV antigen. Control measures were undertaken in positive villages accordingly. The average annual minimum infection rate was 0.8 at the beginning of the study and remained lower for nearly 8 years. A declining trend in JE cases was recorded.

Natural vertical transmission of dengue virus in Aedes albopictus (Diptera: Culicidae) in Kerala, a southern Indian state

The natural occurrence of vertical transmission of dengue viruses in Aedes albopictus (Skuse) mosquitoes was examined in the state of Kerala in southern India. Adults and larvae of Ae. albopictus collected from Kerala were screened for dengue viruses by using enzyme-linked immunosorbent assay with dengue-specific monoclonal antibodies. The possibility of the vertical transmission of dengue virus in Ae. albopictus was further evidenced by the detection of the virus in field-collected adult males as well as females emerged from field-collected larvae. Two pools, one pool from the adult males and one pool from the emerged females derived from field-collected larvae, were collected in the relatively hot months of June and March, respectively, and found to be positive for dengue virus antigen. Dengue serotype 2 virus was isolated from field-collected male adults in Kerala. These findings suggest that dengue virus is maintained in Ae. albopictus mosquitoes during the dry season by vertical transmission in nature.

Vector control complements mass drug administration against bancroftian filariasis in Tirukoilur, India

OBJECTIVE

To determine the role of vector control in further decreasing the transmission of bancroftian filariasis achieved by mass drug administration and the long-term impact on filariometric indices.

METHODS

Three rounds of annual mass drug administration, with diethylcarbamazine and ivermectin, were complemented by vector control (mainly using polystyrene beads) in villages of Tirukoilur, south India, during 1995-99. Subsequently, drug administration is being carried out with diethylcarbamazine and albendazole or diethylcarbamazine alone. We evaluated the impact of mass drug administration used alone or in conjunction with vector control (from 1995 to 2005) on vector transmission indices (such as transmission intensity index, monthly biting rate, monthly transmission potential and annual transmission potential). We analysed data on filarial infection in the community to estimate the prevalence of microfilaraemia and antigenaemia using chi2 analysis and Fisher's exact test.

FINDINGS

Vector density greatly decreased in villages where vector control was used as an adjunct to mass drug administration and almost no infective mosquitoes were found in the small numbers still remaining. Filarial antigenaemia was low and continued to decrease significantly in the age group 15-25 years in villages receiving mass drug administration with vector control in contrast to villages receiving only mass drug administration.

CONCLUSION

The gains of mass drug administration were sustained only with the integration of vector control measures. We advocate the incorporation of vector control in the Global Programme to Eliminate Lymphatic Filariasis as it can potentially decrease the time required for eliminating lymphatic filariasis.

Prediction of 3-dimensional structure of salivary odorant-binding protein-2 of the mosquito Culex quinquefasciatus, the vector of human lymphatic filariasis

Olfaction of insects is currently recognized as the major area of research for developing novel control strategies to prevent mosquito-borne infections. A 3-dimensional model (3D) was developed for the salivary gland odorant-binding protein-2 of the mosquito Culex quinquefasciatus, a major vector of human lymphatic filariasis. A homology modeling method was used for the prediction of the structure. For the modeling, two template proteins were obtained by mGenTHERADER, namely the high-resolution X-ray crystallography structure of a pheromone-binding protein (ASP1) of Apis mellifera L., [1R5R:A] and the aristolochene synthase from Penicillium roqueforti [1DI1:B]. By comparing the template protein a rough model was constructed for the target protein using MODELLER, a program for comparative modelling. The structure of OBP of the mosquito Culex quinquefasciatus resembles the structure of pheromone-binding protein ASP1 of Apis mellifera L., [1R5R:A]. From Ramachandran plot analysis it was found that the portion of residues falling into the most favoured regions was 86.0%. The predicted 3-D model may be further used in characterizing the protein in wet laboratory.