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.

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.

The treatment of visceral leishmaniasis (kala-azar) in India: no obvious signs of long-term success.

In India, the eastern state of Bihar is particularly badly affected by visceral leishmaniasis (VL). It was in Bihar in the 1980s that the first clear signs of resistance to pentavalent antimonials, which had then been the standard antileishmanial treatment for several decades, were observed. New drugs and new formulations of old drugs have since been developed for the treatment of VL. However, despite some initial signs of benefit after each major revision in the method of treatment of VL in India, the VL-related case fatality rates recorded in India since the 1970s show no clear evidence of long-term success. In fact, the most recent data indicate that such rates have stabilised or even increased, probably because of the continued usage of sodium stibogluconate in northern Bihar.

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.

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.