Evaluation of insecticide treated window curtains and water container covers for dengue vector control in a large-scale cluster-randomized trial in Venezuela.

BACKGROUND: Following earlier trials indicating that their potential in dengue vector control was constrained by housing structure, a large-scale cluster-randomized trial of insecticide treated curtains (ITCs) and water jar covers (ITJCs) was undertaken in Venezuela. METHODS: In Trujillo, Venezuela, 60 clusters (6223 houses total) were randomized so that 15 clusters each received either PermaNet insecticide-treated window curtains (ITCs), permanent insecticide-treated water storage jar covers (ITJCs), a combination of both ITCs and ITJCs, or no insecticide treated materials (ITMs). A further 15 clusters located at least 5km from the edge of the study site were selected to act as an external control. Entomological surveys were carried out immediately before and after intervention, and then at 6-month intervals over the following 27 months. The Breteau and House indices were used as primary outcome measures and ovitrap indices as secondary. Negative binomial regression models were used to compare cluster-level values of these indices between the trial arms. RESULTS: Reductions in entomological indices followed deployment of all ITMs and throughout the trial, indices in the external control arm remained substantially higher than in the ITM study arms including the internal control. Comparing the ratios of between-arm means to summarise the entomological indices throughout the study, the combined ITC+ITJC intervention had the greatest impact on the indices, with a 63% difference in the pupae per person indices between the ITC+ITJC arm and the internal control. However, coverage had fallen below 60% by 14-months post-intervention and remained below 40% for most of the remaining study period. CONCLUSIONS: ITMs can impact dengue vector populations in the long term, particularly when ITCs and ITJCs are deployed in combination. TRIAL REGISTRATION: ClinicalTrials.gov ISRCTN08474420; www.isrctn.com.

Population structure of the dengue viruses, Aragua, Venezuela, 2006-2007. Insights into dengue evolution under hyperendemic transmission.

During the past three decades there has been a notable increase in dengue disease severity in Venezuela. Nevertheless, the population structure of the viruses being transmitted in this country is not well understood. Here, we present a molecular epidemiological study on dengue viruses (DENV) circulating in Aragua State, Venezuela during 2006-2007. Twenty-one DENV full-length genomes representing all of the four serotypes were amplified and sequenced directly from the serum samples. Notably, only DENV-2 was associated with severe disease. Phylogenetic trees constructed using Bayesian methods indicated that only one genotype was circulating for each serotype. However, extensive viral genetic diversity was found in DENV isolated from the same area during the same period, indicating significant in situ evolution since the introduction of these genotypes. Collectively, the results suggest that the non-structural (NS) proteins may play an important role in DENV evolution, particularly NS1, NS2A and NS4B proteins. The phylogenetic data provide evidence to suggest that multiple introductions of DENV have occurred from the Latin American region into Venezuela and vice versa. The implications of the significant viral genetic diversity generated during hyperendemic transmission, particularly in NS protein are discussed and considered in the context of future development and use of human monoclonal antibodies as antivirals and tetravalent vaccines.

Multicentre prospective study on dengue classification in four South-east Asian and three Latin American countries.

OBJECTIVE: To evaluate the existing WHO dengue classification across all age groups and a wide geographical range and to develop a revised evidence-based classification that would better reflect clinical severity. METHODS: We followed suspected dengue cases daily in seven countries across South-east Asia and Latin America and then categorised them into one of three intervention groups describing disease severity according to the overall level of medical and nursing support required. Using a pre-defined analysis plan, we explored the clinical and laboratory profiles characteristic of these intervention categories and presented the most promising options for a revised classification scheme to an independent group of WHO dengue experts for consideration. Potential warning signs were also evaluated by comparing contemporaneous data of patients who progressed to severe disease with the data of those who did not. RESULTS: A total of 2259 patients were recruited during 2006-2007 and 230 (13%) of the 1734 laboratory-confirmed patients required major intervention. Applying the existing WHO system, 47/210 (22%) of patients with shock did not fulfil all the criteria for dengue haemorrhagic fever. However, no three-tier revision adequately described the different severity groups either. Inclusion of readily discernible complications (shock/severe vascular leakage and/or severe bleeding and/or severe organ dysfunction) was necessary to devise a system that identified patients requiring major intervention with sufficient sensitivity and specificity to be practically useful. Only a small number of subjects (5%) progressed to severe disease while under observation; several warning signs were identified, but much larger studies are necessary to fully characterize features associated with disease progression. CONCLUSIONS: Based on these results, a revised classification system comprised of two entities, 'Dengue' and 'Severe Dengue', was proposed and has now been incorporated into the new WHO guidelines.

The cost of routine Aedes aegypti control and of insecticide-treated curtain implementation.

Insecticide-treated curtains (ITCs) are promoted for controlling the Dengue vector Aedes aegypti. We assessed the cost of the routine Aedes control program (RACP) and the cost of ITC implementation through the RACP and health committees in Venezuela and through health volunteers in Thailand. The yearly cost of the RACP per household amounted to US$2.14 and $1.89, respectively. The ITC implementation cost over three times more, depending on the channel used. In Venezuela the RACP was the most efficient implementation-channel. It spent US$1.90 (95% confidence interval [CI]: 1.83; 1.97) per curtain distributed, of which 76.9% for the curtain itself. Implementation by health committees cost significantly (P = 0.02) more: US$2.32 (95% CI: 1.93; 2.61) of which 63% for the curtain. For ITC implementation to be at least as cost-effective as the RACP, at equal effectiveness and actual ITC prices, the attained curtain coverage and the adulticiding effect should last for 3 years.

Evaluation of the effectiveness of insecticide treated materials for household level dengue vector control.

OBJECTIVE: To assess the operational effectiveness of long-lasting insecticide treated materials (ITMs), when used at household level, for the control of Aedes aegypti in moderately infested urban and suburban areas. METHODS: In an intervention study, ITMs consisting of curtains and water jar-covers (made from PermaNet) were distributed under routine field conditions in 10 clusters (5 urban and 5 suburban), with over 4000 houses, in Trujillo, Venezuela. Impact of the interventions were determined by comparing pre-and post-intervention measures of the Breteau index (BI, number of positive containers/100 houses) and pupae per person index (PPI), and by comparison with indices from untreated areas of the same municipalities. The effect of ITM coverage was modeled. RESULTS: At distribution, the proportion of households with ≥1 ITM curtain was 79.7% in urban and 75.2% in suburban clusters, but decreased to 32.3% and 39.0%, respectively, after 18 months. The corresponding figures for the proportion of jars using ITM covers were 34.0% and 50.8% at distribution and 17.0% and 21.0% after 18 months, respectively. Prior to intervention, the BI was 8.5 in urban clusters and 42.4 in suburban clusters, and the PPI was 0.2 and 0.9, respectively. In both urban and suburban clusters, the BI showed a sustained 55% decrease, while no discernable pattern was observed at the municipal level. After controlling for confounding factors, the percentage ITM curtain coverage, but not ITM jar-cover coverage, was significantly associated with both entomological indices (Incidence Rate Ratio = 0.98; 95%CI 0.97-0.99). The IRR implied that ITM curtain coverage of at least 50% was necessary to reduce A. aegypti infestation levels by 50%. CONCLUSION: Deployment of insecticide treated window curtains in households can result in significant reductions in A. aegypti levels when dengue vector infestations are moderate, but the magnitude of the effect depends on the coverage attained, which itself can decline rapidly over time.

Usefulness and applicability of the revised dengue case classification by disease: multi-centre study in 18 countries.

BACKGROUND: In view of the long term discussion on the appropriateness of the dengue classification into dengue fever (DF), dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS), the World Health Organization (WHO) has outlined in its new global dengue guidelines a revised classification into levels of severity: dengue fever with an intermediary group of "dengue fever with warning sings", and severe dengue. The objective of this paper was to compare the two classification systems regarding applicability in clinical practice and surveillance, as well as user-friendliness and acceptance by health staff. METHODS: A mix of quantitative (prospective and retrospective review of medical charts by expert reviewers, formal staff interviews), semi-quantitative (open questions in staff interviews) and qualitative methods (focus group discussions) were used in 18 countries. Quality control of data collected was undertaken by external monitors. RESULTS: The applicability of the DF/DHF/DSS classification was limited, even when strict DHF criteria were not applied (13.7% of dengue cases could not be classified using the DF/DHF/DSS classification by experienced reviewers, compared to only 1.6% with the revised classification). The fact that some severe dengue cases could not be classified in the DF/DHF/DSS system was of particular concern. Both acceptance and perceived user-friendliness of the revised system were high, particularly in relation to triage and case management. The applicability of the revised classification to retrospective data sets (of importance for dengue surveillance) was also favourable. However, the need for training, dissemination and further research on the warning signs was highlighted. CONCLUSIONS: The revised dengue classification has a high potential for facilitating dengue case management and surveillance.

Multi-country evaluation of the sensitivity and specificity of two commercially-available NS1 ELISA assays for dengue diagnosis.

BACKGROUND: Early diagnosis of dengue can assist patient triage and management and prevent unnecessary treatments and interventions. Commercially available assays that detect the dengue virus protein NS1 in the plasma/serum of patients offers the possibility of early and rapid diagnosis. METHODOLOGY/PRINCIPAL FINDINGS: The sensitivity and specificity of the Pan-E Dengue Early ELISA and the Platelia Dengue NS1 Ag assays were compared against a reference diagnosis in 1385 patients in 6 countries in Asia and the Americas. Platelia was more sensitive (66%) than Pan-E (52%) in confirmed dengue cases. Sensitivity varied by geographic region, with both assays generally being more sensitive in patients from SE Asia than the Americas. Both kits were more sensitive for specimens collected within the first few days of illness onset relative to later time points. Pan-E and Platelia were both 100% specific in febrile patients without evidence of acute dengue. In patients with other confirmed diagnoses and healthy blood donors, Platelia was more specific (100%) than Pan-E (90%). For Platelia, when either the NS1 test or the IgM test on the acute sample was positive, the sensitivity versus the reference result was 82% in samples collected in the first four days of fever. NS1 sensitivity was not associated to disease severity (DF or DHF) in the Platelia test, whereas a trend for higher sensitivity in DHF cases was seen in the Pan-E test (however combined with lower overall sensitivity). CONCLUSIONS/SIGNIFICANCE: Collectively, this multi-country study suggests that the best performing NS1 assay (Platelia) had moderate sensitivity (median 64%, range 34-76%) and high specificity (100%) for the diagnosis of dengue. The poor sensitivity of the evaluated assays in some geographical regions suggests further assessments are needed. The combination of NS1 and IgM detection in samples collected in the first few days of fever increased the overall dengue diagnostic sensitivity.

Effective control of dengue vectors with curtains and water container covers treated with insecticide in Mexico and Venezuela: cluster randomised trials.

OBJECTIVES: To measure the impact on the dengue vector population (Aedes aegypti) and disease transmission of window curtains and water container covers treated with insecticide. DESIGN: Cluster randomised controlled trial based on entomological surveys and, for Trujillo only, serological survey. In addition, each site had a non-randomised external control. SETTING: 18 urban sectors in Veracruz (Mexico) and 18 in Trujillo (Venezuela). PARTICIPANTS: 4743 inhabitants (1095 houses) in Veracruz and 5306 inhabitants (1122 houses) in Trujillo. INTERVENTION: Sectors were paired according to entomological indices, and one sector in each pair was randomly allocated to receive treatment. In Veracruz, the intervention comprised curtains treated with lambdacyhalothrin and water treatment with pyriproxyfen chips (an insect growth regulator). In Trujillo, the intervention comprised curtains treated with longlasting deltamethrin (PermaNet) plus water jar covers of the same material. Follow-up surveys were conducted at intervals, with the final survey after 12 months in Veracruz and nine months in Trujillo. MAIN OUTCOME MEASURES: Reduction in entomological indices, specifically the Breteau and house indices. RESULTS: In both study sites, indices at the end of the trial were significantly lower than those at baseline, though with no significant differences between control and intervention arms. The mean Breteau index dropped from 60% (intervention clusters) and 113% (control) to 7% (intervention) and 12% (control) in Veracruz and from 38% to 11% (intervention) and from 34% to 17% (control) in Trujillo. The pupae per person and container indices showed similar patterns. In contrast, in nearby communities not in the trial the entomological indices followed the rainfall pattern. The intervention reduced mosquito populations in neighbouring control clusters (spill-over effect); and houses closer to treated houses were less likely to have infestations than those further away. This created a community effect whereby mosquito numbers were reduced throughout the study site. The observed effects were probably associated with the use of materials treated with insecticide at both sites because in Veracruz, people did not accept and use the pyriproxyfen chips. CONCLUSION: Window curtains and domestic water container covers treated with insecticide can reduce densities of dengue vectors to low levels and potentially affect dengue transmission.

The Buen Pastor cemetery in Trujillo, Venezuela: measuring dengue vector output from a public area.

As vector control of dengue typically targets individual households to eliminate breeding sites or control adult mosquitoes during epidemics, public spaces are frequently neglected. To investigate the importance of such places as sources of dengue vectors, a study of Aedes aegypti productivity in a cemetery in northern Venezuela, using standard entomological indices for assessing dengue vector infestations, was carried out in the wet season in May 2003. Containers were found on 72.8% of graves; 44% of the containers held water and in 46.9% of these we found A. aegypti larvae and/or pupae. The average density of Aedes-infested containers was 39 per hectare. There were no significant differences in infestation rates between container types (vases, planters or others) or materials (cement, plastic, glass, etc.). Containers with 1-5 l of water held the greatest proportion of the pupae found in the cemetery (46.7%); containers with <100 ml of water contained no pupae. The mean number of pupae produced in the cemetery was estimated at 4185 pupae/ha per 48 h and the daily output of potential vector mosquitoes from the entire cemetery was calculated at approximately 3000 females per day. These mosquitoes presumably left the cemetery to feed in the nearby communities, thus thwarting the environmental management and health education programmes that had reduced household dengue vector infestations. The study shows the importance of public places as sources of dengue vectors in urban areas, and the need to include such areas in vector control programmes.

Prevention of the transmission of Chagas' disease with pyrethroid-impregnated materials.

Interrupting the transmission of Chagas' disease using insecticide-treated materials could be a cost-effective option, particularly for sylvatic vectors, which enter houses at night. A randomized trial was undertaken that included all houses in two communities in regions endemic for this disease, one in Venezuela (50 houses) and one in Colombia (47 houses). After a baseline study (including a short questionnaire survey, entomologic assessment, and Chagas' disease serology), each household was randomly allocated to either the intervention group, which used pyrethroid-impregnated bed nets, or the control group, which used unimpregnated bed nets. Serologic analysis of children in the baseline study showed active transmission of Chagas' disease in the Venezuelan community (10.7% of 103 children were positive), but none in the Colombian community (0% of 100 children were positive). Vectors were sylvatic and bugs entered the houses at night in both communities. The efficacy of pyrethroids against triatomine vectors was tested in Venezuela by exposing Rhodnius prolixus to lambdacyhalothrin-impregnated fabrics and in Colombia by residual house spraying with deltamethrin. This randomized trial showed that in both countries users of impregnated bed nets were well protected from vector bites (immediate benefit). The long-term effect on the community was high vector mortality. In Venezuela, all 62 vectors detected (mainly R. robustus) died within 72 hours of contact with impregnated bed nets. In houses that used unimpregnated nets, only 24.5% (13 of 53) of the vectors died (P < 0.001). The vectors most likely came from infested palm trees and they maintained transmission of the disease in this community (28.1% of 629 R. robustus were positive for Trypanosoma cruzi). Bioassays showed that the mortality rate of R. prolixus was 100% on lambda-cyhalothrin-impregnated materials. In addition, in Colombia (the main vector was R. prolixus), the effect of repellent on vectors (driving them away from impregnated nets) was significant. Thus, users of impregnated bed nets are well protected from transmission of Chagas' disease, and vector reduction or elimination can potentially be achieved in areas infested with R. prolixus and R. robustus.

Mesofauna de criaderos naturales de anopheles spp. y las poblaciones depredadoras de sus larvas / Mesofauna of naturals breeding of anopheles spp. and the predator of larval population

Se estudia la flora, mesofauna y depredadores de larvas de 22 humedales criaderos de Anopheles albimanus ubicados en una transecta desde el estado Trujillo (9º34'N y 70º37'0) entre altitudes comprendidas desde los 547 hasta los 19 msnm. Se observó una relación inversa entre el número de larvas de An.albimanus y An.triannulatus en criaderos permanentes soleados, así como una relación directa entre hidrofilas y la presencia de an.albimanus. Se evidenció depredación natural de larvas Anopheles sp por larvas de Odonata mediante la técnica de Elisa. No se observó ninguna relación importante entre las características fisicoquímicas del agua y del suelo de los humedales, con la fauna culicida