Reducing costs and operational constraints of dengue vector control by targeting productive breeding places: a multi-country non-inferiority cluster randomized trial.

OBJECTIVES: To test the non-inferiority hypothesis that a vector control approach targeting only the most productive water container types gives the same or greater reduction of the vector population as a non-targeted approach in different ecological settings and to analyse whether the targeted intervention is less costly. METHODS: Cluster randomized trial in eight study sites (Venezuela, Mexico, Peru, Kenya, Thailand, Myanmar, Vietnam, Philippines), with each study area divided into 18-20 clusters (sectors or neighbourhoods) of approximately 50-100 households each. Using a baseline pupal-demographic survey, the most productive container types were identified which produced >or=55% of all Ae. aegypti pupae. Clusters were then paired based on similar pupae per person indices. One cluster from each pair was randomly allocated to receive the targeted vector control intervention; the other received the 'blanket' (non-targeted) intervention attempting to reach all water holding containers. RESULTS: The pupal-demographic baseline survey showed a large variation of productive container types across all study sites. In four sites the vector control interventions in both study arms were insecticidal and in the other four sites, non-insecticidal (environmental management and/or biological control methods). Both approaches were associated with a reduction of outcome indicators in the targeted and non-targeted intervention arm of the six study sites where the follow up study was conducted (PPI, Pupae per Person Index and BI, Breteau Index). Targeted interventions were as effective as non-targeted ones in terms of PPI. The direct costs per house reached were lower in targeted intervention clusters than in non-targeted intervention clusters with only one exception, where the targeted intervention was delivered through staff-intensive social mobilization. CONCLUSIONS: Targeting only the most productive water container types (roughly half of all water holding container types) was as effective in lowering entomological indices as targeting all water holding containers at lower implementation costs. Further research is required to establish the most efficacious method or combination of methods for targeted dengue vector interventions.

Dengue research and training supported through the World Health Organization.

The rapidly increasing burden of dengue, the varied and often poorly understood factors contributing to its global spread, and the challenges of preventing and controlling it have led to a renewed call for more research and training on the disease. The main aims are to improve vector control, case management, and primary prevention through vaccine development. The World Health Organization (WHO), through its inter-departmental working group on dengue, is actively engaged in supporting and co-ordinating the major research activities. The dengue research initiatives of the Special Programme for Research and Training in Tropical Diseases (TDR), other departments at the WHO's Geneva headquarters, the WHO's regional and country offices, and the organization's dengue-affected member states are summarized in this article. This intensified effort, in close collaboration with other stakeholders, is contributing towards the goals of reversing the current epidemiological trends and of reducing the global burden posed by dengue in all of its forms.

Exploiting the potential of vector control for disease prevention.

Although vector control has proven highly effective in preventing disease transmission, it is not being used to its full potential, thereby depriving disadvantaged populations of the benefits of well tried and tested methods. Following the discovery of synthetic residual insecticides in the 1940s, large-scale programmes succeeded in bringing many of the important vector-borne diseases under control. By the late 1960s, most vector-borne diseases--with the exception of malaria in Africa--were no longer considered to be of primary public health importance. The result was that control programmes lapsed, resources dwindled, and specialists in vector control disappeared from public health units. Within two decades, many important vector-borne diseases had re-emerged or spread to new areas. The time has come to restore vector control to its key role in the prevention of disease transmission, albeit with an increased emphasis on multiple measures, whether pesticide-based or involving environmental modification, and with a strengthened managerial and operational capacity. Integrated vector management provides a sound conceptual framework for deployment of cost-effective and sustainable methods of vector control. This approach allows for full consideration of the complex determinants of disease transmission, including local disease ecology, the role of human activity in increasing risks of disease transmission, and the socioeconomic conditions of affected communities.

Control of Culex quinquefasciatus in pit latrines, using shredded, waste polystyrene.

As an alternative to the use of commercially available, expanded-polystyrene beads, a study was made of the effectiveness of shredded, waste polystyrene (SWAP) for the control of Culex quinquefasciatus. The relevant physical properties of the SWAP were first investigated in the laboratory. Then, under field conditions in wet pit latrines, mosquito emergence rates were measured before and after application of the material. In the laboratory, when compared with the commercial product, the irregular shape of the SWAP particles greatly reduced their capacity to spread over the water surface and the interstitial air spaces also permitted respiration and development of mosquito larvae. Nevertheless, under field conditions, with careful application of the SWAP over the water surfaces in wet pit latrines, almost complete control of mosquito breeding was observed within a few days. This was sustained for 60 days, at which time observations were discontinued. SWAP appears to offer an effective, cheap and readily available alternative to the commercial product for the control of C. quinquefasciatus. The practicality of using it in community-based, mosquito-control programmes warrants further study.

Community participation in dengue prevention and control: a survey of knowledge, attitudes, and practice in Trinidad and Tobago.

The priorities of public health planners are often at variance with the community's own environmental sanitation priorities and perspectives. Public opinion about individual, collective, and governmental responsibilities in addressing these issues and priorities is of particular importance when designing community-based programs. In a study conducted in Trinidad and Tobago on knowledge, attitudes, and practice regarding dengue, its prevention and control, a high level of awareness about dengue and its etiology was evident, but there was poor understanding of the symptoms and hence little concern about the health risks associated with it. The most important household pest problem identified by the respondents was related to mosquito nuisance, particularly from night-biting mosquitoes. Rodents were also a major concern perceived as being responsible for economic losses, ruined food, and a health hazard. Unreliable water supply, a factor associated with Aedes aegypti abundance, was an environmental sanitation issue of major importance to householders in rural areas. No correlation was found between knowledge of dengue and levels of Ae. aegypti abundance as measured by larval surveys of the respondents' premises. The study gave a clear indication of the need for broad-based environmental sanitation strategies when planning community-based vector control initiatives for the prevention and control of dengue in Trinidad and Tobago.

Mass chemotherapy with diethylcarbamazine for the control of Bancroftian filariasis: a twelve-year follow-up in northern Trinidad, including observations on Mansonella ozzardi.

A microfilaria survey was conducted in Trinidad in 1992, 12 years after mass treatment with spaced doses of diethylcarbamazine citrate (DEC-C) for the control of Bancroftian filariasis; 348 persons were examined using thick blood smears and a membrane filtration technique. They included 104 who had participated in the mass chemotherapy campaign in 1980. No Wuchereria bancrofti microfilariae were detected among 66% of the population examined. In 1980, 86 of 592 persons examined were found to be infected with W. bancrofti, 140 with Mansonella ozzardi and 44 with mixed infections, while in 1992, only M. ozzardi infections persisted despite treatment with DEC-C. Of the 104 persons reexamined 12 years later, 46 had M. ozzardi, of which five were new cases, but none had W. bancrofti. During both the 1980 and 1992 surveys, low microfilariae rates for M. ozzardi were observed among those 19 years of age or younger. Of the 302 persons newly examined in 1992, 29 were infected with significantly (P < 0.001) more males (79.3%) than females (20.9%) being microfilaremic. The combined results showed similar prevalence rates for M. ozzardi from 23.3% to 21.6% in 1980 and 1992. Nuclepore membrane filtration and thick blood films were very efficient in demonstrating the presence of microfilariae. The usefulness of these methods and spaced treatment using DEC-C are also discussed.

Mass chemotherapy with diethylcarbamazine for the control of Bancroftian Filariasis: a twelve-year follow-up in Northern Trinidad, including observations on Mansonella Ozzardi

A microfilaria survey was conducted in Trinidad in 1992, 12 years after mass treatment with spaced doses of diethylcarbamazine citrate (DEC-C) for the control of Bancroftian filariasis; 348 persons were examined using thick blood smears and a membrane filtration technique. They included 104 who had participated in the mass chemotherapy campaign in 1980. No Wuchereria bancrofti microfilariae were detected among 66 percent of the population examined. In 1980, 86 of 592 persons examined were found to be infected with W. bancrofti, 140 with Mansonella ozzardi and 44 with mixed infections, while in 1992, only M. ozzardi infections persisted despite treatment with DEC-C. Of the 104 persons re-examined 12 years later, 46 had M. ozzardi, of which five were new cases, but none had W. bancrofti. During both the 1980 and 1992 surveys, low microfilariae rates for M. ozzardi were observed among those 19 years of age or younger. Of the 302 persons newly examined in 1992, 29 were infected with significantly (P<0.001) more males (79.3 percent) than females (20.9 percent) being microfilaremic. The combined results showed similiar prevalence rates for M. ozzardi from 23.3 percent to 21.6 percent in 1980 and 1992. Nucleopore membrane filtration and thick blood films were very efficient in demonstrating the presence of microfilariae. The usefulness of these methods and spaced treatment using DEC-C are also discussed (AU)

Critical review of Aedes aegypti control programs in the Caribbean and selected neighboring countries.

In recent years the region of the Americas has experienced increasing dengue activity with circulation of multiple virus serotypes. Associated with this trend has been the occurrence of sporadic dengue hemorrhagic fever (DHF) cases and of DHF epidemics in both the Caribbean and Latin America. High vector infestation levels persist even though most countries in the Caribbean conduct national Aedes aegypti control programs and despite the fact that in some instances, expenditures exceed US$5 per capita per annum. This paper critically reviews the resources and vector control strategies employed in the region and in selected neighboring countries. Reasons for the lack of progress include continued overreliance on eradication-style larviciding routines and the passive role of communities in addressing the problem. A policy of health promotion aimed at improving environmental health practices at the household and community levels has been endorsed by the governments of the region but as yet has not been widely adopted.

Aedes aegypti infestation characteristics in several Caribbean countries and implications for integrated community-based control.

Periodic larval surveys for Aedes aegypti were conducted in 11 Caribbean countries between 1983 and 1989. On average, there were 24 potential larval habitats per house including 4.9 which held water at the time of examination. Breteau indices for the various islands ranged from 34.7 to 121.6. In descending order of importance, water storage drums, house plants, buckets, used tires and miscellaneous small discarded containers accounted for 84% of all foci. Highest rates of infestation were found in tires (38.4%) and drums (33.8%). For the development of integrated community-based vector control programs, not only should consideration be given to the larval ecology of Ae. aegypti, but also to the sociological significance of the various container habitats and the selection of control strategies most appropriate for their management.

Prevalence of Wuchereria bancrofti in Georgetown, Guyana.

A random sample bloodsmear survey was conducted during evening hours in Georgetown, Guyana, to determine the prevalence of Wuchereria bancrofti microfilariae. In all, 182 of 2,818 persons tested (6.5%) yielded positive results--indicating that the overall prevalence of Bancroftian filariasis has not diminished and may be on the rise. Relatively high prevalences found in children and adolescents point to active transmission. It appears likely that certain socioeconomic and environmental factors have been contributing to such transmission, and that similar factors could encourage increased transmission elsewhere in the Americas as well.

Bancroftian filariasis in coastal north Trinidad: the effects of mass chemotherapy using spaced doses of diethylcarbamazine citrate on human microfilaraemias and vector infection rates.

The effects of a mass chemotherapy programme using spaced doses of diethylcarbamazine citrate on Wuchereria bancrofti microfilaraemias and vector infection rates were studied in an isolated rural community of 650 people in north Trinidad where a microfilaria rate of 15% had previously been recorded. A single oral dose of 6 mg/kg body weight was given at monthly intervals for one year. After 6 months, 79% (52/66) of persons previously microfilaraemic had become negative. After 12 months the negative proportion had increased to 90% (63/70). The geometric mean microfilaria density of those still microfilaraemic was reduced from 19.7 to 4.6 per 100 mm3 of blood. Of 147 initially negative persons, none had become positive following treatment. Filarial infection rates in Culex quinquefasciatus from randomly sampled houses fell from 6.4% to zero; in houses where occupants with microfilaraemia had been identified before treatment, the rate was reduced from 15.8% to zero. In a supplementary study, however, weekly collections from one initially positive house showed a rapid decline in the vector infection rate from 43% to 2% after three months but an additional 3 months elapsed before the index reached zero. There was negligible microfilarial uptake by the vectors from residual low-density microfilaraemias (less than 10 microfilariae per 100 mm3 of blood) after chemotherapy.

Filariasis in Amerindians of western Guyana with observations on transmission of Mansonella ozzardi by a Simulium species of the amazonicum group.

In order to conduct experimental infection studies of Mansonella ozzardi in local haematophagous Diptera, volunteers infected with this parasite were identified during a microfilaria survey in four Amerindian villages in the Pakaraima Mountains of western Guyana, near the Brazilian border. M. ozzardi microfilariae were detected in thick blood smears from 8-21% of persons examined. They were also found in skin snips from 8/73 persons all of whom were positive by blood smear examination. No Onchocerca volvulus microfilariae were detected. Dipetalonema perstans infections were found in three of the four villages but prevalence rates were only 1-8%. Manbaited catches of haematophagous Diptera made at the onset of the dry season in one of the villages yielded only three Simulium species. After flies were engorged on infected volunteers, M. ozzardi larvae developed to the infective stage in 6-7 days in the most abundant species, a member of the Simulium amazonicum group. Man-biting rates of up to 156 per 15-minute period were recorded for this species in midday collections along river banks near one of the villages. Developing filariae, including infective larvae of M. ozzardi, were also found in wild-caught flies. It was concluded that this Simulium species is a vector of M. ozzardi in the study area.

Parasitological and clinical studies of Wuchereria bancrofti and Mansonella ozzardi in coastal north Trinidad, West Indies.

PIP: A parasitological and clinical survey of Wuchereria bancrofti and Mansonella ozzardi was conducted in Blanchisseuse, an isolated rural community of 650 people in coastal north Trinidad. W. bancrofti microfilariae were found in 15% of the resident population and the prevalence was higher in males (19%) than in females (12%). Microfilaraemias were undetected in children under 5 years of age but 12% of children and adolescents between 5 and 19 years of age were positive. Microfilaraemias were most common in males aged 40-59 years (34%) and in females in the same age group (21%). Whereas geometric mean microfilaria densities were generally higher in females than in males under 40 years old, in the older age groups the pattern was reversed, the difference being especially pronounced in the over 60s. There were more than 2 times as many males with M. ozzardi microfilariae (35%) than there were females (15%). The prevalence was low in children and young adults but increased with age thereafter. In the older age groups microfilaria densities followed a similar trend. Genital signs compatible with lymphatic filarial disease were seen in 29% of males; these included hydrocoele (15%) and elephantiasis of the scrotum (1%). Most signs were seen in persons over 50 years of age. 6% of females had lymphoedema of the leg(s), and in 4 cases (2.3%) this had progressed to elephantiasis. A positive association was found between M. ozzardi microfilaraemia and clinical history of articular pain. The findings suggest that both filarial species are of some public health significance in at least 1 rural area of Trinidad, and they provide a basis for the development of a lymphatic filariasis control strategy in the community.^ieng