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.

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

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.

Erradicacion de Aedes aegypti en Caiman Brac y Pequeno Caiman, Antillas Britanicas, con Abate (Temephos) en 1970-1972. / Erradication of Aedes aegypti in Cayman Brac and Little Cayman, West Indies, with Abate (Temephos) in 1970-1972

En 1970-1972, una campana intensiva contra ejemplares de adultos y larvas de Aedes aegypti logro erradicar el mosquito de las Islas Caimanes Menores. Esta descripcion de los problemas encontrados y las medidas tomadas, suministra informacion util para quienes se ocupan de la erradicacion del A. aegypti.

Bancroftian filariasis in coastal North Trinidad, West Indies: intensity of transmission by Culex quinquefasciatus.

The intensity of transmission of Wuchereria bancrofti was measured in a coastal community in north Trinidad where 15% of the residents were microfilaraemic. The only significant vector, Culex quinquefasciatus, was studied in detail to determine seasonal abundance, longevity, infection and infectivity rates. Only 2.1% of the indoor biting population and 7.0% of the indoor resting population were infected. The daily mortality rate of the vector increased with age from 27% at four days to 44 to 47% at 12 days and is considered to be an important factor contributing to the low infectivity rate (0.1%). The mean number of C. quinquefasciatus bites received by a resident of the village during the year of observation was estimated to be 17,948 of which 14 were from mosquitoes harbouring infective larvae of W. bancrofti. The results from similar studies elsewhere are outlined, but the need for standardization of procedure is emphasized before more reliable comparisons can be made.

The prevalence and distribution of Mansonella ozzardi in coastal north Trinidad, W.I.

A day blood smear survey for Mansonella ozzardi in the north coast communities of Trinidad recorded a prevalence of 4.8% in 4,488 persons examined. Prevalence rates were highest in the four western-most communities, where the vector, Culicoides phlebotomus, is a severe nuisance problem. Prevalence rates increased with age and were higher in males than in females. Mean microfilaria densities were low in both sexes up to 50 years of age but in older males the density increased with age. Wuchereria bancrofti infections were detected in five of the ten communities surveyed.

Erradicación de Aedes aegypty en Caimán Brac y Pequeño Caimán, Antillas Británicas, con Abate (Temephos) en 1970-1972 / Eradication of Aedes aegypty on Cayman Brac and Little Caima, West Indies, con Abate (Temephos) in 1970-1972

En 1970-1972, una campaña intensiva contra ejemplares de adultos y larvas de Aedes aegypty logró erradicar el mosquito de las Islas Caimanes Menores. Esta descripción de los problemas encontrados y las medidas tomadas, suministra información útil para quienes se ocupan de la erradicación del A. aegypti (AU)