Enhancing the evidence base for health impact assessment.

Health impact assessment differs from other purposes for which evidence is collated in a number of ways, including:the focus on complex interventions or policy and their diverse effects on determinants of health;the need for evidence on the reversibility of adverse factors damaging to health;the diversity of the evidence in terms of relevant disciplines, study designs, quality criteria and sources of information;the broad range of stakeholders involved;the short timescale and limited resources generally available;the pragmatic need to inform decision makers regardless of the quality of the evidence. These have implications for commissioning and conducting reviews. Methods must be developed to: facilitate comprehensive searching across a broad range of disciplines and information sources; collate appropriate quality criteria to assess a range of study designs; synthesise different kinds of evidence; and facilitate timely stakeholder involvement. Good practice standards for reviews are needed to reduce the risk of poor quality recommendations. Advice to decision makers must make explicit limitations resulting from absent, conflicting, or poor quality evidence.

Climate change and malaria transmission.

There is a consensus among climatologists that our planet is experiencing a progressive rise in surface temperature due to the increased production of "greenhouse" gases. Some of the possible consequences of elevated temperature on malaria transmission are examined in the present review. A simple mathematical model is first used to examine the effect of temperature on the ability of Anopheles maculipennis to transmit vivax malaria. This indicates that small increases in temperature at low temperatures may increase the risk of transmission substantially. This is important, since vulnerable communities, poorly protected by health services, in areas of unstable or no malaria are likely to be at increased risk of future outbreaks. In contrast, areas of stable transmission may be little affected by rising temperature. It is thought that global warming will lead to coastal flooding, changes in precipitation and, indirectly, changes in land use. Just how these changes will effect transmission at a regional level requires an understanding of the ecology of local vectors, since environmental changes which favour malaria transmission in one vector species may reduce it in another. Methods for predicting future changes in malaria in different regions are discussed, highlighting the need for further research in this area. Most importantly, there is a need for researchers to validate the accuracy of the models used for predicting malaria and to confirm the assumptions on which the models are based.

A survey of larval and adult mosquitoes on the flood plains of Bangladesh, in relation to flood-control activities.

A mosquito survey was carried out between October 1991 and November 1992 on the flood plains of Bangladesh, as part of a baseline study designed to help predict the effects on vector-borne diseases of embanking rivers under the Bangladesh Government's Flood Action Plan. Overall, 15 species of larval and 15 species of adult anophelines were collected, along with 13 larval and 21 adult culicines. Anophelines made up only 6% of the mosquitoes caught at human bait. The most abundant anopheline biting man was Anopheles vagus, the dominant species in all nine sampling villages. The other recognized malaria vectors in the flood plains of Bangladesh, namely An. philippinensis, An. aconitus and An. annularis, were collected but in relatively low numbers. Culex vishnui was the most abundant biting culicine in all villages. Biting mosquitoes showed a bimodal seasonality of biting, with peaks between February and April and September and October. All biting mosquitoes showed a significant preference for outdoor biting. The densities of the mosquito populations are more likely to be affected by the large-scale environmental changes which have occurred in Bangladesh, as well as the dramatic increase in the density of the human population, than by the river embankments per se.

Comparative effects of permethrin-impregnated bednets and DDT house spraying on survival rates and oviposition interval of Anopheles farauti No. 1 (Diptera:Culicidae) in Solomon Islands.

Human-biting, CDC light trap and pig-baited collections were used to monitor changes in the abundance and parity rate of Anopheles farauti No. 1 mosquitoes in three Solomon Islands villages for 30 consecutive nights. Houses in one of the villages were sprayed with DDT, another village was unsprayed but its inhabitants used permethrin-treated bednets and the third village was left completely untreated. Mosquitoes collected each day were dissected to determine follicular maturation and parity. In the second year of vector control, survival rates (determined by time-series analysis of the landing catches and biting parous population) were significantly lower in the village using permethrin-treated bednets than in the other two villages. There was no difference in the estimated survival rates between the untreated and DDT-sprayed villages. The oviposition cycle was extended to 4 days in the permethrin-treated village compared with 3 days in the other villages. The expected infective life was 1.75-fold longer in the untreated village than in the permethrin-treated village. The epidemiological implications of replacing DDT spraying with permethrin for malaria control are discussed.

Assessing health opportunities: a course on multisectoral planning.

Multisectoral planning can yield major benefits for health, especially in the case of water resource development projects. A two-week course, designed to involve mid-level officers from at least six government ministries in the planning and implementation of such projects, has been tested in Ghana, the United Republic of Tanzania, and Zimbabwe.

Size variation and reproductive success in the mosquito Aedes cantans.

A link between density-dependent larval competition and adult size of the mosquito Aedes cantans was demonstrated in northern England. Ponds containing high larval densities produced smaller larvae which, in turn, resulted in smaller adults at emergence. In both 1989 and 1990, parous mosquitoes caught at human bait were larger than nulliparous ones, suggesting that larger mosquitoes are more successful at host location and egg-laying and also that they may be longer lived. Larger mosquitoes produced larger egg clutches than smaller females: however, there was no difference in the size of eggs laid by large and small females.

Host finding, feeding patterns and evidence for a memorized home range of the mosquito Aedes cantans.

ELISA tests of Aedes cantans bloodmeals in woodland near Liverpool during 1989 and 1990, revealed preferences for sheep and cows, these hosts representing more than 60% of the total. Dispersal studies carried out on newly-emerged adults and those caught at human bait, indicated that individuals move freely between the two woods studied, mixing as a single population. Mean recapture rates for mosquitoes marked with paint were 2.28% in 1989 and 6.3% in 1990. Recapture rates for mosquitoes marked with powder were 3.66% in 1989 and 6.25% in 1990. The patterns of dispersal of adult females suggest that Aedes cantans has a learned and memorized familiar area map and possesses a sense of location.

An historical review of malaria, kala-azar and filariasis in Bangladesh in relation to the Flood Action Plan.

This paper reviews the evidence of a link between flood control and vector-borne disease in Bengal/Bangladesh. Malaria is historically associated with reduced flooding and embankment construction in the flood plains of Bengal. The land west and south of the Jamuna river was highly malarious in 1916 but is not so today. The lands east of the Jamuna now have a higher, though still small, risk. The reduction in health risk can be attributed to the intensification of land use and human population density. Although there are many mosquito species, the abundance of the former malaria vector appears to have declined as environmental change removed its breeding sites. Visceral leishmaniasis (kala-azar) is a serious disease which is fatal if left untreated. It occurs in irregular, periodic epidemics and is currently increasing in Bangladesh. In the past, malaria and kala-azar were confused and the prevalence of both may have been increased by embankment programmes. Both diseases are unstable and there is insufficient historical information to predict, with certainty, the consequences of environmental change. Reduced flooding accompanied by increased pollution will probably control the malaria vector. More information is needed about the response of the kala-azar vector to flooding. Bancroftian filariasis is non-fatal but causes chronic morbidity. It has had a widespread but usually low prevalence in Bangladesh, with both rural and urban foci. There are few recent data. Increasing organic pollution and drainage obstruction are expected to favour the vector and increase transmission.

Deforestation: effects on vector-borne disease.

This review addresses changes in the ecology of vectors and epidemiology of vector-borne diseases which result from deforestation. Selected examples are considered from viral and parasitic infections (arboviruses, malaria, the leishmaniases, filariases, Chagas Disease and schistosomiasis) where disease patterns have been directly or indirectly influenced by loss of natural tropical forests. A wide range of activities have resulted in deforestation. These include colonisation and settlement, transmigrant programmes, logging, agricultural activities to provide for cash crops, mining, hydropower development and fuelwood collection. Each activity influences the prevalence, incidence and distribution of vector-borne disease. Three main regions are considered--South America, West & Central Africa and South-East Asia. In each, documented changes in vector ecology and behaviour and disease pattern have occurred. Such changes result from human activity at the forest interface and within the forest. They include both deforestation and reafforestation programmes. Deforestation, or activities associated with it, have produced new habitats for Anopheles darlingi mosquitoes and have caused malaria epidemics in South America. The different species complexes in South-East Asia (A. dirus, A. minimus, A. balabacensis) have been affected in different ways by forest clearance with different impacts on malaria incidence. The ability of zoophilic vectors to adapt to human blood as an alternative source of food and to become associated with human dwellings (peridomestic behaviour) have influenced the distribution of the leishmaniases in South America. Certain species of sandflies (Lutzomyia intermedia, Lu. longipalpis, Lu. whitmani), which were originally zoophilic and sylvatic, have adapted to feeding on humans in peridomestic and even periurban situations. The changes in behaviour of reservoir hosts and the ability of pathogens to adapt to new reservoir hosts in the newly-created habitats also influence the patterns of disease. In anthroponotic infections, such as Plasmodium, Onchocerca and Wuchereria, changes in disease patterns and vector ecology may be more difficult to detect. Detailed knowledge of vector species and species complexes is needed in relation to changing climate associated with deforestation. The distributions of the Anopheles gambiae and Simulium damnosum species complexes in West Africa are examples. There have been detailed longitudinal studies of Anopheles gambiae populations in different ecological zones of West Africa. Studies on Simulium damnosum cytoforms (using chromosome identification methods) in the Onchocerciasis Control Programme were necessary to detect changes in distribution of species in relation to changed habitats. These examples underline the need for studies on the taxonomy of medically-important insects in parallel with long-term observations on changing habitats.(ABSTRACT TRUNCATED AT 400 WORDS)

Description and performance of an updraft trap for sandflies.

An updraft trap for sampling sandflies in the field was developed and tested in the Marigat area of Baringo District, Kenya. The main components of the trap were a 12 cm long plastic drain pipe, 9 V d.c. electric motor, aluminium fan and a perspex sandfly collection cage. Comparisons of the updraft trap with a CDC and a 1 x 1 m polythene sheet coated with castor oil (sticky trap) showed the former was more consistent than the other traps in sampling sandflies from animal burrows. A total of 1241 sandflies belonging to eleven species were collected. Sergentomyia bedfordi, Phlebotomus martini, S. antennatus and P. duboscqi were the commonest species comprising 32.5%, 27.0%, 21.1% and 11.3% of the total catch respectively. However, the relative proportion of the different species varied according to the type of trap used. The CDC trap apparently attracted the known vectors of leishmaniases in the area, P. martini and P. duboscqi. Significantly more male than female P. martini and S. antennatus were collected by the various traps. A significantly higher proportion of female S. bedfordi was captured by the updraft and sticky traps while equal numbers of male and female P. duboscqi were collected in all traps.

Estimation of survival rate and oviposition interval of Anopheles balabacensis mosquitoes from mark-recapture experiments in Sabah, Malaysia.

An exophilic population of the vector mosquito Anopheles balabacensis Baisas was investigated in two mark-recapture studies (16.ix-13.x.1986 and 6-26.i.1987) at an inland, foothill village in Sabah, Malaysia. Wild female mosquitoes were intercepted as they came to feed on man or buffalo, given a bloodmeal, marked with fluorescent dust and released. The recapture rate was about 12%. A new method of analysis is proposed which uses cross-correlation and a time series model. The estimated survival per oviposition cycle was 0.48-0.54 and the oviposition cycle interval 2-3 days.

The effect of moonlight and other factors on the oviposition cycle of malaria vectors in Madang, Papua New Guinea.

A series of capture-recapture experiments were undertaken in a coastal village of Papua New Guinea throughout a complete lunar cycle at the end of the dry season in 1987. The duration of the oviposition cycle of mosquitoes released blood-fed in their village of capture was 2.04 days at the full moon and increased to 2.4 days during moonless periods. Mosquitoes displaced 4 km from their village of origin demonstrated an oviposition cycle of longer duration than that of mosquitoes displaced 0-1.5 km. Approximately 25% of Anopheles farauti dispersed between adjacent villages. Significantly fewer An. koliensis dispersed. Unfed mosquitoes suffered a high pre-release mortality but had a similar oviposition cycle to those which were released blood-fed, suggesting that they did not experience any difficulty in obtaining a blood meal.

The effectiveness of mosquito coils containing esbiothrin under laboratory and field conditions.

Tests were made to correlate the chemical content of mosquito coils with the knockdown and bite-inhibitory action of the smoke in the laboratory and with the protective effect in field use. Smoke from a blank coil, containing no pyrethroid, gave no knockdown, 10% inhibition of biting in the laboratory using Aedes aegypti, and 39% protection in field tests in village huts on the Kenyan coast with a mixed population of mosquitoes including 71% Anopheles gambiae. Coils containing low experimental contents of 0.044% and 0.099% Esbiothrin, an isomer blend rich in the D-allethrolone ester of D-trans-chrysanthemic acid, gave rapid knockdown in both small chamber and 25 m3 room tests, and 71% and 94% inhibition of biting respectively in the laboratory. In the field they gave 74% and 84% protection from mosquitoes alighting. Chemical content was therefore a good guide to knockdown and bite inhibition in the laboratory and also to the considerable protection found in the field.