Progress in malaria vector control.

Malaria control, except in tropical Africa, will probably continue to be based to a large extent on the use of insecticides for many years. However, the development of resistance to insecticides in the vectors has caused serious difficulties and it is necessary to change the strategy of insecticide use to maximize their efficacy. A thorough knowledge of the ecology and behaviour of each vector species is required before the control strategy can be adapted to different epidemiological situations. The behavioural differences between sibling species have been recognized for several years, but study of this problem has recently been simplified by improved means of identification that involve chromosomal banding patterns and electrophoretic analysis. Behavioural differences have also been associated with certain chromosomal rearrangements.New records of insecticide resistance among anophelines continue to appear and the impact of this on antimalaria operations has been seriously felt in Central America (multi-resistance in Anopheles albimanus), Turkey (A. sacharovi), India and several Asian countries (A. culicifacies and A. stephensi), and some other countries. Work continues on the screening and testing of newer insecticides that can be used as alternatives, but DDT, malathion, temephos, fenitrothion, and propoxur continue to be used as the main insecticides in many malaria control projects. The search for simpler and innovative approaches to insecticide application also continues.Biological control of vectors is receiving increased attention, as it could become an important component of integrated vector control strategies, and most progress has been made with the spore-forming bacterium, serotype H-14 of Bacillus thuringiensis. Larvivorous fish such as Gambusia spp. and Poecilia spp. continue to be used in some programmes.Application of environmental management measures, such as source reduction, source elimination, flushing of drainage and irrigation channels, and intermittent irrigation have been re-examined and currently a great deal of interest is being shown in these approaches.There has been limited interest in the genetic control of mosquitos and the phenomenon of refractoriness in some strains of the disease vectors, with the idea of replacing the vector species with the refractory strain. More research is needed before this approach can become a practical tool.It is apparent that in future a more integrated approach will have to be used for vector control within the context of antimalaria programmes. Training of staff, research, and cooperation at all levels will be an essential requirement for this approach.

A multidisciplinary study on bancroftian filariasis in Jakarta.

A study on bancroftian filariasis in Jakarta has indicated that one person in one year could be exposed to 223,000 bites of Culex pipens fatigans and to 1,941 infective-stage larvae of Wuchereria bancrofti. Blood surveys with 20 mm3 samples revealed a microfilaria rate of 6%. Although some cases of hydrocele (4% of 272 males examined) were found, there was little evidence of severe filarial disease in either males or females. Amongst wild-caught mosquitoes only 0.3% contained infective larvae, but much higher levels of vectorial competence were established under laboratory conditions. High daily vector mortality (30%) coupled with noticeable improvements in standards of living could have been important factors preventing an increase in endemicity.

Observations on the breeding habitats of Aedes aegypti (L.) in Jakarta, Indonesia.

A one-year study was done of the breeding habitats of Aedes aegypti (L.) and of the water storage habits of the inhabitants in four crowded districts of urban Jakarta. Immature mosquitoes were found in or near houses in containers of relatively clean water used for drinking or bathing purposes. An average of 185 containers were found per 100 houses, of which 60 were positive for Aedes immatures, resulting in a Container Index of 32%. The mean potential water storage capacity per house was 173 liters of which only 92 liters of water was actually being stored at any one time. Water jars were the most common containers found, but bak mandi (cuboidal or oblong concrete reservoirs) held more water per container. Total water storage per house in bak mandi was twice that of water jars and ten times that of drums, which were uncommon. Ant traps and other miscellaneous containers were unimportant for either water storage or mosquito production. A mean of 0.93 pupae per house was found, pupal production indoors being ten times than outdoors. Indoor water jars produced more pupae per house than all other containers combined. The infestation rate of covered containers was significantly higher than that of uncovered containers, perhaps because loose-fitting lids allowed entrance of gravid females to the attractive darkened interior of the container.

Studies on filariasis in the Pacific. 4. The application of the membrane filter concentration technique to a survey of Wuchereria bancrofti filariasis in Kepu district, Jakarta, Indonesia.

A blood survey for filariasis was carried out in the Kepu District of Jakarta. Examination of stained 20 c.mm finger-prick blood thick films and membrane filter concentration (MFC) of 1 ml venous blood. The youngest age group examined, 5-9 years old revealed a mf rate of 17% of which 71% were of a low density character detected by MFC only. The mf rate appears to remain relatively constant from the 10-14 year old group onward, approximately 35%, but at all age groups at least half the infections were of low density. The highest mf rate and density was observed present in the 15-20 year old group.

A large-scale field trial of ultra-low-volume fenitrothion applied by a portable mist blower for the control of Aedes aegypti.

Long-term control of Aedes aegypti, the vector of dengue haemorrhagic fever in Thailand, was obtained by 2 thorough applications of fenitrothion mist applied at a target dosage rate of 0.1 ml per m(3) of room space. Perfect control lasted for 6-7 months after treatment and densities were substantially reduced for up to a year after treatment. Recovery of the population was still slow up to almost 16 months after treatment. This degree of control was achieved by the immediate mortalities produced by 2 treatments spaced about 2 weeks apart, the larvicidal effect of the fenitrothion aerosol, and a limited residual effect that prevented oviposition for a period, so that the recovery potential was greatly diminished. It appears that aerosol and mist treatments designed as epidemic control measures can be adapted to long-term preventive control of A. aegypti. However, the equipment used and the method of application require further improvement.

Sequential application of ultra-low-volume ground aerosols of fenitrothion for sustained control of Aedes aegypti.

A trial was carried out of the efficacy of fenitrothion ultra-low-volume aerosol applied by vehicle-mounted cold aerosol generator for the control of Aedes aegypti. Five applications of fenitrothion at intervals of 11-49 days at dosages of 511-1 095 ml/ha gave sustained control for 4-5 months in an area of some 14 ha containing 1 300 houses. Immediate killing of adult mosquitos and some larvicidal effect interrupted oviposition and retarded the recovery of the mosquito population. Sequential treatments applied in advance can evidently suppress the population throughout the rainy season, when epidemics of dengue haemorrhagic fever occur, and have operational advantages over larvicidal treatment. The Culex pipiens fatigans population was suppressed for only a few days after each treatment.