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At least 1,207 records · Page 67Linked to original sources
PubMed1987

Epidemiological aspects of an outbreak of dengue fever/dengue haemorrhagic fever in Singapore.

A nation-wide outbreak of 260 cases of DF/DHF with 1 death occurred in Singapore from Apr-Sept 1986. The outbreak originated from 3 separate foci of transmission at the western, south-eastern and north-eastern parts of the island and then spread to other dengue receptive urban and suburban areas. The morbidity rate was highest in young male Chinese adults between 15 and 24 years of age. The outbreak was rapidly brought under control through destruction of adult Aedes mosquitoes, surveys and source reduction of larval breeding habitats, health education and to a certain extent law enforcement. The Aedes population was high in the main foci of transmission although the overall house index was only 1.1. Other factors which could have precipitated the outbreak included waning herd immunity of the human population and continuous introduction of dengue virus into the country.

Aedes↗
PubMed1981

Issues in filariasis--a century of enquiry and a century of failure.

A great deal is known about the biology of the filarial parasites infecting man and of their transmission, their clinical manifestations, their treatment and their control but many more people are infected with Bancroftian filariasis and onchocerciasis today than more than 100 years ago when Manson discovered the first live cycle. There has been some success in the control of the Simulium vectors of onchocerciasis in parts of Africa and mass chemotherapy has helped to reduce Bancroftian filariasis in a few Pacific Islands but the main endemic areas have seen no benefit from all the advance in the techniques for controlling these diseases. There is an obvious need for more research to find better tools that are less hazardous to the environment and more acceptable to the affected communities. Fortunately the combined resources of the United Nations Development Programme, the World Bank for Development and the World Health Organization in the setting up of the Special Programme for Research and Training in Tropical Diseases has stimulated a renewed interest in these problems. An obvious area for further research is on the epidemiology of the disease with special emphasis on transmission of the parasites to help with the development of predictive models which might assist in the design and evaluation of control programmes. There is a need for novel approaches to kill the vectors and for the development of more effective and less hazardous drugs. There is a need for immunologists to try to produce vaccines which will help to consolidate other methods of control but of more immediate values will be the production of more specific immunological diagnostic tests and methods for modifying the immunopathology processes caused by the disease and accentuated by treatment. But whatever new tools are produced it is still true to say that control measures will be effective only if there is active cooperation by the affected communities. It is therefore essential that laboratory research is supplemented with research on human behaviour in relation to the transmission of the diseases and also on the acceptability of control measures if we are to avoid the disappointments of many other antiparasitic control campaigns.

Animals↗
PubMed1996

An operational perspective on measuring aerosol cloud dynamics.

Three areas are discussed in this paper: 1) U.S. Air Force Reserve/USDA bioassays to determine the effective swath width of ultra-low volume (ULV) aerial applications conducted with the C-130 Modular Aerial Spray System (MASS), 2) the use of aerial spray computer models to predict spray offset distance and their use as a substitute for field testing, and 3) a demonstration on an aerial spray expert system called ASPEX being developed at the U.S. Air Force Reserve Aerial Spray Branch.

Animals↗
PubMed1994

[Status of insecticide resistance in 4 strains of Musca domestica collected in animal farms].

Resistance to insecticides made from different chemical compounds were studied in 4 strains of Musca domestica collected from 2 poultry farms and 2 cow farms following WHO methodology. A high resistance to malathion was observed (resistance factor values ranging from 102X to 252X), and moderate, to diazinon, fenthion, dichlorvos, DDT, and propoxur. Resistance to the deltametrine and permethrin pyreturins was not observed.

Animal Husbandry↗
PubMed1998

Disinfectant/antiparasitic activities of Jatropha curcas.

OBJECTIVE: To investigate the disinfectant/antiparasitic activities of Jatropha curcas as a first step in providing a cheap, readily available disinfectant and malaria vector control agent. DESIGN: Bacteriological and parasitologic tests were carried out on laboratory bench surfaces using the sap and crushed leaves of Jatropha curcas. Four rectangular areas labelled A, B, C and D were first swabbed and streaked onto McConkey and Nutrient agar plates. Section A was treated with "Hibiscrub", D with exterma germcloth, B and C with full strength sap and leaf extracts respectively. Effect of the sap was also tested on helminth ova, vector control on mosquito eggs and toxic effects of the sap on mice. SETTING: The study was carried out in the medical microbiology laboratory of the College of Medicine, University of Lagos, Lagos. RESULTS: Observation showed that the sap extracted germicidal actions on the growth of common bacteria of Staphylococcus, Bacillus and Micrococcus species on contact and retained such effects on treated laboratory bench surface for close to six hours after initial application. Ova of Ascaris Lumbricoides and Necator americanus incubated in 50% and 100 concentrations of the sap at room temperature showed either no evidence of embryonation after 21 days in the case of A. Lumbricoides, negation of hatchability in hookworm, or complete distortion in both. The sap also exhibited strong inhibitory effect on normal larval growth of mosquito, but was highly toxic to mice when administered through oral or intraperitoneal routes. CONCLUSION: J. curcas would provide a very cheap, readily available disinfectant and malaria vector control agent and should be commercially exploited.

Animals↗
PubMed1999

Control of zoophilic malaria vectors by applying pyrethroid insecticides to cattle.

The principal method of malaria control in South and West Asia--indoor residual spraying--is extravagant with insecticide. A more efficient way of deploying insecticide might be to apply it on livestock since the malaria vectors in the region are highly zoophilic. A series of investigations assessed the potential of cattle treated with pyrethroid to control zoophilic mosquitoes. Permethrin, deltamethrin, and lambdacyhalothrin were applied to cattle using a sponge at concentrations of 0.5 g/m2, 0.025 g/m2, and 0.025 g/m2, respectively. 'Whole animal' insecticide bioassays that simulated natural mosquito-host contact were used to measure insecticidal and behavioural effects on wild host-seeking mosquitoes. The bioassays were performed on both sheltered and outdoor grazing animals for up to 45 days post-treatment. The possibility that treatments might cause diversion of host-seeking vectors from cattle to people nearby was also investigated. At the doses tested deltamethrin had the most pronounced and longest-lasting effect, reducing the proportion of bloodfed survivors by over 50% for the first two weeks. The majority of mosquitoes affected by the insecticide were killed before feeding. Insecticidal impact was generally lower on grazing than on sheltered animals. There was no diversion of host-seeking mosquitoes from treated cattle to nearby humans at any stage after treatment. The application of insecticide to livestock using a campaign approach may prove an effective means of controlling malaria in the region. At the doses tested deltamethrin is the most appropriate insecticide for this purpose.

Administration, Topical↗
PubMed1964

THE MONOFACTORIAL INHERITANCE OF RESISTANCE TO DIELDRIN IN LARVAL AND ADULT CULEX QUINQUEFASCIATUS SAY.

A susceptible and a resistant strain were isolated from an originally heterogeneous laboratory colony of Culex quinquefasciatus Say (= Culex pipiens fatigans Wiedemann) by use of discriminating concentrations of dieldrin on fourth-instar larvae. By cross-breeding, hybrids of intermediate susceptibility were obtained. By repeated cross-breeding and elimination of susceptibles the authors have shown that resistance to dieldrin is controlled by a single inheritable factor which is neither fully recessive nor dominant in the hybrid genotype, since the ratios of the LC(50) values were 1:19:196. Cross-resistance was shown to lindane but not to malathion or to any of three carbamates.Similar tests were made with adult females exposed to papers impregnated with n-dioctyl phthalate as solvent to secure high concentrations of dieldrin. Resistance in this stage also was neither fully recessive nor dominant, but it can be calculated quantitatively only for the hydrid (approximately 15-fold) since longer exposure was required with the resistant genotype. Determination of dieldrin pick-up showed that this cannot account for the differences in susceptibility of the genotypes. Analysis of resistant females surviving exposure to dieldrin papers showed slow loss of dieldrin and thus added confirmation to the hypothesis that metabolism is not the controlling process in dieldrin-resistance.

Animals↗
PubMed1964

THE SIGNIFICANCE OF DDT-IRRITABILITY TESTS ON MOSQUITOS: WITH AN ANNEX ON RESULTS OBTAINED WITH THE IRRITABILITY TEST METHOD RECOMMENDED BY THE WHO EXPERT COMMITTEE ON INSECTICIDES.

The author reviews various laboratory investigations of the effects of insecticides on mosquito behaviour. The only extensive data on this subject concern the effects of DDT on irritability. The measurement of this response is discussed, and information is collated on the factors affecting it, such as the type and state of the insecticide, the species and physiological state of the mosquito and environmental factors including temperature, humidity, light and crowding. The author concludes that, despite the numerous difficulties associated with this subject, a sound technique (such as that recommended by the WHO Expert Committee on Insecticides) should be adequate to detect inherent differences in irritability between mosquito colonies, of a magnitude likely to be important in practice.An annex describes tests carried out by the author on strains of two anopheline and four culicine species with the irritability test method recommended by the WHO Expert Committee on Insecticides. Four DDT-resistant strains were less irritated by DDT than normal colonies, the difference being significant in the two culicine resistant strains.

Animals↗
PubMed2004

A comparison of two spray nozzle systems used to aerially apply the ultra-low-volume adulticide fenthion.

Field experiments with the mosquito adulticide fenthion (Baytex) compared the conventional flat-fan nozzle system (Tee Jet 8002SS) and a new high-pressure hollow-cone nozzle system (1/8 MISS). Ground deposition and aerial flux of the mosquito adulticide fenthion were measured up to 4.83 km downwind by using filter paper and yarn collectors, respectively. Biological efficacy was investigated by using caged salt-marsh mosquitoes (Ochlerotatus taeniorhynchus), and caged fiddler crabs (Uca pugilator) were exposed to quantify nontarget impact. Peak deposits to the ground were 1,729 microg/m2 and 240 microg/m2 for the flat-fan nozzles and high-pressure cones, respectively. Deposits from the flat-fan nozzles resulted in a cumulative fiddler crab mortality of 80%, whereas no deaths were recorded with the high-pressure system. The range of fenthion flux detected in the air when using the yarn collectors was similar for the 2 systems, with both showing drift through 4.83 km. For the flat-fan spray nozzle system, the aerosol flux ranged from 3.02 to 67.33 microg/yarn collector. The range of aerosol flux for the high-pressure nozzle spray system was 0.15-50.66 microg/yarn collector. Although the 2 systems produced comparable ranges of flux, the high-pressure system provided higher control efficacy against mosquitoes. Maximum mosquito control when using the flat-fan spray nozzle system against female salt-marsh mosquitoes was 26.6%, whereas maximum control with the high-pressure spray system was 92.9%.

Aerosols↗
PubMed2000

Epidemiology in the strategies for malaria control.

A rapid overview is presented of the evolution of the main orientations of malaria control, since the discovery of mosquito transmission. Stated control objectives appear to have oscillated between expectations to eradicate the vector, or at least the disease, and more modest approaches to minimise the effects of the infection. High optimism was raised when a new control measure, or new combination of existing measures, appeared to be highly effective and was expected to have universal applicability. The implementation of large scale campaigns eventually found the limits of applicability of the proposed strategy and the exaggerated expectations soon gave way to disillusion and, eventually, to a revival of research. The longest and most impacting period of exaggerated expectations was the global malaria eradication campaign of the 1950s and 1960s, which completely disregarded the study of local epidemiology, considering that all it was needed was to know if an area was "malarious" or not. Research was practically abandoned and, even when reinstated after the recognised failure of the campaign, it has retained an almost exclusive orientation towards the development of control tools, drugs or eventually vaccines. One of the earliest victims of the eradication campaign was the study of epidemic malaria and its determinants in different epidemic prone areas. In spite of an extremely long period of disillusion, lasting for almost two decades, the reality of the malaria problem led WHO and member countries to agree on a global strategy of control, aiming at a realistic use of existing tools, to at least reduce or prevent mortality. An essential element of this strategy is the prevention or control of malaria epidemics and the selective use of vector control, both of which have to be based on a solid knowledge of local epidemiology, the study of which has to rejoin the path abandoned fifty years ago.

Animals↗