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Biomedical subjects

C F Curtis

Publications and source records attributed to C F Curtis.

At least 109 records · Page 6Linked to original sources
PubMed1992

Various pyrethroids on bednets and curtains.

Verandah trap huts in a Tanzanian village were used to assess the effectiveness of impregnated bednets and curtains in preventing hut entry and feeding by, and in killing of, Anopheles gambiae and An. funestus. Permethrin, deltamethrin, lambdacyhalothrin and pyrethrum were used for impregnation of damaged or undamaged bednets, sisal eaves curtains or bed curtains made of polypropylene fibre. The performance of the three synthetic pyrethroids did not differ statistically significantly, except that on a damaged net permethrin was better at preventing feeding. Sisal eaves curtains deterred mosquitoes from hut entry but did not kill those that had entered. In assessing damaged nets and curtains it must be recognised that anything less than the best vector control may have no appreciable impact on holoendemic malaria.

Animals↗
PubMed1992

Evaluation of different methods of catching anopheline mosquitoes in western Venezuela.

During a longitudinal study of vector biology and malaria transmission in western Venezuela, adult mosquitoes were collected by different methods and their efficiency was compared with human landing catches. CDC light traps, a double-net, a calf-baited trap and collection of resting mosquitoes on vegetation were tested. These methods did not prove to be effective substitutes for human landing catches.

Animals↗
PubMed1991

Trial of pyrethroid impregnated bednets in an area of Tanzania holoendemic for malaria. Part 3. Effects on the prevalence of malaria parasitaemia and fever.

Children aged 1-10 in five villages were contacted fortnightly. Their axillary temperatures, reports of fevers and blood slides were taken. Following the introduction of permethrin impregnated nets into two estate villages the slide positivity for falciparum malaria declined markedly. In traditional villages the introduction of impregnated nets had less convincing effects than in the estate villages and DDT spraying had no perceptible effect on malaria. Over all villages there was a clear relationship between axillary temperature greater than 37.4 degrees C, reports of fever and high parasitaemia. We defined malaria fever in this way, and found in some cases significant reductions in occurrence of such fever following some time after introduction of permethrin impregnated nets. No such effects were found with lambdacyhalothrin nets or with DDT spraying.

Bedding and Linens↗
PubMed1991

Trial of pyrethroid impregnated bednets in an area of Tanzania holoendemic for malaria. Part 4. Effects on incidence of malaria infection.

Groups of about 30 children in each of five villages were given pyrimethamine-sulfadoxine to clear their malaria parasitaemia, and they were followed up with fortnightly blood slides. Parasitaemia returned rapidly in the absence of vector control, but more slowly when pyrethroid impregnated nets were in use or the houses had been sprayed with DDT. Variation between the incidence of malaria infection in these cases seemed to depend more on ecological or social factors than on the particular form of vector control adopted.

Bedding and Linens↗
PubMed1991

Trial of pyrethroid impregnated bednets in an area of Tanzania holoendemic for malaria. Part 1. Operational methods and acceptability.

In five Tanzanian villages, nets impregnated with permethrin or lambdacyhalothrin were given out. The people received them enthusiastically and brought their nets for re-impregnation at six monthly intervals. Bioassays showed that the insecticidal power of permethrin impregnated nets remained adequate for six months unless the nets were washed. Nets with 30 mg lambdacyhalothrin/m2 retained high insecticidal power despite washing, but this dose caused temporary cold-like symptoms in those sleeping under freshly treated dry nets. Methods by which durable bednets might be made affordable by Tanzanian villagers are discussed.

Animals↗
PubMed1991

Trial of pyrethroid impregnated bednets in an area of Tanzania holoendemic for malaria. Part 2. Effects on the malaria vector population.

The malaria vector population consisted mainly of Anopheles gambiae s.s. with a small contribution from An. funestus and An. rivulorum. The mosquitoes coming to bite in bedrooms were monitored with light traps set beside untreated bednets. When impregnated bednets were provided for all the other beds in a village the Anopheles populations declined but the Culex quinquefasciatus populations were unaffected. The survival of An. gambiae (as measured by the mean number of ovarian dilatations) and the sporozoite rate declined following introduction of the nets and the estimated sporozoite inoculation rates into people not under their nets declined by more than 90%. The net introductions caused sharp declines in the number of mosquitoes resting indoors, but the evidence was inconclusive regarding diversion to outdoor resting, animal biting, earlier biting or outdoor biting. DDT spraying greatly reduced the Anopheles populations.

Animals↗
PubMed1990

The effects of chloroquine on the infectivity of chloroquine-sensitive and -resistant populations of Plasmodium yoelii nigeriensis to mosquitoes.

Subtherapeutic doses of chloroquine have been reported to enhance infectivity of drug-resistant Plasmodium species to their vectors. In this investigation, Plasmodium yoelii nigeriensis N67 strain showed enhanced infectivity to mosquitoes when stimulated by chloroquine. Both sensitive and resistant clones were derived from the N67 strain by dilution, showing that this strain is polymorphic for the resistant trait. A resistant subline was derived by selection under drug pressure from a chloroquine-sensitive clone, but neither the sensitive nor the resistant clones or sublines showed enhancement of infectivity in the presence of chloroquine. This suggests that the enhancement of infectivity shown by the N67 strain is a response to chloroquine stimulation shown only by certain of the genotypes within it, and that this response to chloroquine is not a trait causally connected with the genes coding for chloroquine resistance.

Animals↗
PubMed1990

Amplification and analysis of human DNA present in mosquito bloodmeals.

DNA fingerprinting should permit the identification of individual human hosts of haematophagous arthropods, providing epidemiologically useful information, for example, the biting rates on different people and the impact of insecticide-impregnated bednets. Investigations reported here demonstrate that it is possible to extract, amplify and fingerprint human DNA from the bloodmeals of individual female Anopheles gambiae mosquitoes kept at 24 degrees C for up to 10-15 h post-ingestion.

Animals↗
PubMed1989

Permethrin-impregnated bednets: behavioural and killing effects on mosquitoes.

Permethrin-treated pieces of netting and simulated bednets were evaluated against Anopheles gambiae Giles and Aedes aegypti (L.) in the laboratory. When female mosquitoes were allowed to feed on a human arm through pieces of impregnated netting fastened at the end of tubes, doses above 2 g/m2 were required to stop blood-feeding of both An. gambiae and Ae. aegypti. A much lower dose prevented Ae. aegypti from feeding on mice through impregnated netting. When mosquitoes were released in a room and a human subject sat under a permethrin-impregnated (0.2 g/m2) bednet with an arm pressed against the net (mesh 1.5 mm), mosquitoes failed to bite through the net. All the mosquitoes trying to bite through or entering the net through holes cut in it were knocked down within 30 min of release and ultimately died. Permethrin-impregnated wide-mesh (4 or 8 mm) bednets similarly prevented entry and caused high mortality-rates of An. gambiae.

Aedes↗
PubMed1989

Recent research on impregnated mosquito nets.

The present status of impregnated mosquito nets and other impregnated materials is discussed. Research projects which have produced most of the publications on this subject were conducted in areas in Africa with relatively high endemicity of malaria. In these areas, usage of impregnated mosquito nets caused substantial reductions in the sporozoite inoculation rates and some reduction in incidence of malaria attacks. However, there was little or no reduction in parasite rates in the human population. In several countries in Asia and the Pacific, vector control with impregnated mosquito nets has been introduced on a large scale, thus proving its affordability and compatibility with local customs in these countries. Substantial reductions in malaria parasite rates have been obtained in areas with low levels of malaria transmission. In order to develop the vector control method which is most appropriate for each area, much more research is needed on the technical and organizational aspects of vector control with impregnated mosquito nets. Examples are given of data already available as well as an indication of gaps in knowledge which still exist and will need more attention.

Bedding and Linens↗
PubMed1988

Methods for replacement of malaria vector populations.

The prospects are reviewed of replacement of malaria vector populations by harmless mosquito populations by means of: (i) ecologically competitive non-vector species; (ii) natural selection due to the harmfulness of being infected; (iii) selection for insecticide resistance genes; (iv) meiotic drive; (v) negative heterosis; and (vi) hybrid dysgenesis. Serious difficulties exist with all of these approaches. At present 'dilution', i.e. release of insects carrying the desired genes without any system for forcing population replacement is the only available method. It avoids the disadvantage that, in constructing elaborate genetic 'packages', factors for low fitness may be irreversibly incorporated into them. It is debatable whether release of males only or both sexes should be attempted.

Animals↗
PubMed1987

Experimental hut trials of permethrin-impregnated mosquito nets and eave curtains against malaria vectors in Tanzania.

Permethrin impregnated netting was tested against Tanzanian populations of Anopheles arabiensis Patton, An.gambiae Giles and An.funestus Giles in experimental huts fitted with traps to catch samples of the mosquitoes existing during the night. Treated bednets killed some mosquitoes and increased the tendency of survivors to exit during the night. Treated cotton did not perform so well as treated nylon bednets. An impregnated bednet in which holes had been cut, to simulate a torn net, reduced the number of mosquitoes which fed and survived approximately as well as an intact untreated net. Treated curtains around the eaves of experimental huts did not perform so well as bednets but caused considerable reductions in the number of mosquitoes which fed and survived. However, there was no such effect when treated netting was placed around the eaves of a dwelling house. When one child slept under a treated net and another slept outside the net in the same hut, the number of bites on the latter child was less than if neither child had been under a net. Various aspects of the applicability of permethrin impregnated nets on a community basis are discussed.

Animals↗
PubMed1987

The relative efficacy of repellents against mosquito vectors of disease.

Laboratory tests of insect repellents by various different methods showed that An.stephensi Liston was consistently more susceptible than An.gambiae Giles, An.albimanus Wiedemann or An.pulcherrimus Theobald. The six repellents tested were di-ethyl toluamide (deet), di-methyl phthalate (DMP), ethyl-hexanediol, permethrin, citronella and cedarwood oil. Testing systems in which the mosquitoes were presented with a choice gave consistently lower ED50 values than when there was no choice, i.e. the standards of tolerance are not absolute but depend on the options available. In field tests in an experimental hut a curtain with a high dose of di-ethyl toluamide (deet) reduced biting in the hut but had to be re-impregnated frequently. Deet-impregnated anklets gave about 84% protection against Culex quinquefasciatus Say for 80 days after one impregnation, in a trial in which the anklets were brought out of sealed storage and tested for 2 h nightly. Similar protection was found against An.funestus Giles but the protection against An.gambiae s.l., An. coustani Laveran and Mansonia spp. was not as good. There were highly significant differences between the four collectors' mosquito attractiveness but this varied highly significantly between the mosquito species.

Animals↗
PubMed1987

Egg-float ridge number in Anopheles stephensi: ecological variation and genetic analysis.

Eight Indian laboratory stocks of Anopheles stephensi Liston could be grouped into three categories with, respectively, 14-22, 12-17 and 9-15 ridges on the egg-floats. The mode number of ridges among the eggs laid by individual females in these stocks was 16-19, 13-16 and 10-14, respectively. The category with the highest egg-float ridge number corresponded with the type-form and the lowest with var. mysorensis Sweet and Rao; the new egg-float category with ridge number modes of thirteen to sixteen was designated as 'intermediate'. All three forms, i.e. type-form, intermediate and myosorensis were observed in semi-urban areas while only intermediate and mysorensis were seen in rural areas. Breeding experiments indicated no post-copulatory barriers between the populations. Likelihood analysis of the results of crosses and back crosses indicated that variation in ridge number is controlled by more than one genetic factor. The stocks with different ridge numbers are best considered as 'ecological variants'.

Animals↗
PubMed1986

A simple model of the build-up of resistance to mixtures of anti-malarial drugs.

In an organism with a life-cycle modelled on that of Plasmodium two separate resistance genes are assumed, each protecting against one of two unrelated drugs. The model was used to compare the rates of build-up of resistance in a population where the two drugs are used either as a mixture or in sequence. The model suggests that the use of a mixture would be advantageous if: both resistances are initially rare; there is recombination between the genes; a large proportion of the parasite population is unexposed to the drugs.

Animals↗