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Biomedical subjects

C F Curtis

Publications and source records attributed to C F Curtis.

At least 91 records · Page 5Linked to original sources
PubMed1995

Village trial of bednets impregnated with wash-resistant permethrin compared with other pyrethroid formulations.

A village-scale field trial of pyrethroid-impregnated mosquito nets was undertaken in The Gambia, West Africa, in the Mandinka village of Saruja (13 degrees 13'N, 14 degrees 55'W) during July-November 1989. Nearly all the villagers possessed and used their own bednets. Anopheles gambiae is the main vector of human malaria in the area. An experimental wash-resistant formulation of permethrin was compared with standard emulsifiable concentrate (EC) formulations of permethrin and lambda-cyhalothrin, versus placebo-treated bednets. Target concentrations of pyrethroids on bednets were permethrin 500 mg/m2 and lambda-cyhalothrin 25 mg/m2. The experimental design involved random allocation of a treatment to one net per family. Whereas 68% of people questioned said they washed their nets fortnightly, observations during the 16-week trial period showed that only 4/130 (3%) of nets involved in the trial had been washed as frequently as once per month. Early morning searches for mosquitoes under bednets (1 day/week for 16 weeks) found significantly more mosquitoes (60% An.gambiae) in placebo-treated nets than in pyrethroid-treated nets. The numbers found with each of the three pyrethroid treatments did not differ significantly from each other. Insecticidal efficacy of the treatments was tested by bioassays using wild-caught unfed mosquitoes exposed to netting for 3 min. Linear regression analysis of bioassay mortality against number of times that a net had been washed by villagers showed that nets impregnated with the wash-resistant permethrin retained their insecticidal properties better than nets impregnated with lambda-cyhalothrin or with the standard permethrin formulation.

Animals↗
PubMed1995

Anopheles arabiensis and An. gambiae chromosomal inversion polymorphism, feeding and resting behaviour in relation to insecticide house-spraying in Tanzania.

Differential responses of the mosquitoes Anopheles arabiensis and An. gambiae sensu stricto to house-spraying with DDT or lambda-cyhalothrin were evaluated in relation to chromosomal inversion polymorphism, feeding and resting behaviour of these malaria vectors in Tanzania. Blood-fed mosquitoes from pit traps outdoors, exit traps on windows and indoor-resting catches were identified cytogenetically and the chromosomal inversion frequencies compared between samples and species. Their outdoor-resting behaviour was assessed by a mark-release-recapture experiment and by determining the proportion of freshly blood-fed individuals in exit traps. The source of bloodmeals was analysed by an ELISA method. Endophagic females of An. arabiensis were more likely than those of An.gambiae to exit from a house on the night of blood-feeding. Only in one out of three villages was there evidence that chromosomally distinct individuals within a species had different preferences for resting sites. There were indications, but not conclusive evidence, that mosquitoes caught indoors or outdoors had a tendency to return to the same type of resting site. In villages sprayed with either insecticide, the mean age of the vector populations was greatly reduced, compared with those in the unsprayed villages. An.arabiensis females exited from DDT sprayed houses after blood-feeding, whereas with lambda-cyhalothrin those exiting were mostly unfed and there was a decline in the human blood index. The excitorepellency of DDT was perceived as a disadvantage, whereas lambda-cyhalothrin apparently had more impact on malaria transmission by An.arabiensis.

Animals↗
PubMed1995

Canine eosinophilic folliculitis and furunculosis in three cases.

The historical, clinical and histopathological features of three dogs with eosinophilic folliculitis and furunculosis are described. The disease was characterised by the rapid development of pruritic, papular, pustular and ulcerative lesions on the dorsum of the muzzle. Skin lesions were confined to the face in two cases. The third dog had more generalised pustular lesions. Skin biopsy specimens showed marked eosinophil infiltration particularly centred on pilosebaceous units. Dermal collagen necrosis was evident in two cases. Similar facial lesions have previously been described as 'nasal pyoderma'. The three dogs failed to respond to initial antibacterial therapy but showed a rapid clinical response when prednisolone was given orally at doses ranging from 1 to 2.2 mg/kg, in addition to the antibacterial therapy, suggesting that glucocorticoids are indicated for the treatment of eosinophilic folliculitis and furunculosis. The aetiology of the disease was not determined.

Administration, Oral↗
PubMed1995

Test for association of DDT resistance with inversion polymorphism in Anopheles arabiensis from Ethiopia.

Association of DDT resistance levels with chromosome inversion polymorphism was investigated in Anopheles arabiensis samples collected from southwestern Ethiopia. The frequencies of the 2Ra, 2Rd, and 3Ra inversions in 1988 and 1990 between the DDT survivors pooled from the 3 times of exposure and unexposed controls did not differ significantly. However, for 2Rb a significant association was observed (Mantel-Haenszel chi 2, stratified for year of collection = 10.4, P < 0.001). The inversion frequency was 56% among unexposed individuals, but it was 64-92% among those surviving exposure.

Animals↗
PubMed1995

Deltamethrin impregnated bednets against Anopheles minimus transmitted malaria in Assam, India.

Of the 20 Anopheles species caught in villages in Sonapur, Assam, only An. minimus was incriminated as a malaria vector by finding sporozoites in the salivary glands. It was found to be endophagic and endophilic in Assam and because its biting peaked after midnight it was a suitable target for insecticide impregnated bednets. After the withdrawal of DDT spraying and collecting a year's baseline data, deltamethrin impregnated nets were distributed in 3 villages, untreated nets were distributed in 6 villages and 3 were held as untreated controls. The population of each of these groups of villages was about 1700. The nets were well received by the local tribal population. Human landing catches with baits unprotected or under partially lifted nets showed that the nets provided a high degree of personal protection against all the local species of human biting mosquito. In addition, there was evidence for suppression of the An. minimus population in a village with treated nets. Malaria was monitored by weekly active surveillance in all the villages. In the untreated control villages the slide positivity rate and monthly parasite index rose significantly during the trial. In the villages with untreated nets, these parameters showed no significant change, but in the villages with treated nets they declined significantly. On the basis of these results, the widespread distribution of impregnated nets was recommended to the state health authorities.

Animals↗
PubMed1994

Mortality of under-fives in a rural area of holoendemic malaria transmission.

From January 1992 to December 1993, a total of 361 births and 243 deaths were recorded by village reporters in five villages in Muheza District, north eastern Tanzania. Among those aged less than one year 48 deaths were recorded, giving an infant mortality rate of 133 per 1000 live births (95% CI 97.9-168.0). There were 42 deaths among the censused population of 845 children aged 1-4 years (24.8/1000/year, 95% CI: 17.4-32.3). Verbal autopsy questionnaires were administered to parents or close relatives of 83 of the dead infants and children. From analysis of these, 30 of the deaths were tentatively attributed to malaria. The results are discussed in relation to other studies in East and West Africa and to the prospects for reducing mortality by use of insecticide impregnated bednets.

Adolescent↗
PubMed1994

Host choice of anopheline mosquitoes in a malaria endemic area of western Venezuela.

Bloodmeals of exophilic anopheline mosquitoes collected resting on vegetation in a malaria endemic area in western Venezuela were identified by ELISA. Using a TMB peroxidase substrate in the ELISA, human bloodmeals were readily identified up to 40 h after ingestion in all laboratory-fed mosquitoes tested. Assay sensitivity declined to 75% identifiable 44 h post-feeding. The Human Blood Index and the Feeding Index of each species differed between the three villages studied. An.triannulatus was generally more anthropophilic than An.nuneztovari and An.oswaldoi. These contrasting results emphasize the difficulties of interpreting host choice data.

Animals↗
PubMed1994

Detection of pyrethroid resistance in Anopheles mosquitos.

Although pyrethroid insecticides are a promising means of controlling Anopheles malaria vectors, there is a need to monitor for resistance. It has been proposed that the results of the WHO-recommended testing method, involving exposure to impregnated paper for 1 hour, might be misleading because of knockdown during this period, and that exposure to a higher dose of pyrethroid for 2 minutes might be preferable. However, comparative tests with a susceptible and a permethrin-resistant strain of A. stephensi showed that exposure for 1 hour was at least as sensitive in detecting resistance as was the short exposure method.

Animals↗
PubMed1994

Laboratory studies of pyrethroid-netting combinations to kill mosquitoes.

Bioassays of cotton or synthetic netting, impregnated with one of two formulations of deltamethrin or a formulation of lambda-cyhalothrin, showed that the order of merit of these insecticides varied significantly with the type of netting used. Washing reduced the insecticidal power of all combinations of insecticide and netting. Halving the time of exposure and doubling the dose tended to increase the mortality. Different An. stephensi strains varied significantly in susceptibility. Netting (5 to 8 mm mesh) impregnated with deltamethrin was effective in killing mosquitoes which penetrated the netting in search of an animal host.

Analysis of Variance↗
PubMed1993

The effects of house spraying with DDT or lambda-cyhalothrin against Anopheles arabiensis on measures of malarial morbidity in children in Tanzania.

The effects of house spraying of DDT and lambda-cyhalothrin against populations of Anopheles arabiensis were assessed in children aged between 1 and 10 years with regard to fever episodes and parasite prevalences. DDT and lambda-cyhalothrin treatment did not reduce the prevalence of malaria episodes as defined by fever (temperatures > or = 37.4 degrees C and/or fever reported) combined with high parasitaemia (> or = 100 parasites/200 leucocytes). However, the prevalence of malaria parasitaemia, of the episodes of fever with any level of malaria parasitaemia and of high parasitaemia alone were significantly reduced. Furthermore, the reduction in mean parasite densities was greater in children of the 1-2 years age group for both insecticides and also for children of 3-5 years age group with lambda-cyhalothrin. Measured and/or reported fever and high parasitaemia were correlated and the data indicated that most of the fevers in these children could be attributed to malaria. Using this criterion it is concluded that the population of An. arabiensis responded to both DDT and lambda-cyhalothrin house spraying which in turn also reduced malaria-related morbidity.

Age Factors↗
PubMed1993

Malaria in travellers: epidemiology and prevention.

Malaria continues to be a serious health risk for travellers. The malaria parasites which infect humans can only be naturally transmitted by female mosquitoes of the genus Anopheles. Travellers to malaria endemic areas require detailed advice on appropriate chemoprophylaxis against malaria and personal protection against mosquito bites. The decision on an appropriate chemoprophylaxis or standby therapy regimen should reflect the malaria risk, pattern of drug resistance, and the toxicity of available drugs. Currently travellers encounter a number of problems in protecting themselves against malaria. Advice is often both inadequate and inaccurate; and all the recommended drug regimens are associated with minor, and occasionally major adverse reactions. Because of poor compliance to drug prophylaxis and to reduce the impact of drug resistance, protection against mosquitoes has a critical role in protecting travellers from malaria. Compliance to methods of personal protection not only reduces the malaria risk but also limits the nuisance and loss of sleep from biting insects.

Antimalarials↗
PubMed1993

Analysis of mosquito bloodmeals by DNA profiling.

Human specific genetic markers have been used to profile the human DNA found within a mosquito bloodmeal. In this technique, variable numbers of tandem repeat (VNTR) sequences are employed to prime amplification of human DNA in the polymerase chain reaction (PCR) and the radiolabelled products are analysed by high resolution denaturing gel electrophoresis. Matching of DNA profiles allows identification of the individual human host. Bloodmeals of 125 female Anopheles gambiae Giles mosquitoes, caught dead or alive in verandah-trap huts wherein two people had slept overnight protected by intact insecticide-impregnated bednets, were analysed: thirty-five out of thirty-nine profiles generated were identical to those of the sleepers under the nets. Thus the blood-fed mosquitoes found after impregnated nets have been used cannot, in most cases, be explained away by entry of already fed mosquitoes into the huts.

Animals↗
PubMed1992

Malaria entomological inoculation rates in western Venezuela.

Over 61,000 anophelines collected between January 1988 and October 1989 in three villages in western Venezuela were assayed by ELISA for Plasmodium vivax circumsporozoite (CS) protein. The six specimens confirmed positive belonged to three species: Anopheles (Nyssorhynchus) nuneztovari Gabaldón, 1940, A. albitarsis Arribalzaga, 1878 sensu lato and A. oswaldoi (Peryassu, 1922). The estimated CS protein rate for all species combined was 0.01% (95% confidence limits 0.004-0.02%). This CS protein rate and the mean number of bites received by the collectors indicated a sporozoite inoculation rate of about 10.5 infective bites per person per year. From this value and the number of human malaria cases reported it was estimated that only 0.32% of bites by CS-positive mosquitoes led to a malaria infection. The CS protein rate is so low that this parameter would not be a practical indicator of the efficacy of control campaigns in this area.

Animals↗
PubMed1992

The use of PCR to help quantify the protection provided by impregnated bednets.

Bednets impregnated with a pyrethroid insecticide are an important recent advance in malaria vector control. Here, Suzanne Gokool, Deborah Smith and Chris Curtis describe how a combination of field work with specially designed huts and DNA fingerprinting of mosquito bloodmeals can be used to help assess whether impregnated bednets would give sufficient protection to prevent infection in areas of intense malaria transmission.

Journal Article↗
PubMed1992

Biting and resting behaviour of anophelines in western Venezuela and implications for control of malaria transmission.

A study was conducted in three villages in western Venezuela between February 1988 and October 1989 to determine the biting and resting activity of anophelines in relation to human habits, rainfall and fenitrothion spraying of houses. Mosquitoes were collected landing on humans inside and outside experimental huts throughout the night. Only three mosquitoes were found resting in the huts in the morning, but 2470 were collected resting on vegetation in the early morning. The collections yielded eleven species of anopheline, the most abundant being Anopheles nuneztovari, comprising over 75% of the total anophelines collected, followed by An.triannulatus, An.albitarsis s.l. and An.oswaldoi. The four most abundant species showed different diel patterns of biting. For An.nuneztovari the peak of activity was close to midnight indoors and outdoors, for An.triannulatus between 19.00 and 20.00 hours outdoors, for An.albitarsis mainly before midnight indoors and outdoors and for An.oswaldoi outdoors at 19.00 hours, with an additional smaller peak indoors at midnight. Most of the human population use bednets, go to bed before 22.00 hours and are therefore most exposed to mosquitoes that bite outdoors early in the night. Fenitrothion house-spraying failed to prevent large mosquito populations developing in the wet season, presumably because of their exophilic resting habits. The possible advantages of impregnation of existing bednets with pyrethroids, and provision of nets for people who do not have them, are discussed.

Animals↗