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Biomedical subjects

C F Curtis

Publications and source records attributed to C F Curtis.

At least 37 records · Page 2Linked to original sources
PubMed2002

Laboratory and field comparisons of pyriproxyfen, polystyrene beads and other larvicidal methods against malaria vectors in Sri Lanka.

Hand-dug gem pits are important breeding sites for larvae of malaria vectors in Sri Lanka. Therefore, studies were carried out to help to select an effective, economic and convenient method that could be used to control malaria vector mosquito breeding in gem pits in a mining area. The effectiveness of four types of floating layers of polystyrene was compared in the laboratory and it was found that 2 mm expanded beads were the most effective for suffocating Anopheles larvae and pupae. The insect growth regulator, pyriproxyfen at dosages of 0.01 and 0.1 mg/l were tested in the laboratory and complete inhibition of emergence was found at both concentrations. A small-scale field trial was carried out for over a year to assess the efficacy of two concentrations of pyriproxyfen, 2 mm diameter expanded polystyrene beads, temephos, used engine oil and filling pits with soil. Pyriproxyfen only required re-application twice a year, whereas temephos or oil require 12 applications per year. Due to re-excavation by gem miners, polystyrene beads and filling of pits were not as permanent solutions as was expected. Calculations based on all available data showed that two annual treatments with pyriproxyfen at 0.01 mg/l would be the most cost-effective method with oil only slightly more expensive. However, the reduced required frequency for visiting every pit made the pyriproxyfen method the one of choice. The same low concentration of pyriproxyfen also effectively inhibited emergence of adults from river-bed pools.

Animals↗
PubMed2002

Comparative insecticidal power of three pyrethroids on netting.

Adult mosquitoes, Anopheles gambiae Giles and Culex quinquefasciatus Say (Diptera: Culicidae), were exposed for 3 min to replicate samples of polyester netting cut from replicate bednets treated with pyrethroid insecticide formulations at the recommended concentration (alphacypermethrin SC at 40mg ai/m2; cyfluthrin EW at 50 mg ai/m2; deltamethrin WT at 25 mg ai/m2), or treated with only a quarter of those dosages. After 4 months domestic use of the bednets in Malawi, chemical assays showed that pyrethroid deposits on the netting were somewhat less than the target concentrations. Comparing the pyrethroid bioassay results with Anopheles at both treatment concentrations, deltamethrin gave significantly higher mortality (99.7-100%) than the other compounds (alphacypermethrin 94-96%, cyfluthrin 80-89%). Culex bioassay mortality was lower (alphacypermethrin 56-74%; cyfluthrin 63-65%; deltamethrin 50-81 %) and results with the three pyrethroid insecticides at their recommended doses did not differ significantly.

Animals↗
PubMed2002

Pyrethroid resistance in tropical bedbugs, Cimex hemipterus, associated with use of treated bednets.

When Tanzanian villages were provided with pyrethroid-treated bednets, bedbugs (Cimicidae) disappeared; however, after about 6 years they have re-appeared in these villages. Using a newly devised test-kit, susceptibility tests of bedbugs Cimex hemipterus (Fabricius) from five of these villages showed that there is resistance to permethrin and alphacypermethrin in bedbugs from each of the villages, in contrast to those from five villages without treated nets. Circumstantial evidence indicates that bedbug resistance to pyrethroid insecticides may evolve more readily in villages with incomplete coverage rates of treated bednets, allowing bedbug infestations to become re-established. Bedbugs have not returned to a village where nearly all the beds have been provided with pyrethroid-treated bednets for 14 years.

Animals↗
PubMed2002

Effect of community-wide use of insecticide-treated nets for 3-4 years on malarial morbidity in Tanzania.

OBJECTIVES: To investigate (1) benefits due to personal protection of individual net users vs. mass killing of mosquitoes within villages as a result of widespread net usage; (2) sustainability over several years of benefits against malarial morbidity of insecticide-treated nets; (3) distribution of the benefits in different age groups of children and (4) whether, as a result of fading immunity, older age groups 'paid for' the benefits which they had enjoyed when younger. METHODS: (1) Tabulation of earlier data to compare personal and community-wide effects against mosquito vectors; (2) two cross-sectional surveys for malaria parasitaemia, malarial fever, anaemia and splenomegaly in children in eight Tanzanian villages, in which there had been community-wide use of bednets which had been annually re-treated with alphacypermethrin for 3-4 years; (3) comparison between children of different age groups and with intact, torn or no nets in these villages and in 4-6 villages without nets. RESULTS: A 90-95% reduction in infective bites outside nets in netted villages and an additional 54-82% reduction of bites among individual net users. Highly significant reductions (by 55-75%) in malarial morbidity for children aged 6 months to 2 years were found in netted villages with, for some outcomes, better results among individuals who themselves had intact treated nets. For older children, benefits were less clear or absent, but there was no sign that the benefits early in life were 'paid for' by worse outcomes in the netted villages later in childhood. CONCLUSIONS: The overall benefits to the community of widespread use of treated nets are sustainable and are not reversed in 3-4 years as a result of fading immunity. It is important to ensure high enough coverage to realize the full potential of the treated net method. By showing an impact on the vector population in the community these results provide a strong argument for organized free provision of net treatment, rather than relying on marketing.

Anemia↗
PubMed2002

Use of floating layers of polystyrene beads to control populations of the filaria vector Culex quinquefasciatus.

Floating layers of polystyrene beads suffocate mosquito larvae and pupae and inhibit egg laying. The layers are very durable in breeding sites with water contained within walls, as in wet pit latrines and soakage pits. In some areas such pits constitute an important breeding site for Culex quinquefasciatus. Trials have been conducted in communities in Zanzibar, Tanzania, and in Tamil Nadu, India, where such mosquito populations were the vectors of Wuchereria bancrofti. In each case, treatment of all the pits with polystyrene beads was integrated with mass treatment of the people with antifilarial drugs-in Zanzibar in 1988 with diethylcarbamazine (DEC) and in India in the 1990s with DEC plus ivermectin. The results were compared with those in communities with the mass drug treatment alone and with control communities with neither treatment. The polystyrene-bead treatments greatly and sustainably reduced the vector populations. Comparison of the communities after drug treatment ceased showed that this form of vector control contributed markedly to the prevention of a resurgence of filarial infection. Where Cx. quinquefasciatus breeding in pits form a major component of the vector population, use of polystyrene-bead layers could assist considerably in the process of eliminating lymphatic filariasis by mass drug administration.

Animals↗
PubMed2001

Control of malaria vectors with the insect growth regulator pyriproxyfen in a gem-mining area in Sri Lanka.

The study was conducted in eight adjacent villages in central Sri Lanka where there are many shallow pits dug by gem miners that fill with water. These become breeding places of the main malarial vector Anopheles culicifacies, and of the second most important vector Anopheles subpictus, but not of Anopheles varuna, the third most important vector. With the help of local volunteers, data on the adult populations of these three species was collected by various standard methods, and data on the incidence of malaria cases was collected by two clinics set up for the project and through the existing hospitals. Prevalence of malaria infection in symptom-less people was investigated by mass blood surveys. On the basis of a year's pre-intervention data the villages were stratified into four with high levels of malaria transmission and four with lower transmission. Within each stratum two villages were randomly assigned for mosquito control by treating all the gem pits, as well as river bed pools, with a granular formulation of the insect growth regulator pyriproxyfen at a target dose of 0.01 mg a.i./litre. The intervention caused significant reductions in the adult populations of An. culicifacies and An. subpictus. Similarly, incidence of malaria was reduced in the intervention villages to about 24% (95% c.l. 20-29%) of that in the controls. Prevalence of parasitaemia also declined significantly. It is concluded that in this situation where, with active community participation, the breeding sites of the main vectors could be located; vector control by a highly active and persistent insect growth regulator can be a very effective means of malaria control.

Adolescent↗
PubMed2001

Evaluation of a commercially available enzyme-linked immunosorbent assay for the diagnosis of canine sarcoptic mange.

This study was designed to assess the accuracy of a commercial enzyme-linked immunosorbent assay for the diagnosis of canine scabies. Serum samples from 37 dogs were examined blind; 12 had sarcoptic mange confirmed by the identification of mites in skin scrapings, 12 were atopic (with positive intradermal reactions to one or more aeroallergens, including Dermatophagoides farinae), and 13 were healthy dogs with no history of skin disease. Optical density values of more than 0.16 were considered positive, 0.145 to 0.16 were considered questionable and less than 0.145 were considered negative. Ten of the 12 dogs with scabies were positive, all 12 atopic dogs were negative, and 11 of the 13 healthy dogs were negative and two were questionable.

Animals↗
PubMed2001

Unexpected anthropophagic behaviour in Anopheles quadriannulatus.

The strongly anthropophilic behaviour of Anopheles gambiae Giles sensu stricto (Diptera: Culicidae), the most important malaria vector in Africa, has been demonstrated by field and laboratory studies. Other members of the An. gambiae complex express varied degrees of anthropophily. Anopheles quadriannulatus (Theobald) species A and B are more zoophilic members of the complex and hence are considered to be of no medical importance. Olfactometer experiments with An. quadriannulatus species A have demonstrated attraction to both human and cow odour. To extend these olfactometer observations a choice experiment was conducted in an outdoor cage with a human and a calf as baits, using laboratory-reared mosquitoes. Anopheles gambiae s.s. (from Liberia) and two strains of An. quadriannulatus species A (SKUQUA from South Africa, SANGQUA from Zimbabwe), marked with different coloured fluorescent powders for identification purposes, were released simultaneously and given an equal opportunity to feed on either host. The experiment was repeated six times. Bloodmeals were identified using the precipitin technique. Anopheles gambiae s.s. showed highly anthropophagic behaviour, taking 88% of bloodmeals from the human host. In contrast, both strains of An. quadriannulatus fed with equal frequency on the human or the calf; the response to either host was not significantly different. These results confirm the olfactometer findings and demonstrate anthropophagic behaviour not previously recorded in this species. This finding has implications for prospective manipulation of host preference for genetic control purposes.

Animals↗
PubMed2001

Diagnostic techniques and sample collection.

With the advancing knowledge of medicine, diagnostic techniques and laboratory equipment, practicing veterinary surgeons are increasingly capable of processing many of their patients' blood, urine, and tissue samples on-site. No case is better suited to this scenario than the dermatology case, which enjoys a unique privilege in the clinic because the clinician is frequently able to harvest, process, and analyze pathologic samples from affected animals during or shortly after the consultation, eliminating the need to wait for results from external laboratories and consequently reducing the time to recovery. Good sampling techniques are crucial for the acquisition of optimal data however, and this article highlights the key points of these procedures and recommends when they are best employed.

Animals↗
PubMed2001

Differential behaviour of Anopheles gambiae sensu stricto (Diptera: Culicidae) to human and cow odours in the laboratory.

A dual port olfactometer was used to study the response of Anopheles gambiae Giles sensu stricto to odours of human and animal origin. Human odour consisted of human skin emanations collected on a nylon stocking, which was worn for 24 h. This was tested alone or together with 4.5% carbon dioxide, the concentration in human and cattle breath. Cattle odours consisted of cow skin emanations and/or carbon dioxide. Cow skin emanations were collected by tying a nylon stocking ('cow sock') around the hind leg of a cow for 12 h. Anopheles gambiae s.s. was consistently highly attracted by human odour, which is consistent with the high degree of anthropophily in this mosquito. Anopheles gambiae s.s. was not attracted by human or cattle equivalent volumes of carbon dioxide and this gas did not enhance the effect of human skin residues. Furthermore, A. gambiae s.s. showed a high degree of aversion to cow odour. When human odour and cow odour were tested together in the same port, mosquitoes were still highly attracted, indicating that whilst cattle odour may deter A. gambiae s.s., these mosquitoes can detect human odour in the presence of cattle odour. It was concluded that carbon dioxide plays a minor role in the host seeking behaviour of A. gambiae s.s., whilst host specific cues such as human skin residues play a major role and very effectively demonstrated anthropophilic behaviour in the laboratory.

Animals↗
PubMed2000

Infectious disease. The case for deemphasizing genomics in malaria control.

Solving the enormous problem of malaria worldwide will require a balance between investments in research and control. In this point-counterpoint, two scientists describe the rationales for these very different strategies. Steve Hoffman believes that genomics research is the best investment in the future if we have the vision of malaria eradication. Chris Curtis presents an opposing viewpoint, that low-tech control approaches are the practical ones under current conditions.

Animals↗
PubMed2000

Should DDT be banned by international treaty?

The insecticide DDT has been an effective and affordable means of malaria control in many countries, but pressure for its use to be banned is mounting. Here, Chris Curtis and Jo Lines take a critical look at evidence that links house spraying by DDT with harm to the environment and human health, and stress the need for resources for alternatives to DDT to be made available to countries that would be affected by a DDT ban.

Animals↗