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Biomedical subjects

C A Maxwell

Publications and source records attributed to C A Maxwell.

At least 19 recordsLinked to original sources
PubMed2006

Comparison of coverage with insecticide-treated nets in a Tanzanian town and villages where nets and insecticide are either marketed or provided free of charge.

BACKGROUND: There is much emphasis on social marketing as a means of scaling up coverage with insecticide-treated nets and the question has arisen whether nets provided free-of-charge will be looked after by householders. METHODS: Over several years questionnaires and surveys of usage and condition of nets were carried out throughout a town and 15 villages in north-east Tanzania, where nets and insecticide have to be purchased and in 24 other villages where over 15000 nets had been donated and annual re-treatment is provided free-of-charge. RESULTS: There was very high population coverage in the town but, in the villages where nets have to be purchased, only 9.3% of people used nets which were intact and/or had been insecticide-treated and could, therefore, provide protection. However, where nets had been provided free, over 90% of the nets were still present and were brought for re-treatment several years later. CONCLUSION: In this part of Tanzania, social marketing has performed well in a town but very poorly in villages. However, the study showed that people look after and bring for re-treatment nets which had been provided free-of-charge.

Adolescent↗
PubMed2006

Insecticide-treated bed-nets for malaria mosquito control.

Pyrethroid-treated bed-nets act against late-night biting mosquitoes, like traps baited by the body odor of the occupant. The personal protective effect of treated nets is considerable, even if they are torn. However, some biting of the occupants does occur, as shown by matching microsatellite alleles in mosquito blood meals to those of net occupants. When whole communities were provided with treated nets, ovarian age grading showed that mosquito survival was reduced, and so was the number of sporozoite-positive mosquitoes in malarious communities. Thus, a high percentage of coverage of all members of malaria-endemic communities is considered to be the most effective way of providing protection for highly malaria-vulnerable children and pregnant women. Teams distributing nets or retreating them free of charge show high productivity, and we consider this the most cost-effective way to proceed. There is evidence for reduced anti-malaria antibody levels in children in communities where treated nets have long been used. However, overall benefits in reduced anemia and mortality are sustained. A high frequency of the kdr resistance gene has not prevented pyrethroid-treated nets from functioning, but it is important to develop alternative fabric treatments in case stronger forms of resistance emerge.

Africa↗
PubMed2006

Tests of Olyset nets by bioassay and in experimental huts.

BACKGROUND: Olyset nets are a type of long-lasting insecticidal net made of polyethylene fibre with permethrin incorporated into it and with a 4 mm mesh size. BIOASSAYS: Olyset netting was wrapped around a wire frame and the mosquitoes were released inside for bioassays. There was significantly faster knockdown and higher percent mortality than bioassays with the netting attached to a WHO cone with a piece of cardboard on the other side of the net to prevent escapes through the large mesh. It is suggested that with the latter method some mosquitoes place their tarsae through the mesh on to the cardboard, thus avoiding insecticide contact. TRIALS IN EXPERIMENTAL HUTS: Four mm mesh nets were compared with conventional 1.5 mm mesh nets treated with permethrin. In further trials in huts Olyset nets which were either unwashed or five times washed, with or without subsequent heating, and a Olyset net which had been in domestic use for four years or a new Olyset net were compared with a net treated with bifenthrin. RESULTS & CONCLUSION: In all cases Anopheles biting on sleepers under the nets was reduced and Anopheles mortality was increased by the use of the insecticidal nets. No significant impact of washing or heating was detected and an Olyset net was as good as new after four years use, but did not cause as much mosquito mortality as bifenthrin treated nets.

Animals↗
PubMed2002

Mutations in dhfr in Plasmodium falciparum infections selected by chlorproguanil-dapsone treatment.

Treatment with the novel antifolate drug combination chlorproguanil-dapsone effectively cleared asymptomatic Plasmodium falciparum infections in 246 (93.5%) of 263 children in the Usambara Mountains of Tanzania during the course of a 2-week follow-up. Samples from 71 recurrent infections, collected over a 9-week follow-up, showed selection for parasites with the triple mutant Ile(51)-Arg(59)-Asn(108) in dihydrofolate reductase. There was no selection for mutations in dihydropteroate synthetase, the target enzyme of dapsone. Search for complete identity in the highly polymorphic genes coding for merozoite surface proteins 1 and 2 in parasite samples collected before and after treatment indicated that the majority of recurrent parasitemias were new infections. These observations on selection in Tanzania and the lack of selection reported from a less endemic area suggest that the active metabolite of chlorproguanil, which has a short half-life in the blood, may persist in the liver, where it exerts selective pressure on growing preerythrocytic stages.

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

Hyaluronic acid skin fillers: adverse reactions and skin testing.

BACKGROUND: Hyaluronic acid (HA) fillers have been proposed as alternatives to other temporary skin fillers, such as bovine collagen, for treating facial skin lines and for providing lip augmentation. Several types of commercial HA fillers are now available in many countries. They include Restylane, which is produced by microbiologic engineering techniques, and Hylaform, which is HA extract derived from rooster combs. They have been approved for use in several countries, but not currently in the United States. There are no recommendations to perform pretreatment skin testing by the manufacturers. OBJECTIVE: Our purpose is to describe and comment on our experiences with Hylaform and Restylane fillers. Observation of any side effects and skin testing results were documented. METHODS: Between September 1996 and September 2000, 709 patients were treated with Hylaform and Restylane and were followed up clinically for at least 1 year. Three of these patients (0.42%) developed delayed skin reactions. Three other patients were referred for evaluation of their skin reactions from other practitioners. Five of these 6 patients agreed to skin testing of their forearms. RESULTS: In the 5 patients tested, challenge intradermal skin testing was positive in 4 patients; the reactions started approximately 8 weeks after injection. CONCLUSIONS: There was a slight incidence of delayed inflammatory skin reactions to two HA fillers. Both of these reactions occurred after the first and repeat injections. Challenge skin testing was positive in 4 of 5 tested patients.

Biocompatible Materials↗
PubMed2001

The integration of tissue structure and nuclear function.

Living cells can filter the same set of biochemical signals to produce different functional outcomes depending on the deformation of the cell. It has been suggested that the cell may be "hard-wired" such that external forces can mediate internal nuclear changes through the modification of established, balanced, internal cytoskeletal tensions. This review will discuss the potential of subnuclear structures and nuclear chromatin to participate in or respond to transduction of mechanical signals originating outside the nucleus. The mechanical interactions of intranuclear structure with the nuclear lamina will be examined. The nuclear lamina, in turn, provides a structural link between the nucleus and the cytoplasmic and cortical cytoskeleton. These mechanical couplings may provide a basis for regulating gene expression through changes in cell shape.

Cell Nucleus↗
PubMed2000

Increased control of the sheep biting louse Bovicola (Damalinia) ovis with deltamethrin formulated in a fractionated wool grease carrier.

The synthetic pyrethroid deltamethrin (DM) containing a trace of [(14)C]-DM was formulated with non-oxidised sterol and wax ester fractions (F1) of wool grease and as the commercial preparation 'Clout-S'. These were applied as a 'backline' strip to sheep immediately after shearing and the concentration of [(14)C]-DM at meridians adjacent to the application strip and at 1/4 and 3/4 of the dorsal-ventral distance was determined. The F1 formulation resulted in significantly greater lateral spread of DM with less remaining at the application site (66+/-8% of dose) 98 days after treatment compared to 'Clout-S' (94+/-3% dose). Autoradiographic examination of treated wool demonstrated that there was more DM in the lower half of the wool staple when formulated in F1 compared to 'Clout-S'. Greater mortality occurred when sheep biting lice Bovicola (Damalinia) ovis were exposed in vitro to wool containing DM from F1 compared to 'Clout-S' treated sheep. In field trials there was increased efficacy against synthetic pyrethroid resistant B. ovis with F1 formulation than with 'Clout-S'. The study has demonstrated that synthetic pyrethroid availability, and therefore efficacy, can be significantly increased when the insecticide is formulated in a 'carrier' with the physicochemical characteristics of wool grease.

Animals↗
PubMed1999

Production and oxidation of wool grease after shearing.

OBJECTIVE: To measure the production and amount of oxidation of wool grease secreted immediately after shearing. To identify components of wool grease that might act as a carrier to facilitate lateral diffusion of topically applied insecticides. DESIGN: Fine-wool Merino sheep were shorn and residual greasy wool was collected from the sheep's flank. The quantity of grease produced, and the amount of oxidation was measured during 18 days after shearing. Wool grease was fractionated into five component groups based on their polarity and the degree of oxidation in these fractions determined. RESULTS: There was a 24% increase in grease production within 2 days after shearing but secretions returned to pre-shearing amounts after 4 days. During this period wool grease oxidized rapidly. Of the grease fractions examined, sterol and wax esters remained essentially unoxidized whereas free sterols such as cholesterol and lanosterol, fatty acids and polar lipids, aldehydes and alcohols were extensively oxidized within 7 days after shearing. CONCLUSION: The transient increase in grease production after shearing may facilitate diffusion of topically applied synthetic pyrethroid insecticides. Oxidation of grease components may then contain the insecticide and limit further diffusion. Incorporating the insecticide in non-oxidising fractions of wool grease may make insecticide dispersion more efficient.

Administration, Cutaneous↗
PubMed1999

Can vector control play a useful supplementary role against bancroftian filariasis?

A single campaign of mass treatment for bancroftian filariasis with diethylcarbamazine (DEC) in Makunduchi, a town in Zanzibar, United Republic of Tanzania, combined with elimination of mosquito breeding in pit latrines with polystyrene beads was followed by a progressive decline over a 5-year period in the microfilarial rate from 49% to 3%. Evidence that vector control had contributed to this long-term decline was obtained by comparison with another town, Moga, where a DEC campaign was used without vector control and where resurgence of microfilariae could be observed 3-6 years after the campaign. In Zanzibar town, treatment of 3844 wet pit latrines and cesspits with polystyrene beads reduced the adult mosquito population in houses by about 65%. Supplementary treatment of open drains and marshes with Bacillus sphaericus produced little or no additional reduction compared to a sector of the town where only pit treatment with polystyrene was carried out. The cost and effort of achieving the 65% reduction in mosquito population could hardly be justified for its impact on filariasis alone, but its noticeable impact on biting nuisance might help to gain community support for an integrated programme.

Animals↗
PubMed1999

Studies on anti-folate antimalarials in east Africa.

Chlorproguanil-dapsone (CD) appears to be a promising anti-folate combination (Amukoye et al., 1997) to substitute for pyrimethamine-sulfadoxine (PS), which has a long half-life and against which there is resistance in several Plasmodium falciparum populations including the highly endemic lowland area near Muheza, Tanzania (Trigg et al., 1997).

Africa, Eastern↗
PubMed1999

Biological problems with the replacement of a vector population by Plasmodium-refractory mosquitoes.

Attempts are being made to backcross into Anopheles gambiae s.s. the gene(s) which cause zoophily in Anopheles quadriannulatus. Such a backcrossed strain might be preferable to a Plasmodium-refractory strain as a basis for genetic control because a refractory strain could select for evasion of refractoriness in the wild Plasmodium population. The species composition of the malaria vector population in several Tanzanian villages was overwhelmingly An. gambiae s.s. in a normal rainy season, but consisted of four species, all proved by ELISA and/or PCR to carry P. falciparum sporozoites, at the time of the heavy rains associated with El Niño. Thus any scheme, for malaria transmission control by replacement of vectors by genetically-manipulated non-vectors, would have to be able to replace more than one species.

Animals↗
PubMed1998

A comparison of use of a pyrethroid either for house spraying or for bednet treatment against malaria vectors.

In an intensely malarious area in north-east Tanzania, microencapsulated lambdacyhalothrin was used in four villages for treatment of bednets (provided free of charge) and in another four villages the same insecticide was used for house spraying. Another four villages received neither intervention until the end of the trial but were monitored as controls. Bioassays showed prolonged persistence of the insecticidal residues. Light traps and ELISA testing showed reduction of the malaria vector populations and the sporozoite rates, leading to a reduction of about 90% in the entomological inoculation rate as a result of each treatment. Collections of blood fed mosquitoes showed no diversion from biting humans to biting animals. Incidence of re-infection was measured by weekly monitoring of cohorts of 60 children per village, after clearing preexisting infection with chlorproguanil-dapsone. The vector control was associated with a reduction in probability of re-infection per child per week by 54-62%, with no significant difference between the two vector control methods. Cross-sectional surveys for fever, parasitaemia, haemoglobin and weight showed association of high parasitaemia with fever and anaemia and beneficial effects of each intervention in reducing anaemia. However, passive surveillance by resident health assistants showed no evidence for reduced prevalence of fever or parasitaemia. Net treatment consumed only about one sixth as much insecticide as house spraying and it was concluded that the former intervention would work out cheaper and nets were actively demanded by the villagers, whereas spraying was only passively assented to.

Bedding and Linens↗