Comparative efficacies of permethrin-, deltamethrin- and alpha-cypermethrin-treated nets, against Anopheles arabiensis and Culex quinquefasciatus in northern Tanzania.

Mosquito nets treated with permethrin, deltamethrin or alpha-cypermethrin at 25 mg/m(2) were evaluated in experimental huts in an area of rice irrigation near Moshi, in northern Tanzania. The nets were deliberately holed to resemble worn nets. The nets treated with permethrin offered the highest personal protection against Anopheles arabiensis (61.6% reduction in fed mosquitoes) and Culex quinquefasciatus (25.0%). Deltamethrin and alpha-cypermethrin provided lower personal protection against An. arabiensis (46.4% and 45.6%, respectively) and no such protection against Cx. quinquefasciatus. Permethrin performed poorly in terms of mosquito mortality, however, killing only 15.2% of the An. arabiensis and 9.2% of the Cx. quinquefasciatus exposed to the nets treated with this pyrethroid (after correcting for control mortality). The alpha-cypermethrin and deltamethrin performed marginally better, with respective mortalities of 32.8% and 33.0% for An. arabiensis and 19.4% and 18.9% for Cx quinquefasciatus. The poor killing effect of permethrin was confirmed in a second trial where a commercial, long-lasting insecticidal net based on this pyrethroid (Olyset) produced low mortalities in both An. arabiensis (11.8%) and Cx. quinquefasciatus (3.6%). Anopheles arabiensis survivors collected from the verandahs of the experimental huts and tested on 0.75%-permethrin and 0.05%-deltamethrin papers, in World Health Organization susceptibility kits, showed mortalities of 96% and 100%, respectively. The continued use of permethrin-treated nets is recommended for personal protection against An. arabiensis. In control programmes that aim to interrupt transmission of pathogens by mosquitoes and/or manage pyrethroid resistance in such vectors, a combination of a pyrethroid and another insecticide with greater killing effect should be considered.

Geometric approach to segmentation and protein localization in cell culture assays.

Cell-based fluorescence imaging assays are heterogeneous and require the collection of a large number of images for detailed quantitative analysis. Complexities arise as a result of variation in spatial nonuniformity, shape, overlapping compartments and scale (size). A new technique and methodology has been developed and tested for delineating subcellular morphology and partitioning overlapping compartments at multiple scales. This system is packaged as an integrated software platform for quantifying images that are obtained through fluorescence microscopy. Proposed methods are model based, leveraging geometric shape properties of subcellular compartments and corresponding protein localization. From the morphological perspective, convexity constraint is imposed to delineate and partition nuclear compartments. From the protein localization perspective, radial symmetry is imposed to localize punctate protein events at submicron resolution. Convexity constraint is imposed against boundary information, which are extracted through a combination of zero-crossing and gradient operator. If the convexity constraint fails for the boundary then positive curvature maxima are localized along the contour and the entire blob is partitioned into disjointed convex objects representing individual nuclear compartment, by enforcing geometric constraints. Nuclear compartments provide the context for protein localization, which may be diffuse or punctate. Punctate signal are localized through iterative voting and radial symmetries for improved reliability and robustness. The technique has been tested against 196 images that were generated to study centrosome abnormalities. Corresponding computed representations are compared against manual counts for validation.

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.

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.

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.

Insecticide treated nets: impact on vector populations and relevance of initial intensity of transmission and pyrethroid resistance.

Insecticide treated bednets locate a deposit of a quick-acting insecticide of low human toxicity between a sleeper and host-seeking mosquitoes. Thus a chemical barrier is added to the often incomplete physical barrier provided by the net. Treated nets may be considered as mosquito traps baited by the odour of the sleeper. Trials in Assam, Tanzania and elsewhere have shown that when a whole community is provided with treated nets, so many mosquitoes of anthropophilic species are killed by contact with the nets that the density and/or sporozoite rate of the vector population is reduced. In order to gain this "mass" or community effect, in addition to widespread personal protection, and thus to achieve the full potential of the treated net method, a high per cent coverage of the community is needed. This suggests that organised free provision of treated nets, comparable to a house spraying programme, is likely to be more cost-effective than trying to market nets and insecticide to very poor rural people. In areas with high malaria transmission, where acquisition of immunity to malaria is very important, it has been argued that vector control (without vector eradication) could, in the long run, make the situation worse by preventing the normal build-up of immunity. However, our data from Tanzania do not support this idea--3-4 years after provision of nets (which are re-treated annually) young children are still showing clear health benefits; older children are not "paying" for this by showing worse impact of malaria. There is less malaria morbidity in a highland area where malaria transmission is about 15x less intense than in a nearby lowland area. The per cent impact of treated nets malaria morbidity in both area was very similar. At present only pyrethroids are used for net treatment which suggested that emergence of pyrethroid resistance would have a disastrous effect. However, in West Africa, where there is now a high frequency of the kdr resistance gene in Anopheles gambiae, it is reported that treated nets continue to have a powerful impact on vector populations. In Tanzania, pyrethroid resistance has not been detected in malaria vectors, but it has emerged in bedbugs after seven years use of treated nets.

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.

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.

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.

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.

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.

A trial of proguanil-dapsone in comparison with sulfadoxine-pyrimethamine for the clearance of Plasmodium falciparum infections in Tanzania.

Considerable levels of resistance to sulfadoxine-pyrimethamine (SP) have been reported in Plasmodium falciparum in north-eastern Tanzania, and the identification of a suitable antimalarial to replace SP is now a high priority. We conducted a trial in July 2000 to determine the efficacy of proguanil (PG) plus dapsone (DS), compared with that of SP, for the treatment of asymptomatic falciparum infection. A total of 220 children with parasitaemia > or = 2000 per microL completed the study; 112 had received a single dose of SP (dosage calculated for pyrimethamine 1.25 mg/kg and sulfadoxine 25 mg/kg) and 108 had taken PG 10 mg/kg with DS 2.5 mg/kg each day for 3 days. Clearance of asexual parasites at day 7 was 14.3% with SP, but 93.5% with PG-DS. The remarkably high failure rate with SP was not associated with occurrence of leucine substitution at position 164 of the dhfr gene. Both treatment regimens were well tolerated. Compared with available data on another antifolate combination, chlorproguanil-dapsone ('Lapdap'), PG-DS was slightly but significantly inferior in achieving parasite clearance (99.5% versus 93.5%). The estimated cost of a 3-day course of PG-DS treatment for a child weighing 18 kg is US $0.15. With the rising incidence of SP-resistant P. falciparum infection, PG-DS could provide an effective, affordable and already available therapeutic alternative for malaria in East Africa at least until chlorproguanil-dapsone is registered.

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.

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.

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.

Comparison of bednets impregnated with different pyrethroids for their impact on mosquitoes and on re-infection with malaria after clearance of pre-existing infections with chlorproguanil-dapsone.

Comparisons of bednets treated either with alphacypermethrin or lambdacyhalothrin showed similar effectiveness by various entomological criteria. Lambdacyhalothrin was associated with significantly more reports of nasal irritation than alphacypermethrin. The 2 net treatments were equally effective in reducing incidence of new malaria infections and the treated nets were much more effective than untreated nets. These measurements were made after clearing existing infections with chlorproguanil-dapsone. This drug combination was more than 99% effective in clearing infections 1 week after treatment and a study of children taken to an altitude with no malaria transmission showed that there were very few recrudescences.

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.

PIP: With chemotherapy schedules for bancroftian filariasis having become far more convenient to use, the World Health Organization currently emphasizes chemotherapy against the disease, and vector control in only a supplementary role. Data are presented from studies conducted in urban areas of Zanzibar, Tanzania, where the vector of bancroftian filariasis is Culex quinquefasciatus, to determine whether sustainable vector control contributes usefully to the suppression of the disease and is feasible in different types of breeding sites without the use of organophosphorus insecticides. Data were obtained from a follow-up study conducted in the late 1980s in the highly filaria-endemic town of Makunduchi. A single campaign in early 1988 provided mass treatment of the population of 12,000 with diethylcarbamazine (DEC) at the dose of 72 mg/kg body weight. DEC treatment, together with the elimination of mosquito breeding in pit latrines using 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 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%. The 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.

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).

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.