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Malaria transmission is a multifactorial phenomenon. Climate is a major limiting factor in the spatial and temporal distribution of malaria, but many non-climatic factors may alter or override the effect of climate. Thirty years of monthly malaria incidence data from KwaZulu-Natal province, South Africa, reveal strong medium and long-term trends, which were not present in the climate data. This paper explores various non-climatic factors that may have contributed towards the observed trends. The development of antimalarial drug resistance, available information on human immunodeficiency virus (HIV) prevalence, cross-border people movements, agricultural activities, emergence of insecticide resistance and the case reporting system are reviewed and their potential effect on malaria transmission examined. Single-variable linear regression analysis showed significant association between seasonal case totals (log-transformed) and the measured level of drug resistance (log-transformed) (r2=0.558, n=10, P=0.013) as well as relative measures of HIV infection since 1990 (r2=0.846, n=11, P=0.001). The other factors appear to have affected the level of malaria transmission at certain periods and to some degree. The importance of surveillance and inclusion of non-climatic variables in analysis of malaria data is demonstrated.

Laser ablation ICP-MS is a powerful technique for the direct elemental analysis of solids with spatial resolution down to a few microns. However, its range of application is limited by the lack of calibration standards. This paper describes a novel approach to calibration that employs aqueous standards whose absorption coefficients are modified, by the addition of a chromophore, to produce the desired ablation yield. Chromophores for the important laser wavelengths at 193, 248 and 266 nm are given. The mechanism of ablation and parametric dependences for the modified aqueous standards were investigated and it was concluded that ablation proceeds by a three step process leading ultimately to nebulisation of the bulk liquid. This is important as such a process should not involve fractionation between elements. Calibration curves produced using the aqueous standards were linear and reproducible, but internal standardisation is required to provide linked calibration for real samples. NIST standard Reference Material 613 Trace Elements in Glass and low density polyethylene were analysed and the results agreed with reference values or those obtained by other techniques.

An approach to the assessment of fumes produced in laser material processing is presented. The subsequent design of the fume containment system and sampling strategy is detailed. Polyvinyl chloride (PVC) has been selected for investigation and the complexity resulting from the plethora of additives is discussed. Qualitative results from the preliminary studies of CO 2 laser cutting of PVC are presented together with an appraisal of the problems involved in extending this to quantitative analysis. Benzene, hydrogen chloride (HCl) and methyl methacrylate were found to be the dominant emissions.

To determine whether the re-introduction of DDT in KwaZulu-Natal had any effects on malaria transmission in the province.The 2000 malaria epidemic in KwaZulu-Natal has been attributed to pyrethroid-resistant anopheles mosquitoes in the area. Previous studies have shown that these mosquitoes are still susceptible to DDT. To determine whether DDT re-introduction had any impact on malaria transmission in KwaZulu-Natal, the following variables (pre- and post-epidemic) were investigated: (i) the number of reported cases; and (ii) the distribution of Anopheles funestus in relation to the insecticides sprayed.The notified malaria cases and the distribution of A. funestus were measured to determine the effects of DDT re-introduction on malaria transmission.After DDT re-introduction, the number of malaria cases decreased to levels lower than those recorded before the epidemic. A. funestus appears to have been eradicated from the province. The combination of an effective insecticide and effective antimalarial drugs in KwaZulu-Natal has resulted in a 91% decline in the malaria incidence rate. Unfortunately the continued exclusive use of DDT within the malarious areas of the province is threatened by the emergence of insecticide resistance.

The objective of this study was to produce data indicating whether insecticide-treated bednets should replace insecticide house spraying as a malaria control method in South Africa. We report 2 years of preliminary data on malaria incidence comparing areas receiving insecticide-treated bednets and those subjected to house spraying in northern KwaZulu-Natal.In order to measure significant reductions in malaria incidence between the two interventions, a geographical information system (GIS) was used to identify and create seven pairs of geographical blocks (areas) in the malaria high-risk areas of Ndumu and Makanis in Ingwavuma magisterial district, KwaZulu-Natal. Individual blocks were then randomly allocated to either insecticide-treated bednets or house spraying with deltamethrin. Malaria cases were either routinely recorded by surveillance agents at home or were reported to the nearest health facility.The results show that 2 years' use of insecticide-treated bednets by communities in Ndumu and Makanis, KwaZulu-Natal, significantly reduced the malaria incidence both in 1997 (rate ratio (RR) = 0.879, 95% confidence interval (CI) 0.80-0.95, P = 0.04) and in 1998 (RR = 0.667, CI 0.61-0.72, P = 0.0001). Using a t-test, these significant reductions were further confirmed by an assessment of the rate of change between 1996 and 1998, showing a 16% reduction in malaria incidence in blocks using treated bednets and an increase of 45% in sprayed areas (t = 2.534, P = 0.026 (12 df)). In order to decide whether bednets should replace house spraying in South Africa, we need more data on the efficacy of treated bednets, their long-term acceptability and the cost of the two interventions.

The nature of the fume generated by high power laser processing is dependent upon laser type, material being processed, assist gases used, and the energy density required to process the material. The fume produced from any one process will vary in its composition, aerosol size distribution, morphology, and toxicity, all of which are important factors when assessing human and environmental hazards. At present no straightforward method exists to estimate the hazards. In this article a method for indexing the hazards of fumes generated by laser materials processing is presented. The index can be applied to a wide range of materials and laser processing techniques and should lead to a standardization of information pertaining to laser-generated fumes. Two parameters are applied to describe the fumes hazard. The first parameter is the exposure limits, which indicates the perceived hazard of an individual component released during processing. The exposure limits used are the UK long-term occupational exposure s...

This paper outlines a brief historical perspective on malaria which is considered essential to an understanding of the gains made in the control of the disease, followed by an emphasis on the fact that control is a dynamic process requiring research back-up, private and public sector and national and international collaboration. Malaria control is based on scientific principles and ongoing success requires continual research input, government commitment to control of the disease and appropriately skilled and trained personnel. This overview cannot do justice to malaria control and research in South Africa in its entirety, but looks at some of the major factors facing malaria control that have motivated the Medical Research Council's research initiative, which includes vector and parasite research, the use of geographical information systems and the epidemiology of the disease, with a view to sustaining control in the future.

In March 1993, a study was undertaken in the Komatipoort/Malelane area to monitor the in vitro sensitivity of Plasmodium falciparum to antimalarial drugs currently in use in South Africa. Of the 12 isolates collected, 7 were successfully tested for sensitivity to chloroquine and quinine, 6 for mefloquine susceptibility, and 5 for sensitivity to Fansidar. Four of the isolates were resistant to chloroquine at RIII level, 1 at RII level, and 2 were sensitive. All isolates were found to be sensitive to both quinine and mefloquine. Results suggested possible resistance to Fansidar. These findings have implications for tourists travelling to this area.

There are several factors that support the need to assess the efficacy of potential alternative insecticides to DDT for malaria vector control. The objectives of this study were to evaluate the persistence and efficacy against Anopheles arabiensis of lambda-cyhalothrin used as an intradomiciliary insecticide in daub huts and to compare its efficacy in this regard to DDT. Exit trap catches showed the population of An. arabiensis was high during the months of January to March, with a peak in February. During all months, the number caught leaving lambda-cyhalothrin-sprayed huts was markedly less than the number from both control and DDT-sprayed huts. The percentage survival of bloodfed mosquitoes ranged from a low of 55% caught leaving the lambda-cyhalothrin-sprayed huts, to 82% of those caught leaving DDT-sprayed huts. The percentage of bloodfed mosquitoes caught leaving huts was high (60%). The survival of unfed mosquitoes was low, even from the control huts (43%).

Laboratory assessment of the residual efficacy of lambda-cyhalothrin (Icon) 10% AI against Anopheles arabiensis and Cimex lectularius was carried out. The insecticide was applied to daub substrates, simulating the wall surface of houses from 3 areas within the endemic malaria area of Natal, South Africa. Variability in residual efficacy was found between different areas and appeared to correlate to organic content of the substrate. Residual efficacy against An. arabiensis ranged from as little as 2 wk in some areas to in excess of 14 wk in others. Residual efficacy against C. lectularius was 4 wk for all 3 areas, but was 10 wk in only 2 areas.

What were first called simply false-positive Wassermann reactions and then lupus anticoagulant are now known as antiphospholipid or anticardiolipin antibodies (ACA). These are known to cause a tendency to thrombosis and are frequently present in many neurological conditions and infections. The pathological significance of these antibodies in acute infections, if any, is unknown. We investigated the presence of these antibodies in Plasmodium falciparum malaria in an endemic area in Natal/KwaZulu, and attempted to correlate the presence of this antibody with cerebral manifestations. Immunoglobulin G-anticardiolipin antibodies measured by enzyme-linked immunosorbent assay occurred significantly more frequently in 62 patients with acute Plasmodium falciparum malaria (33.9%) than in 37 control subjects (2.7%) (P0.0001). There was no significant difference in the mean parasite loads in those patients who were positive for ACA (1.75%) and those who were negative (1.59%) (P = 0.83). No correlation was found between parasite load and ACA levels in the patient group, or between the number of cerebral manifestations in patients with and without the antibody. The frequency of splenomegaly was not significantly different in patients with and without ACA (P = 0.06). We conclude that there is a high prevalence of ACA in acute falciparum malaria. The pathological significance of this antibody and its relationship to complications, especially cerebral ones, warrant greater attention and may improve the understanding of cerebral malaria and its management.

Plasmodium falciparum malaria is endemic in the northern KwaZulu areas of South Africa. The clinical morbidity produced by this parasite has not been studied since the institution of the present malaria control programme. Fifty-nine patients were prospectively studied at a peripheral clinic during the peak malaria season; symptoms and signs of the infection, parasite loads, haemoglobin values and leucocyte counts were recorded in all patients. Haemoglobin and leucocyte counts were also measured in 37 control subjects without malaria. The commonest symptoms were persistent headache (100%), rigors (98%) and myalgia (93%). None of the patients presented with coma, pulmonary oedema, hypoglycaemia or algid malaria. Splenomegaly was found in 49%, hepatomegaly in 20% and mental confusion in 5% of patients. Mean parasite load was 1.71% and 57% of patients had parasite loads of1%. Anaemia of10 g/dl was significantly more frequent (P0.0001) in the patient group than in the control group. Leucopenia (white cell count4.0 x 10(9)/l) was present in 12 of 50 patients in whom it was measured compared with 2 controls (P = 0.0175). The results show a wide range of morbidity, without severe complications as presenting manifestations. Symptomatic infection in the presence of low parasite loads suggests that there may be little or no immunity in this population.

The sensitivity to chloroquine of Plasmodium falciparum from the Kavango region of Namibia was determined by a 24-hour test in vitro. Twenty-six isolates were successfully tested, of which 11 were resistant to a low degree, schizogony being inhibited at 8 pmol/well. The results of the Dill-Glazko test for the presence of 4-aminoquinolines in urine indicate that chloroquine is not widely used in the area.

The effect of house spraying with DDT on blood-feeding and resting behavior of An. arabiensis in Natal Province, Republic of South Africa, was investigated. Indoor resting occurred in both control (unsprayed) and replastered (DDT on walls covered due to replastering) huts, but was minimal in fully DDT-sprayed huts. The percentage of bloodfed mosquitoes was greater than 50% in both control and replastered huts, but in the latter huts there was a reduction in the percentage of gravid and an increase in the percentage of unfed mosquitoes. Large numbers were collected in exit traps irrespective of the DDT status of the huts. The percentage of catch that was bloodfed was lowest in exit traps fitted on DDT-sprayed houses. The percentage survival of bloodfed mosquitoes caught in exit traps exceeded 72% for all 3 hut types. The survival of unfed mosquitoes was, however, markedly lower. Susceptibility tests showed no physiological tolerance to DDT by the wild An. arabiensis population. Bioassays using colonized An. arabiensis showed the DDT deposits on hut walls to effect 100% kill with 15 minutes of exposure.

The analytical capability of a d.c. capillary arc plasma, operating on argon, is described. Solutions containing Cd, Pb, Hg, I, As and Zn are introduced into the plasma from a tantalum-filament atomizer. Signals are observed from both the arc and the tail-flame. The problem of sample rejection by the hot plasma is illustrated and discussed.

Despite the profusion of literature associated with analytical atomic spectrometric techniques, very little has been reported concerning the development of detector systems. This is particularly surprising in view of the current trend in atomic spectrometry towards the use of non-flame atom reservoirs. These devices frequently produce weak transient signals and dc level detector systems designed for steady state measurements are in consequence often unsatisfactory. High speed recorders may be used with success providing the total response time of the various electronic components is comparable with or preferably less than that of the signal duration and only in such instances will precise measurement of the signal be achieved (1,2). The use of absolute integration techniques are obvious for this type of measurement, although their application has not been particularly forthcoming to date. Photon counting would seem to have many advantages for such purposes, although with the exception of the more...

A simple photon-counting system is proposed for conventional flame and non-flame atomic spectrometric purposes. The current pulses from the photomultiplier are amplified by a wide band-width amplifier and fed directly to a frequency meter. Discrimination is provided by the sensitivity control of the frequency meter. The system is evaluated with respect to frequency response, linear working range and as a digital integrating device.

A non-flame cell utilising a microwave-induced argon plasma at atmospheric pressure is described for emission spectroscopie purposes. The system operates at a microwave power of ca. 40 W (2450 MHz) and requires the use of only minute liquid samples. Optimal operating parameters are investigated and the method is tested on a range of elements. In addition, the use of a high-speed operational amplifier/integrator is described which is capable of following the weak and transient signals common to non-flame methods of atomisation.

This article shows that the availability of photomultipliers with gains of about 2 × 106 to 108 has obviated the need for an amplifier and that a system having no amplifier and a cooled photomultiplier does not require a pulse height discriminator for efficient operation.

Sixteen southern African isolates of Plasmodium falciparum were successfully established and maintained in gassed tissue culture flasks which were either held in a static position or shaken. Shaken cultures yielded 48-hour growth rates ranging from 3.9-fold to 9.5-fold and peak parasitaemias ranging from 9% to 27%. Growth rates in static flasks were lower, ranging from 1.8-fold to 4.2-fold every 48 hours with peak parasitaemias ranging from 4% to 12%. Four of the established isolates were treated so as to promote gametocytogenesis and the rate of gametocyte production was found to be high. The mean percentage gametocytes by day 20-25 was 4.2% of erythrocytes, which represented approximately 50% of total parasites.

In May 1987 and January 1988 the chloroquine sensitivity of Plasmodium falciparum in the Ubombo and Ingwavuma districts of KwaZulu was determined by a modified in vitro microtest in which the patients' plasma was replaced with non-immune human AB serum and the test plates were incubated in an atmosphere of 3% oxygen, 4% carbon dioxide and 93% nitrogen. A success rate of 74% was achieved using this technique. All of 23 successfully tested isolates from malaria patients reporting to clinics and a hospital in these areas were found to be resistant to chloroquine, schizogony being inhibited at 32 pmol per well in the majority of tests. Seventy-five per cent of the isolates obtained through active surveillance in the Ubombo district were found to be resistant in varying degrees. Malarial parasites collected from clinics and a hospital in the endemic area did not change markedly in their in vitro response to chloroquine during the 8-month period May 1987-January 1988.

An analysis is given of the statistics of photon-counting as a means of making measurements in atomic-absorption spectrometry. It is concluded that the simple application of Poisson counting statistics may give an over-optimistic estimate of the error, since other sources of error, such as flame flicker and variable nebulization rate, may be more significant.

RECENT advances in analytical atomic spectrometry have been concerned with the development of non-flame atom reservoirs, namely, the L'vov furnace1, the Massman furnace2, the filament atom reservoir3 and the platinum loop4. These devices give increased analytical sensitivity but the absorption or emission signals produced may be characterized by several peculiarities. First, the radiation signals derived are transient in nature; second, the signal profiles are usually asymmetric and may also be non-reproducible from sample to sample; and third, the signal duration may depend on sample concentration.