Impact of DDT re-introduction on malaria transmission in KwaZulu-Natal.

OBJECTIVES: To determine whether the re-introduction of DDT in KwaZulu-Natal had any effects on malaria transmission in the province. DESIGN, SETTING AND SUBJECTS: 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. OUTCOME MEASURES: The notified malaria cases and the distribution of A. funestus were measured to determine the effects of DDT re-introduction on malaria transmission. RESULTS AND CONCLUSION: 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.

Exploring 30 years of malaria case data in KwaZulu-Natal, South Africa: part I. The impact of climatic factors.

Large parts of Africa are prone to malaria epidemics. Advance epidemic warning would give health services an opportunity to prepare. Because malaria transmission is largely limited by climate, climate-based epidemic warning systems are a real possibility. To develop and test such a system, good long-term malaria and climate data are needed. In KwaZulu-Natal (KZN), South Africa, 30 years of confirmed malaria case data provide a unique opportunity to examine short- and long-term trends. We analysed seasonal case totals and seasonal changes in cases (both log-transformed) against a range of climatic indicators obtained from three weather stations in the highest malaria incidence districts, using linear regression analysis. Seasonal changes in case numbers (delta log cases, dlc) were significantly associated with several climate variables. The two most significant ones were mean maximum daily temperatures from January to October of the preceding season (n=30, r2=0.364, P=0.0004) and total rainfall during the current summer months of November-March (n=30, r2=0.282, P=0.003). These two variables, when entered into the same regression model, together explained 49.7% of the total variation in dlc. We found no evidence of association between case totals and climate. In KZN, where malaria control operations are intense, climate appears to drive the interannual variation of malaria incidence, but not its overall level. The accompanying paper provides evidence that overall levels are associated with non-climatic factors such as drug resistance and possibly HIV prevalence.

Exploring 30 years of malaria case data in KwaZulu-Natal, South Africa: part II. The impact of non-climatic factors.

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.

Use of generalized linear mixed models in the spatial analysis of small-area malaria incidence rates in Kwazulu Natal, South Africa.

Spatial statistical analysis of 1994-1995 small-area malaria incidence rates in the population of the northernmost districts of KwaZulu Natal, South Africa, was undertaken to identify factors that might explain very strong heterogeneity in the rates. In this paper, the authors describe a method of adjusting the regression analysis results for strong spatial correlation in the rates by using generalized linear mixed models and variograms. The results of the spatially adjusted, multiple regression analysis showed that malaria incidence was significantly positively associated with higher winter rainfall and a higher average maximum temperature and was significantly negatively associated with increasing distance from water bodies. The statistical model was used to produce a map of predicted malaria incidence in the area, taking into account local variation from the model prediction if this variation was supported by the data. The predictor variables showed that even small differences in climate can have very marked effects on the intensity of malaria transmission, even in areas subject to malaria control for many years. The results of this study have important implications for malaria control programs in the area.

Comparison of the cost and cost-effectiveness of insecticide-treated bednets and residual house-spraying in KwaZulu-Natal, South Africa.

Residual house-spraying (RHS) has been the mainstay of South African malaria prevention for more than 50 years, but it has been argued that insecticide-treated bednets (ITBN) could be a more effective and appropriate method of control. To provide a rational basis for choosing between the interventions, a trial was conducted during 1998 and 1999 in northern KwaZulu-Natal to collect comparable data on the effectiveness, acceptability and cost of the two interventions. The current practice of house-spraying once a year was compared with ITBN, distributed free to households and retreated annually at several specific centres. The base case results show ITBN to be significantly more effective in preventing malaria cases than RHS (overall adjusted rate ratio of 0.69), and also more costly, with an incremental economic cost per person of ITBN compared with RHS of R8.68 (US$1.42) per year, giving a gross incremental cost per case averted of R111 ($18) (1999 prices). Estimating the number of deaths averted, based on the average case fatality rate, gave a gross incremental cost per death averted of R11 718 ($1915). The additional cases averted were estimated to lead to drug cost savings of around R1 ($0.16) per capita per year, giving a net cost per case averted of R98 ($16), and net cost per death averted of R10 377 ($1696). Although the finding that the economic costs of ITBN were higher than those for RHS was relatively robust to parameter variations, the extent of the cost margin was sensitive to changes in the price and useful life of the net, and the price of the insecticide. Moreover, a switch to ITBN could lead to net financial savings if the price per net fell below $3.57 (R21.85), or if a change in policy allowed a significant reduction in the number of permanent full-time malaria control staff. In view of the greater effectiveness of ITBN, policy makers may view ITBN as a cost-effective use of resources, even if the economic costs are higher. If ITBN are implemented, close monitoring will be required of use, retreatment and useful life of nets, and resistance to insecticides, to assess any change over time in relative cost-effectiveness, and any threat to the role of the programme as a barrier to the spread of malaria transmission to other areas.

Malaria control--two years' use of insecticide-treated bednets compared with insecticide house spraying in KwaZulu-Natal.

OBJECTIVES: 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. DESIGN, SETTING AND SUBJECTS: 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. RESULTS AND CONCLUSIONS: 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.

Chloroquine-resistant isolates of Plasmodium falciparum with alternative CG2 omega repeat length polymorphisms.

A particular polymorphism in the cg2 gene has previously been linked to chloroquine resistance in reference isolates of Plasmodium falciparum. To assess the association of this polymorphism with chloroquine resistance in field specimens of P. falciparum, we analyzed the omega repeat region of the cg2 gene in 47 isolates of P. falciparum collected in the Ingwavuma District of northern KwaZulu-Natal, South Africa. Polymerase chain reaction (PCR) primers, which were designed to amplify the region of DNA surrounding the omega repeat, were used to obtain omega repeat PCR products from the field isolates. The PCR product for each isolate varied in length, depending on the number of cg2 omega repeats for that isolate. We found that several in vivo and in vitro chloroquine-resistant isolates of P. falciparum did not have the expected 16 omega repeats. These results suggest that the link between the cg2 polymorphism and chloroquine resistance identified previously may not apply in all malarious areas.

Using a geographical information system to plan a malaria control programme in South Africa.

INTRODUCTION: Sustainable control of malaria in sub-Saharan Africa is jeopardized by dwindling public health resources resulting from competing health priorities that include an overwhelming acquired immunodeficiency syndrome (AIDS) epidemic. In Mpumalanga province, South Africa, rational planning has historically been hampered by a case surveillance system for malaria that only provided estimates of risk at the magisterial district level (a subdivision of a province). METHODS: To better map control programme activities to their geographical location, the malaria notification system was overhauled and a geographical information system implemented. The introduction of a simplified notification form used only for malaria and a carefully monitored notification system provided the good quality data necessary to support an effective geographical information system. RESULTS: The geographical information system displays data on malaria cases at a village or town level and has proved valuable in stratifying malaria risk within those magisterial districts at highest risk, Barberton and Nkomazi. The conspicuous west-to-east gradient, in which the risk rises sharply towards the Mozambican border (relative risk = 4.12, 95% confidence interval = 3.88-4.46 when the malaria risk within 5 km of the border was compared with the remaining areas in these two districts), allowed development of a targeted approach to control. DISCUSSION: The geographical information system for malaria was enormously valuable in enabling malaria risk at town and village level to be shown. Matching malaria control measures to specific strata of endemic malaria has provided the opportunity for more efficient malaria control in Mpumalanga province.

Comparative evaluation of four techniques for the diagnosis of Plasmodium falciparum infections.

Four diagnostic techniques for Plasmodium falciparum infection were evaluated against serial parasite dilutions and on identical field samples. These were (i) Giemsa-stained thick blood films (GTF), (ii) acridine orange-stained thick (AOTF) and thin (AOTnF) blood films, (iii) the quantitative buffy coat technique (QBC); and (iv) the ParaSight-F dipstick test (PS). PS had a consistently higher sensitivity and speed, was easiest to learn, and required no laboratory facility. The 100% sensitivity cut-off points against known parasite densities (per mm3) were: PS, 30; GTF, 84; QBC, 84; AOTnF, 84; AOTF, 149. In the field study, test sensitivities compared with examination of 800 microscope fields of a Giemsa-stained thin blood film were PS, 96.6%; AOTF, 93.1%; GTF, 91.4%; QBC, 89.7%; AOTnF, 82.8%. In the dilution study, one false positive result was recorded with QBC; in the field study there was one false positive each with PS, AOTnF and AOTF. When a newly trained microscopist examined samples of the parasite dilutions, the 100% sensitivity cut-off points were AOTF, 84; GTF, 140; QBC, 390. Total handling time was shortest with PS regardless of whether samples were processed individually or in batches of 10 or 100. The ParaSight-F test is recommended as the diagnostic tool for the future.

[Malaria in South Africa: past, present and perspectives]. / Le paludisme en Afrique du Sud: passé, présent et perspectives.

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.