Environmental Science

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The epidemiology of malaria in Zambia.
(2003) Chimumbwa, John Mulenga.; Sharp, Brian Leslie.; Appleton, Christopher Charles.
Nearly half of the world's population lives in tropical and temperate climates where they may be at risk from one or more vector borne diseases. Approximately 2.1 billion people, living in more than 100 countries are at risk from malaria. While the malaria situation has improved in some places, the overall prevalence in Africa, Asia and the Americas continues to deteriorate. This has led nations, institutions, organisations and agencies including the World Health Organisation to call for development of new and innovative approaches to its surveillance and control. In nature, maintenance of malaria transmission involves a complex interaction between the mosquito vector, the human host, the disease organism, and both the internal and external environments. An understanding of this complex relationship is the key to the prevention, control and eventual eradication of malaria. Malaria prevention and control programmes do not only have to be based on sound knowledge of how these factors interrelate, but also on an application of the political will of the concerned authorities. This study attempts to identify some determinants of malaria and to characterise it in epidemiological zones in Zambia. The study aims at contributing to the body of knowledge that would support implementation of an evidence-based national malaria programme. This study has come at an opportune time when there is renewed focus on malaria prevention and control globally. It is hoped that these aspects of the malaria programme in Zambia will not have to be rewritten in the foreseeable future, instead will be improved upon in order to progress to the delivery of quality assured malaria services as close to the family as possible based on the principles of community-health partnerships. The study is presented in a series of chapters; each developed as a follow up to the previous one and forms a bridge to the next. In this way, it enables the reader to build a relatively complete picture of the malaria situation in the country. However, some repetitions could not be avoided with regard to descriptions of study sites. In the chapters dealing with health systems and quantification of malaria risk, the country (Zambia) is taken as the study site. The remaining sections are based on specific sites, selected on the basis of their representing different aspects of the malaria situation in the country. Mapping of households and other referral points provided the basis upon which a Malaria Information System would in future be built. One of the two study sites was special because most of the previously conducted malaria research in Zambia has been conducted at this site. While the other was not only new in terms of malaria research, it also represented locations in the high rainfall zone in Zambia. The introductory chapter sets out the general principles of Geographical Information System (GIS), malariology, entomology, and health systems. The chapter reviews the current global burden of malaria including its implications for economic development of endemic subSaharan African countries, and discusses progress made in the light of drug and insecticide resistance and the changing global weather patterns. This section examines the position of the African continent in relation to the global malaria eradication era and the possible reasons why it was excluded from the global malaria eradication campaign of 1956-1969. It goes on to analyse new obstacles being faced in rejuvenating global interest in malaria programmes, starting with Primary Health Care through to the principles of Roll Back Malaria (RBM). It also emphasizes special Africa-specific initiatives related to malaria, such as the MARA/ARMA collaboration which (through the use of GIS) is providing a basis for evidence-based decision making. The fist chapter deals with the historical aspects of malaria control in Zambia. It traces how malaria was successfully controlled over a period of 46 years. It starts with a rural set up where copper mineral deposits were discovered. From there it traces the history of malaria control spanning almost eight decades to the present day. It outlines the major milestones in both the malaria programme and in the political history of the country; from a British protectorate , through Federation to the present day nation, Zambia. The chapter demonstrates how malaria can be controlled in an intense transmission situation, using a combination of simple and relatively cost-effective interventions. It also demonstrates that political will is an essential element to disease control. The second chapter examines the role of health systems in the delivery of quality, efficient and cost-effective services to the population. It examines the adequacy of health services in the light of time-limited Roll Back Malaria goals, according to the Abuja Declaration of 2000. This chapter analyses the capacity of the local health system to deliver on its health vision of taking quality assured health services (Malaria services) as close to the family as possible. Together, these goals are examined in terms of population accessing the facilities within 30 minutes' walking distance. Chapter three focuses on identifying factors that facilitate or hinder households acquiring and using Insecticide Treated Nets (ITNs) in the same locality. Specifically, distance of households to some reference points is examined. Also the effects of social, economic and educational status of heads of households are analysed. Together all parameters are analysed statistically to isolate the important reasons why some homes acquire ITNs while others do not. The study concludes with an analysis of the importance of ITN s in averting malaria among users. Some anecdotal evidence resented on the value of ITN s in reducing malaria incidence in the general population is presented. GIS is employed in the fourth chapter to produce a malaria endemicity risk map for the country. It employs population Plasmodjum faldparum infection rates. It proposes stratification and compares it with existing expert opinions and the climate-based Fuzzy Logic predictive model. The resultant malaria risk map is verified against existing maps and expert opinions. The chapter then discusses application for local decision making on policy and action. Chapter number five is dedicated to identifying and studying the bionomics of malaria vectors at two sites. It reviews existing literature on this subject, from 1929 to date. It identifies possible malaria vectors, their behaviour and ecology at two sites representing two extreme situations of malaria endemicity in the country. The combination of Anopheles vector densities and their reliance on temperature and rainfall are analysed and the implications discussed. The chapter also looks at possible ways forward for the country in the light of the paucity of information in this respect. P. faldparum infection rates are estimated together with their entomological inoculation rates and possible implications for malaria transmission potential. The final section (chapter six), highlights the major lessons and their implications for global goals and local health policies. It also outlines the way forward chapter by chapter.
Geohelminth transmission among slum-dwelling children in Durban, South Africa.
(2001) Mosala, Thabang Innocentia.; Appleton, Christopher Charles.; Olsen, Annette.
Geohelminthiasis is a serious problem in city slums and despite being easily treatable in the short term, its elimination enjoys a low priority by parents, teachers and public health authorities. This is partly due to the greater emphasis given to the AIDS and TB programmes. This study of the prevalence, intensity, and reinfection rates of single and multiple geohelminth (Ascaris lumbricoides, Trichuris trichiura and Necator americanus) infections in young children living in slums (informal settlements) in the Durban Unicity is a first for an African city and one of few similar studies anywhere in the world. The geohelminth status was assessed by means of a baseline survey of ten different slums, followed by two further surveys, one after 4Y:z - 6 months and another after 12 months. Infections were measured by microscopic examination of faeces before and after chemotherapy, and risk factors within and between slums were identified by means of a quantifiable questionnaire. The study showed that: 1. The slums have a high endemicity and transmission rate of geohelminth infections. 2. The sub-tropical climate and environment ensured a high survival rate of infective stages. 3. A. lumbricoides had a high prevalence and intensity, followed by T. trichiura with a moderately high prevalence and light intensity. A small proportion of children had intensities of these helminths an order of magnitude higher than previously recorded from rural areas of South Africa. N americanus had a very low prevalence and a very light intensity. 4. Egg output from follow-up 1 to follow-up 2 increased 4.6 fold for A. lumbricoides and 9.4 fold for T. trichiura. 5. Albendazole proved to be a very effective drug against A. lumbricoides and N americanus but not as effective against T. trichiura. 6. The infection and reinfection rates of A. lumbricoides and T. trichiura proved to be influenced by different risk factors. 7. The most important risk factors included topographical position of the slum, quality of the dwelling, number of inhabitants, geophagy and source of fruit and vegetables. II Whereas the ideal solution to the geohelminth problem in the slums would be to upgrade the slum and its inhabitants, this is not an immediately viable option. The challenge of geohelminth control in these slums must be to determine the degree of environmental contamination by human faeces containing infective eggs, to ascertain the survival rate of the eggs and larvae and to implement a control programme together with suitable education of the inhabitants. The Parasite Control Programme should take into consideration that many slum-dwelling children do not go to school and need to be treated at home. A further factor that will have to be taken into account is that lack of influx control to urban areas will mean the continual reinfection of slum-dwellers by the movement from the rural areas.
Modelling schistosomiasis in South Africa.
(2003) Moodley, Inbarani.; Appleton, Christopher Charles.
Temperature and rainfall vary spatially within South Africa and they in turn affect the parasites and intermediate host snails involved in schistosomiasis transmission. The primary goal of this study was to investigate the relationship between these two abiotic variables and schistosomiasis in South Africa using a Geographic Information System (GlS) as a spatial analytical tool. The secondary goal was to estimate the population exposure to schistosomiasis. Prevalence data for Schistosoma haematobium and S. mansoni obtained from a national hardcopy atlas and two long-term, retrospective, high resolution climate datasets were used to produce two models (temperature-suitability and regression analysis) based on different GIS methodologies. The temperature-suitability model defined areas that are suitable and unsuitable for disease transmission by relating documented temperature regimes to the schistosomes' larval biology. The map outputs show that temperature minima corresponded better with the disease data than temperature maxima. Based on different climate and population data permutations, between approximately 3 903 734 and 4 379 079 school-aged children live in these temperature-suitable zones. The regression model tested the hypothesis that temperatures, especially during spring and summer favoured schistosomiasis transmission more than those of autumn and winter. Positive associations were expected with the rainfall variables. A logistic equation was used to predict, as accurately as possible within the model's limitations, the probability of schistosomiasis occurring in a given area. Increasing annual rainfall, as well as spring and autumn temperature maxima and minima predicted an increase in S. haematobium prevalence rates. Schistosoma haematobium prevalence rates of 11-25% and 26-50% were predicted in the north-eastern and eastern coastal regions. A prevalence rate of 71 to 100% was predicted from Limpopo to KwaZulu-Natal. Increasing the average monthly rainfall, spring temperature maxima and autumn temperature minima, increased the likelihood of S. mansoni transmission. Schistosoma mansoni prevalence rates of 26-50% and 71 to 100% were predicted in Limpopo, Mpumalanga, KwaZulu- Natal and Eastern Cape. This is the first time GIS has been used to correlate climate variables and schistosomiasis occurrence in South Africa. The regression model requires further refinement and it is not as applicable as the temperature-suitability model for practical purposes.
Some aspects of the epidemiology of intestinal protozoan infections in KwaZulu-Natal, South Africa.
(2001) Khabisi, Mamohale Eugenia.; Appleton, Christopher Charles.
This study was carried out to investigate different aspects of the epidemiology of the common intestinal protozoan infections in children in KwaZulu-Natal. The main aspects studied were to: i . monitor changes in the prevalence and intensity of the common intestinal protozoons in children after receiving antihelmintic drugs, ii. determine whether environmental and/or socio-economic factors are important in the prevalence of the common intestinal protozoons, iii. determine the occurrence of Cryptosporidium parvum in stool samples of paediatric patients with gastroenteritis and in healthy school children. Intestinal protowan species often co-occur with intestinal nematodes in infected children and it is important to determine the effect that anti-nematode treatment has on concomitant protozoan infections. The study included the analysis of stool samples by the Formol-Ether Concentration Technique, exam ination of the obtained sediments for intestinal helminths and protozoan species, and treatment of nematode-infected individuals. Four surveys were carried out to determine the prevalence and intensity of intestinal protozoons in school children before and after anthelmintic chemotherapy, and the X(2) test was used to determine significant changes. Prevalences and intensities of helminths were determined for significant changes after treatment using the Student's t-test. Additional pre- and post-treatment prevalence data were obtained from four schools in Health Region A of KwaZulu-Natal. The prevalence of Ascaris lumbricoides decreased significantly from 75.2% to 9.7% after the first treatment, that of Trichuris trichiura decreased from 77.7% to 62. 1%, and hookworm infections (presumably Necator americanus) dropped fromI2.7% to 1.0% and remained very low for the rest of the study. Very few individuals were infected with protozoan species and for statistical analysis, these were combined. The prevalence of protozoan infections increased from 33.0% to 50.3% after the first treatment and from 35% to 42% after the second treatment. The prevalence of A. lumbricoides decreased significantly again after the second treatment while there was no significant decrease in the prevalence of T. trichiura. The intensities (number of eggs/gram of feaces) of the three nematodes also decreased significantly after the two treatments. It is recommended that children who have been treated for nematode infections should also be examined for protozoan infections, and these should also be treated accordingly. A retrospective analysis of protozoon prevalence data from different surveys in KwaZulu-Natal was done in order to detennine the importance of environmental and/or socio-economic factors in the distribution of intestinal protozoons. These data were plotted on the map of KwaZulu-Natal using Geographic Information System (GIS). Univariate analysis was carried out to determine significant correlations between the prevalences of protozoan species and selected variables. The significant correlations obtained were moderate and no strong correlations were obtained. Univariate stepwise regression analysis was performed to determine the factors that combine best in facilitating the transmission of protozoan species and significant associations were obtained between the prevalence of protozoon species and a combination of environmental and socio-economic factors. In most cases, the association between prevalence and mid-summer temperature and rainfall were the most significant. This is an indication of increased summer transmission. Altitude was significantly correlated only with the prevalence of Endolimax nana. The fact that moderate correlations were obtained between prevalence of intestinal protozoons and climatic and socio-economic factors indicates that these factors are important in the distribution of the common intestinal protozoons. However, lack of strong correlations suggests that in addition to climatic and socio-economic factors, there are other factors that have an effect on the distribution of intestinal protozoan species. In the multivariate analysis where the variables were simultaneously considered, the presence of electricity was the only factor that was significantly associated with the variation seen in the prevalence of intestinal protozoons in the different study locations. Cryplosporidium parvum is a parasitic protozoon that is associated with severe fatal diarrhoea in children and immunocompromised individuals. Oocysts of this parasite were found in 18.2% of stool samples collected from children (aged 6 to 48 months) who were admitted in the paediatric wards at King Edward VIII Hospital, Durban. The stool samples were firstly concentrated using the Formal-ether method and the obtained sediment was mixed with the Sheather's Sucrose solution and examined microscopically. No oocysts were found in stool samples collected from older primary school children. Although the diarrhoea in these children might have also been due to other causes, the results obtained further show the importance of C. parvum as a cause of diarrhoea in children below the age of five years. Knowledge of the epidemiology of C. parvum is crucial in the control of this parasite as there is currently no effective treatment. More intensive surveys are needed in detennining the epidemiology of this pathogen in the South African population.

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