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| Thursday, 31 October 2002 |
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From the address of the President, Institute of Biology, Sri Lanka Dr. Preethi Randeniya at the 22nd Annual Sessions of the Institute of Biology held at the University of Colombo recently. In keeping with the theme of this year's annual sessions, Biology towards better health, I thought it most appropriate to examine the role of the Biologist in the new millennium, in the context of contributing to improve the quality of health of a nation, with particular emphasis on tropical diseases. Good health is an essential foundation for social and economic development. Parasites present an unacceptable threat to the well-being of approximately 500 million people in the tropics and the subtropics, most of whom are stricken with poverty. The consequences of parasitic diseases in terms of human morbidity, mortality, and economic loss are incalculable. These individuals suffer physically, including deformity, blindness, brain damage and premature death, psychologically and socially from the stress of severe disfigurement, and economically from an inability to work. Thus, tropical diseases are a serious impediment to individual and national development. These diseases impair intellectual and physical growth, make fertile land unusable, and burden economies with huge costs for treatment and control. Despite significant input of resources and effort over the past 50 years by governments, and national and international programmes to control tropical diseases, these still persist and constitute the majority of the burden of disease in the poorest countries. One in ten individuals on earth suffers from one or more of the major tropical diseases, of which three, namely malaria, lymphatic filariasis and cutaneous leishmaniasis, are significant in a Sri Lankan context. I shall therefore, restrict myself to these three parasitic diseases and attempt to briefly review the local and global situation, control measures and ongoing research on each of these, while emphasizing the need for new interventions for tropical diseases that are tomorrow's tools based on today's advances, that will hopefully facilitate long lasting solutions to these public health hindrances. Malaria Malaria remains to be by far the most important tropical parasitic disease in terms of suffering and loss of life. In humans malaria is caused by four species of protozoan parasites of the genus Plasmodium. P.falciparum causes the most dangerous form of the disease, leading to cerebral malaria, anemia and kidney failure. The other three are the relatively benign forms, P. vivax, P. malariae and P. ovale. Female mosquitoes of the genus Anopheles transmit the parasites. The malaria parasite during its life cycle in the human and mosquito hosts encompass a number of distinct stages. Malaria continues to be the major public health problem in the tropical world that is responsible for more than one million deaths, mainly children under five years in Africa, and almost 300 million clinical cases reported annually, worldwide. Malaria represents 2.3% of the overall global disease burden and rank third among major infectious disease threats, following respiratory infections and tuberculosis. Pregnant women and children under five years remain one of the most important risk groups. While closely linked to movement of refugees and populations seeking work and to environmental interventions, in 1990 this disease was responsible for the loss of 31.7 million Disability Adjusted Life Years. The estimated annual direct and indirect cost of malaria in Africa was US$ 800 million in 1985 that exceeded US$ 1800 million by 1995. Malaria has been a major public health problem and a socio-economic burden in Sri Lanka since ancient times. The worst malaria epidemic recorded to date, dates back to 1934/35 where 120,000 cases were reported with an astounding 80,000 deaths. An estimated population of 10.5 million lives in malaria endemic areas, in the dry and intermediate zones of the island. Over a long period, 9% of the national health budget and 30% of the public health budget is spent on malaria control. The principle vector in Sri Lanka is A.culicifacies. According to most recent statistics available for the year 2000, 212,400 clinical cases of malaria were detected in government medical institutions. P.vivax infections accounted for 72% of the caseload while the remainder was due to P.falciparum. A majority of malaria patients reported during this year, as was during the past few years, was from the North and Eastern Provinces. Seventy-six malaria related deaths were reported to the AMC of which, 70 were from the North Eastern Province. Control on Malaria in Sri Lanka Control of malaria takes a three-pronged approach i.e. attacking the parasite, attacking the vector and minimizing human-vector contact. The Malaria Eradication Programme launched in 1958 by the National Anti-Malaria Campaign (AMC) as per WHO recommendations, resulted in a near-eradication status in 1963 where only 17 malaria cases were reported from the country. However, due to a multitude of factors, resurgence of the disease occurred after a few years. Milestones in the control of malaria in Sri Lanka were the detection of DDT resistance in the vector mosquito, Anopheles culicifacies, in 1969 and that of chloroquine resistant P. falciparum parasites in 1984. The National Malaria Control Policy of the AMC has adopted the "Global Malaria Control Strategy" recommended by the World Health Organisation in 1993 that include the following four main principles: * Early detection & prompt treatment of malaria cases * Selective application of sustainable malaria control measures, including vector control * Development of mechanisms to forecast and prevent malaria outbreaks and epidemics * Regular reassessment of the malaria control programme in keeping with the changing socio-economic environment of the country Launched in October 1998, the WHO Roll Back Malaria partnership is committed to halving the global malaria burden by 2010. The core interventions specified therein are as follows: * Rapid diagnosis & treatment * Multiple prevention * Focused research to develop new medicines, vaccines and insecticides, and to support epidemiological and operational activities * Epidemic preparedness through improved surveillance and appropriate responses Sri Lanka has been one of the first countries in South East Asia to adopt the current priority programme of the Roll Back Malaria Initiative. Malaria Vaccines The emergence and spread of multi-drug resistance of the parasite and resistance of the vector mosquito to insecticides are major hindrances in controlling the disease. Among alternative control measures, vaccine development has been the central focus of malaria research for several decades and may be one of the most cost-effective interventions to reduce the burden of the disease. Vaccines under development are mainly based on raising immunity against different stages of the parasite's life cycle and comprise of 4 main types: 1. Pre-erythrocytic vaccines- are designed to prevent the parasite's infective sporozoite stage from entering or developing within liver cells of an individual bitten by an infective mosquito. 2. Asexual blood stage vaccines- target these stages of the malaria parasite to prevent it from entering or developing in red blood cells. 3 Anti-disease vaccines- some directed to the asexual blood stage antigens with the objective of reducing severe morbidity and mortality from malaria. 4. Transmission blocking vaccines- aim at abolishing the development of the malaria parasite in its mosquito host. These vaccine candidates may be based on recombinant proteins, synthetic peptides and DNA plasmids. A variety of malaria vaccine candidates are under development where some have reached Phase III clinical trials evaluating the efficacy of these candidates. Significant progress has been made over the last few years with respect of the development and clinical evaluation of promising vaccine candidates for malaria, specifically vaccines for P. falciparum malaria. There is little commercial interest in vaccines against vivax malaria and thus the development of these is proceeding slowly. However, it is heartening to note that at the Malaria Research Unit of the University of Colombo, attempts initiated in the discovery and development of vaccine candidates for asexual erythrocytic stage, anti-disease and transmission blocking vaccines against vivax malaria, are continuing. Attempts to develop a malaria vaccine were initiated early in the twentieth century. In spite of advances in bio-medical technology, with substantial progress made in identification of vaccine candidate antigens and of protective mechanisms, and in development of in vitro assays predictive of protection and in vaccine testing, much remains to be done. Major obstacle among others in malaria vaccine development lies in immune evasion mechanisms developed by the parasite. To date there is no effective vaccine available for widespread use. Pathogenesis and Applied Genomics Research is helping to clarify some of the pathologic mechanisms underlying the etiology and progression of different parasitic diseases, including the genetic background, and is contributing to the identification of potential drug and vaccine targets. The pathogenic effects of parasitic infections are unique to each parasite. In malaria, the pathology associated with P. falciparum malaria is mainly due to adherence of infected red blood cells in the brain resulting in metabolic disturbances and organ dysfunction. In order to attain the goal of "good health for all", it is imperative to facilitate greater involvement of in-country researchers, thereby increasing self-reliance in research in developing countries that are endemic to parasitic diseases. Furthermore, it should be a major responsibility of the State to support their own scientists endeavouring to serve the community in various capacities. In Sri Lanka, only a mere 0.18% of the GDP is spent on research and development. In addition, Scientists across the globe should unite in a serious commitment to fight parasitic diseases, which are diseases of poverty, with science. As biologists of the developing world, we should carry a "conscience" of science rather than enjoy intellectual exercises in research. If the fight against tropical diseases were to be won, it would need the wholehearted support of the entire international community. |
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