الفهرس 
Epidemiology of MalariaOnly 14 pages are availabe for public view
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Abstract
Malaria is a vector-borne infectious disease caused by Plasmodium(P) parasites. Four species of plasmodium are known which are P. falciparum ,P.vivax ,P.ovale and P. malariae. It is widespread in tropical and subtropical regions, including parts of the Americas, Asia, and Africa. Each year, there are approximately 350–500 million cases of malaria killing between one and three million people, the majority of whom are young children in Sub-Saharan Africa. Ninety percent of malaria-related deaths occur in Sub-Saharan Africa. Malaria is commonly associated with poverty, but is also a cause of poverty and a major hindrance to economic development.
Clearly, this disease must be stopped. While drugs, insecticide-treated bed nets, and other interventions are currently being used to help reduce malaria’s impact, the parasite is complex and adaptable, and it has survived for millennia. We need many tools to defeat this disease—tools that save lives today and those with the potential to save lives in the future. A safe, effective, and affordable malaria vaccine would close the gap left by other interventions.
The aim of this wotk is to review the literature as regards malaria vaccines trials up to date .
Development of a malaria vaccine has been difficult. Greatly expanded investment in malaria vaccine research and development in recent years has resulted in the identification of a substantial number of vaccine candidates that are now in clinical trials or in the late stages of preclinical development. Now the malaria vaccine community is faced with a new challenge. The vaccine development plans developed several years ago, when the main target of malaria vaccine development was reduction in the burden of clinical malaria, fit with the new and ambitious aim of achieving malaria elimination. Here the current situation with respect to malaria control, the particular challenges elimination strategies present, and the progress being made in vaccine development are considered. An assessment is made of what vaccines are needed and how they could be used most effectively as part of a malaria elimination programme .
Elimination programmes are focused on populations, not individuals, and, optimally, a herd immunity that is sustained and prevents transmission is required. The current vaccine development programmes are largely concerned with disease control and must be sustained, but, from the results obtained so far in clinical trials of the RTS, S vaccine, has a greater impact on severe disease than on infection. It is difficult to imagine partially effective asexual blood stage vaccines being very useful for parasite elimination. Given that all age groups can potentially provide a source of infection to mosquitoes, a high proportion of the population will need to be given a vaccine. However, there is much evidence to show that malaria is a highly focal disease and, initially at least, it might be beneficial to vaccinate those at greatest risk of being bitten by vector mosquitoes. Whatever vaccine is employed, pre-erythrocytic or transmission-blocking, its efficacy would need to be very high to achieve elimination .
A transmission-blocking vaccine has no direct effect on clinical malaria, but would break the life-cycle between human and mosquito . It might be used as a stand-alone vaccine, but, more appropriately, as part of an integrated programme involving drug-treatment and vector control.
The concept of a multi-component, multi-stage vaccine with an effect from one component mainly on disease and from another infection is intuitively appealing though the type of vaccine design required to kill parasites or render gametocytes non-infective to mosquitoes might be quite different from vaccines whose beneficial effect is mainly against disease severity. What is needed is an expanded malaria vaccine programme targeting the particular requirements of malaria elimination.
The challenges set to vaccine developers by those who drew up the malaria vaccine road map are first, by 2015, to produce a licensed vaccine that has a protective efficacy of more than 50% against severe disease and death from malaria which lasts longer than one year. Secondly, by 2025, to develop a vaccine with a protective efficacy greater than 80% against clinical disease and death that lasts longer than four years.
These targets focus on the prevention of clinical disease, especially its severe and life-threatening form, valid objectives for vaccines that are to be introduced into areas of medium or high transmission. A vaccine that conformed to the 2015 objective, providing protection to half of those vaccinated, would be valuable as part of an integrated control programme alongside vector control and chemo-preventative measures. That level of efficacy would not justify its use alone as an alternative to other means of malaria control.