Malaria is a mosquito-borne infectious disease of humans and other animals caused by parasitic protozoans (a group of single-celled microorganism) belonging to the genus Plasmodium.[1] Malaria causes symptoms that typically include fever, fatigue, vomiting, and headaches. In severe cases it can cause yellow skin, seizures, coma or death.[2] The disease is transmitted by the biting of mosquitos, and the symptoms usually begin ten to fifteen days after being bitten. If not appropriately treated, people may have recurrences of the disease months later. In those who have recently survived an infection, re-infection typically causes milder symptoms. This partial resistance disappears over months to years if the person has no continuing exposure to malaria.
The disease is transmitted most commonly by an infected female Anopheles mosquito. The mosquito bite introduces the parasites from the mosquito’s saliva into a person’s blood. The parasites travel to the liver where they mature and reproduce. Five species of Plasmodium can infect and be spread by humans. Most deaths are caused by P. falciparum because P. vivax, P. ovale, and P. malariae generally cause a milder form of malaria. The species P. knowlesi rarely causes disease in humans. Malaria is typically diagnosed by the microscopic examination of blood using blood films, or with antigen-based rapid diagnostic tests
Malaria is endemic throughout most of the tropics. Of the approximately 3.4 billion people worldwide who are exposed annually, 1.2 billion are at high risk; the World Health Organization (WHO) states that there were 198 million cases of symptomatic malaria in 2013.
Between 2000 and 2010, the number of annual malaria cases reported by the WHO in 34 malaria-eliminating countries decreased by 85 percent from 1.5 million to 232,000 cases. Most of these are attributable to P. falciparum, but P. vivax and P. knowlesi can also cause severe disease. Malaria deaths peaked at 1.82 million in 2004 and fell to 1.24 million in 2010 (714,000 children <5 years and 524,000 individuals ≥5 years); over 80 percent of the deaths occur in sub-Saharan Africa. The WHO’s estimates of deaths from malaria (627,000 in 2012; uncertainty range 473,000 to 789,000) are approximately half the more reliable estimates above.
Important components for reducing the burden of malaria morbidity and mortality include more sensitive diagnostic tools, effective use of antimalarial drugs, and improved personal and community protection and mosquito control. The approach to elimination or control of malaria includes these basics, along with improvements in tracking of human illness and parasite surveillance, and effective resource delivery.
Issues related to epidemiology of malaria, including definitions and strategies for control, will be reviewed. Other related topics are discussed in detail separately.
Overview — Malaria is transmitted via the bite of a female Anopheles spp mosquito, which occurs mainly between dusk and dawn. Other comparatively rare mechanisms for transmission include congenitally acquired disease, blood transfusion, sharing of contaminated needles, and organ transplantation
The epidemiology of malaria in adults who live in malaria endemic areas is a neglected area of research. Malaria control strategies have focussed on children under the age of 5 years and pregnant women, as the majority of malaria-related sickness and death is seen in these two groups. However, early studies in West Africa showed that clinical attacks of malaria also occur in adults living in areas of high endemicity and a recent report points out the considerable contribution of malaria as a cause of death in adults.
The risk of malaria attacks in residents of malaria endemic areas falls as they become older, suggesting that protection is a function of age. This protective immunity is sequentially being reflected first by a reduction of life-threatening disease, then by a fall in the incidence of mild malaria and finally by a reduction in parasite prevalence. The means by which acquired immunity develops is still a matter of contention. It is likely that cumulative exposure to the enormous repertoire of antigenic variants of blood stage malaria parasites plays an important part. However, there is evidence which suggests that protection can be established after a relatively brief period of exposure and lasts for many years. Indeed, passive transfer of naturally acquired immunity and malariotherapy of syphilitic patients have suggested that there is a strong component of non-variant specific immunity involved in the protection against malaria which may be age-dependent.
The immune mechanisms that deal with a malarial infection probably change with age, as suggested by the age-dependency of malariometric indices, the pyrogenic threshold of parasitaemia, the speed with which infections are controlled, the incidence of clinical episodes and the parasitological complexity of individual infections. It is generally accepted that protective immunity effectively prevents the severe clinical manifestations of Plasmodium falciparum infections and substantially reduces parasite loads, but does not prevent infection. The consequence of this process is that the presence of blood-stage parasites in a semi-immune host is not synonymous with disease. This, together with the non-specificity of the malaria signs and symptoms in adults, make the individual diagnosis of clinical malaria in adults difficult in highly endemic areas.
Studies of malaria in semi-immune adults of Africa are scarce. More attention to the natural history of malaria affecting adults is needed to understand the dynamics of malaria infection and its interaction with the immune system. The present study was undertaken to investigate the clinical, parasitological and haematological status of adults living in a region in Mozambique where malaria is endemic, and to characterize parasites in these individuals who progressively acquire protective immunity.
Malaria is a life threatening parasitic disease transmitted by female anopheles mosquitoes. There are four types of human parasites; Plasmodium vivax, P. malariae, P ovale and P. falciparum. P. falciparum and P. vivax are the most common and P. falciparum, the most deadly type of infection, is most common in sub-Saharan Africa. A large number of environmental factors affect the distribution, seasonality and transmission intensity of malaria. Rainfall provides breeding sites for mosquitoes and increases the humidity, which enhances their survival. While malaria is largely endemic in Africa, varying proportion of countries in the continent are at risk of endemic malaria. Today, approximately 40% of the world population, mostly those living in the world's poorest countries, is at risk of malaria. This is mostly in the tropical and sub-tropical regions of the world. There are at least 300 million acute cases of malaria each year globally resulting in more than a million deaths, around 90% of these occur in Africa, mostly young children. In areas of stable malaria transmission, very young children and pregnant women are the population at highest risk for malaria morbidity and mortality. The populations most at risk of epidemics are those living in highlands, arid and desert-fringe zones and those living in areas where successful control measures have not been consolidated or maintained.
Malaria has been recognised as a severe and life-threatening illness for thousands of years. It still is one of the most common diseases affecting humans worldwide. The major impact of the disease is almost entirely on the developing countries, with the heaviest burden in Africa. Almost half of the total world population is exposed to the risk of contracting malaria.
Along with direct health cost there is a severe economic burden of the disease in terms of lost days of work. In fact malaria is thought to take off 1.3% from the economic growth of some African countries. In some of the most severely affected countries, it accounts for 40% of public health expenditure, 30-50% of inpatient admissions, and 50% of outpatient visits. It affects developing countries in more ways than one including determent of tourism.
There were an estimated 219 million cases of malaria (154–289 million) and 660 000 deaths (range 610 000–971 000) in 2010. Of total numbers 80% of estimated malaria deaths occur in just 14 countries and approximately 80% of estimated cases occur in 17 countries.
The Democratic Republic of the Congo and Nigeria account for over 40% of the estimated total of malaria deaths globally. The Democratic Republic of the Congo, India and Nigeria account for 40% of estimated malaria cases.
Estimated malaria mortality rates are highest in countries with a lower GNI per capita. Countries with higher proportions of their population living in poverty (less than US$ 1.25 per person per day) have higher mortality rates from malaria.
Of the deaths a large proportion was young children in sub-Saharan Africa. This is the most vulnerable group affected with the condition. In areas with high transmission, the most vulnerable groups are young children. These children are vulnerable because they have not developed immunity to malaria yet. Pregnant women are also at risk because their immunity has been decreased by pregnancy.
Malaria affects mainly poor tropical and subtropical areas of the world. Where the disease is endemic it is the leading cause of illness and death.
Africa has several factors that make it high risk for malaria. Some of these include very efficient mosquito (Anopheles gambiae) responsible for transmission, predominant parasite species is Plasmodium falciparum that leads to more severe malaria, warm and humid climate that allows transmission to occur year round as well as lack of resources and poor socio-economic conditions that prevents malaria control efforts. Other areas that are at risk include some countries in South America and South Asia.

To summarize, malaria is the leading cause of death and disease in many developing countries. According to the World Health Organization’s World Malaria Report 2011 and the Global Malaria Action Plan, 3.3 billion people worldwide live in areas at risk of malaria transmission in 106 countries and territories.
In 2012 malaria led to 216 million clinical episodes, and 655,000 deaths. An estimated 91% of deaths in 2010 were in the African Region, followed by 6% in the South-East Asian Region and 3% in the Eastern Mediterranean Region (3%). 86% of all deaths worldwide are children.

• WHO. World Malaria Report 2014. Geneva, Switzerland http://www.who.int/malaria/publications/world_malaria_report_2014/report/en/ (Accessed on December 18, 2014).
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