LITERATURE REVIEW OF MALARIA IN THE WORLD TODAY

The name malaria is derived from two latin words mal; aria meaning “bad air”. This is due to the mistaken belief that it was caused by bad air following the observation that it occurred more frequently around damp places and marshy areas. Almost all races of human beings have at one time or another suffered from malaria (Bruce-chatt1983). Malaria is one of the most serious health problems facing the world today. Malaria is caused by infection with a microscopic parasite
and is transmitted to humans by the bite of certain sorts of mosquito called anophelines (WHO 1998). Of all the human parasitic infections, malaria caused by four (4) species of parasitic protozoa belonging to the genus plasmodium (  P); debilitates and kills more people than any other single infection disease.The four species of plasmodium are: 

Plasmodium falciparum, P. ovale, P. vivax and P. malaria, have their respective morphology, biological and clinical characteristics. The P. ovale, P. vivax and P. malaria are classified as relapsing malaria because they have a secondary or persisting stage of their life cycle (Perin et al 1984). 

        Life cycle of malaria parasite consists of sexual cycle that takes place in the mosquito and an asexual cycle that occurs in the vertebrate host. Life inside the mosquito is a race against time, because the time taken for the parasite to go through its growths and development is close to the average life span of the insect. 

This period is longer in cooler environment and shortens as the temperatures rises. It is for this reason that malaria is such a threat to health in the tropics and one of the many threats posed by global warming could extend the territory in which malaria is a health problem (WHO 1998). Every year, between 300 and 500 million people suffer clinical malaria, 1.5-2.7 millions die. Malaria is indigenous when natural to an area and imported when acquired outside specific area. Infections deliberately produced for the purpose of research or caused accidentally (by blood transfusion or other routes) are known as induced malaria (Wilcox, and Manson-Bahr 1983).

Malaria is still the most important parasitic disease in the tropics. It causes greater economic lose than any other disease in areas of high transmission such as the wet savanna areas of tropical African, Children under the age of 8 and women in their first pregnancy are most vulnerable to the disease. The effects of malaria are noticeable in rural areas where malaria frequently strikes during that period of the year when the need for agricultural work is greatest (WHO, 2000).

In many of these areas, the health infrastructure is not sufficiently developed to ensure that an evolving favorable epidemiological situation is maintained. Studies in rural areas of Africa where malaria is endemic revealed that over one third of primary school children had malaria during a school term, more than half of this group had two or more attacks typically missing a week or more of school with each attach(WHO, 1996). At a rural clinic in tropical Africa, it would not be unusual to find each of the following patients waiting for attention; A man complaining of feverishness for the past two days but he is still able to work, but requires for treatment to make him feel better; A child whose mother is worried because the boy looks dull and seems less energetic than usual; A young girl who is hot, deeply unconscious and having repeated convulsions of the whole body, each of these patients is suffering from malaria.

        For the first, its simply a nuisance; for the second, profound anemia has developed, which could be fatal if untreated, for the third the function of the brain has been affected and the child is in danger of losing her life. The illnesses in the second and third of these individuals are referred to as different forms of severe malaria. Thus malaria parasites cause different kinds of illness in different people. 

The contributing reasons are because; the species of malaria parasite is important only P. falciparum causes severe disease in some people knowing that there are differences even between strains of P.falciparum in their capacity to cause disease; the immunity of the individual also affects how ill a person becomes when infected with malaria. The first patient described above was probably protected by immunity acquired slowly over years of repeated infection. It is also found that some people are genetically less susceptible than others to severe illness when infected with P. falciparum. Once severe malaria develops, extra facilities are usually needed to give the patient adequate treatment but in rural areas of Africa health infrastructures and facilities is not sufficiently developed which may lead to lose of life or disabilities (WHO, 1998).

        Clinical courses of malaria consist of bouts of fever accompanied by other symptoms and alternating with periods of freedom from any feeling of illness (Goettel, 1982). The life cycle of the parasites consists of an extrinsic phase in the invertebrate host of the anopheles mosquito and intrinsic phase in man that is divided into two; the erythrocytic schizogony in the liver cells and the erythrocytic schizogony in the red blood cells (Bahar, 1984). The female anopheline mosquito has been recognized as the vector of malaria.

        The anopheles belongs to the order of diptera, family culicidae and tribe anopheline. About 400 species of anopheles exist throughout the world, but only some 60 species are important vectors of malaria under natural conditions (Coluzzi, 1984). Development of the parasite that is contained in the saliva of the mosquito begins if a female anopheline mosquito bites an infected person, it injects the sporozites  into the blood stream of the human host and sucks the microgametocytes and macrogametocystes into its gut. These gametocytes develop into gametes in the gut of the mosquito. The microgametocytes mature by exglagellation and macrogametocyte develop into macrogametes with nuclei shifted to the periphery where projections are formed.

        Fertilization occurs when a microgamete penetrates the projections and a zygote is formed. Zygote gives rise to ookinete. After a period of 4-15 days after ingestion of gametocytes by mosquito, the oocyst mature with multiplication of nuclei and transformation of sporozoites depending on the temperature (Bukot, 1987). 

        Incubation period is the time between the infection and the first appearance of clinical signs of which fever is the most common (Sherman, 1998). The incubation period is usually between 9-30 days and varies with the species of the parasites (Shortest for P. falciparum longest for P. malariae ) this also depends on the circumstances of the infection, whether natural, by mosquito bite or artificial e.g by injection infected blood (WHO, 1983).    

        In the course of study, two or more parasites can be found in the human host blood and there is a tendency for one species of the parasites to predominate over the others. This is known as mixed infection. The most common types of mixed infection are P. falciparum and P. vivax in sub tropical areas while in tropical Africa P. falciparum and P. malaria are prevalent. Cerebral malaria is observed as caused by mixed infection (Lyn, 1987).     

        The modes of transmission of the disease include blood transfusion which does not involve the pre-erythrocytic and exo-erythrocytic stages. Malaria transmitted in this way is easily cured and does not involve relapses. Another process is by congenital transmission that is seen in pregnant mother to their child. The major mode of transmission is through the vector.

        The growth rate of the larva of mosquito determining transmission rate is directly proportional to the suitability of the environment to its requirement that vary from species to species (Thompson, 1996). In tropical Africa, the climatic condition favour an intense transmission of P. falciparum the prevailing parasite through mosquito vector of which the notorious and ubiquitous A. gambiae is the most important because of its wide distribution, breeding habits, large members and preference for human blood (Bruce, 1983).

        The epidemiological data reveal that malaria induced morbidity and mortality may vary considerably within a relatively small area (Olaleye, 1995). A prevalence of 90 % has been reported for wet season in Ebonyi State (Eneanya, 1998).
        The management of malaria by people dates back to the origin of malaria. In modern times managing malaria could mean treating the infection using antimalaria drugs, but the malarias parasite has proved a formidable adversary for medical researchers. Invariable it owes its success to the fact that it has chosen not to live as a free living organism but a parasite and has adapted to the host and its immune system (Nowikowski, 1987). Beside, vector resistance to insecticides, other factors that could possible influence malaria situation in a community include the development of resistance in P. falciparum to drugs (Nguyeh et al., 1982). 

Resistance of P. falciparum to drugs has become the most important threat to effective control of the disease. In Nigeria, there is paucity of information on studies on the malaria management of the poor. However various antimalarias abound, both local and scientific preparations are used by people. The introduction of insecticide treated nets (ITN) and the possibility of using vaccines helps a lot (Hira, 1987). The cost of treating malaria illness accounts for one-third cost of the illness, two-third reflect the time (Bonilla et al, 1992).
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