A Hospital Based Study Of Malaria
[IN NDIEGORO COMMUNITY, ABA SOUTH L.G.A. ABIA STATE]

CHAPTER TWO
LITERATURE REVIEW
2.1    GEOGRAPHICAL  DISTRIBUTION
P. falciparum is found mainly in the hotter and more humid regions of the world. It is the main species found in tropical and subtropical Africa and parts of Central America and South America, Bangladesh, Pakistan, Afghanistan, Nepal, Sri Lanka, Southeast Asia, Indonesia, Philippines, Haiti, Solomon Islands, Papua New Guinea and many islands in Melanesia. It also occurs in parts of India, the Eastern Mediterranean and Middle East.Plasmodium falciparum is the most commonly encountered species in West Africa including Nigeria (Seboxa and Snow,1997; Mbanugo and Ejims,2000; Aribodoret al; Asianyaet al,1999)
P. vivaxis capable of developing in mosquitoes at lower temperatures than P. falciparum, and therefore has a wider distribution in temperate and subtropical areas. P. vivax is the main Plasmodium species in South America, Mexico, the Middle East, India, Pakistan, Sri Lanka, Papua New Guinea and Solomon Islands. It is also found in parts of Southern Asia, Indonesia, Philippines, Madagascar, tropical and subtropical Africa, china and Korea.
P.malariae has a much lower prevalence than P. falciparumand P. vivax. It accounts for up to 25% Plasmodium infection in tropical Africa. It is also found in India, Guyana, Malaysia and Sir Lanka. In these countries, it accounts for less than 10% of Plasmodium infections.
Plasmodium ovale has a restricted distribution and of low prevalence. It is found mainly in West Africa where it accounts for up to 10% of malaria infections. It has also been reported from other parts of the Far East, South East Asia and South America.
2.2    EPIDEMIOLOGY OF MALARIA
The setbacks in attempts at malaria eradication have led to renewed interests in the epidemiology of malaria. Various factors interplay to determine the two epidemiological extremes of malaria, that is, stable and unstable malaria. Such factors include environmental (or climatic), vectorial, parasite and host factors and failure of control policies. Malaria not only increase malaria- specific morbidity and mortality but also affect the general health of the population. Many malaria epidemics coincide with periods of famine, economic meltdown, war or civil disturbances involving impoverished populations that are often affected by other disease as well. The greatest consequences of malaria cases in many parts of the world stems in large part to these economic and human factors (Dick, 1985).
2.2.1    Environmental factors
The potential of the mosquito to serve as a vector depends on the ability to support sporogony, mosquito abundance, and contact with humans, which are all influenced by climatic and ecological factor. Temperature and mosquito longevity are other key factors affecting the parasite’s interaction with the vector. Development of P. falciparum requires a minimum temperature of 200C, whereas the minimum temperature for the other species is 160C. Temperature also affects the time of development in that the duration of sporogony is shorter at higher temperatures. A shorter duration of sporogony increases the chances that the mosquito will transmit the infection within its lifespan .Climatic factors such as; altitude, temperature and rainfall and breeding places also affect mosquito density. Small increases in existing low temperatures have been shown to exert a strong effect on increased transmission of malaria (Bradley, 1993; Lindsay and Birley, 1996).In a site situated at 2000m in western Kenya, malaria cases steeped when mean monthly temperature exceeds 18C and rainfall greater than 1500mm per month(Malakootiet al, 1998).Wet and humid environments provide the breeding sites and prolong the life of malaria vectors (Lindsay and Birley, 1996). These optimum conditions occur through out the year in most part of Nigeria and hence the prevalence rate is fairly constant throughout the year in both urban and rural areas. At high altitude, prevalence rate of malaria is low and no transmission occurs at 600 feet above sea level(Taylor and Mutambu, 1986).
2.2.2    Vectorial Factors:
The Mosquito (Anopheles spp.)
These are behavioral factors and susceptibility to infection. Some species of Anopheles are anthropophilic (prefers human blood), others zoophilic (prefers animal blood); some prefer to bite indoors (endophagy), others outdoors (exophagy); some prefer to rest during the day indoor(endophily), others out doors (exophily). Malaria vectors bite between dusk and dawn and generally choose well-oxygenated water rather than stagnant polluted pools to lay her eggs.
Anopheles gambiae, Anopheles arabiensis and Anopheles funestustransmit most of human malaria and are all found in Africa (Besanskyet al, 2004). An. gambiae, the most famous and significant of the three, is one of sixty anopheline mosquitoes able to transmit malaria to humans (Budiansky, 2002). An gambiaeis the primary malaria vector, this can be attributed, in part, to its relatively long life strong anthropophily and endophily.Their larvae tend to develop in temporary water bodies, such as those typically found near agricultural sites or even in flooded hoof print (Vogel, 2002). All these characteristics combine to make An. gambiaethe mostsuccessful vector.
2.2.3    Host Factors:
The following human factors influence the epidemiology of malaria: genetic, immune, nutritional and behavioral.
Behavioural Factors: