**1. Introduction**

Malaria itself or a disease looks like malaria has been distinguished before 4,000 years. The term *malaria* was derived from two Italian words "*mala aria*" meaning foul or bad air [1]. This name is originated from the observation that malaria cases were prevalent in areas where there is bad air associated with the accumulation of pools [2]. Malaria is caused by the genus *Plasmodium* (mosquitoborne apicomplexan parasite). At the time of bite by infected female *Anopheline* mosquitoes, this protozoal blood infection become conveying from one person to the next person [3, 4]. According to Miller *et al.* [5], malaria is expressed as a disease caused by repeated life cycle of the *Plasmodium* in the red blood cell. It is also defined as an illness brought by a parasite that lives some of the life in humans and some in mosquitoes [6].

The causative agents for malaria infection are among the genus *Plasmodium*, phyllum *Apicomplexa*, class sporozoa, family *Plasmodidae* and order Haemosporidia [7]. *Plasmodium* is considered to be instigated from photosynthetic protozoa, which is known as dinoflagellate. Among more than 200 different *Plasmodium* species, around 14 species are pathogenic to humans [8, 9]. The remaining species affect animals, such as rodents, monkeys and reptiles [10]. Five of the human pathogens, *P. ovale* sub-species (*P. ovale curtisi* and *P. ovale wallikeri*), *P. falciparum, P. vivax* and *P. malariae* are well known etiologic agents for human malaria. Infrequently, we could be naturally or accidentally infected by many simian species including *P. knowlesi*, *P. cynomolgi, P. bastianelli, P. brasilianum*, *P. schwetzi* and *P. inui*. Disease with *P. knowlesi* happens in individuals if an *Anopheles* mosquito previously diseased by a monkey malaria parasite bites humans. Incubation period (the time between the bite of mosquito and developing malaria symptoms) for falciparum*,* vivax and ovale*,* and malariae is 12, 14 and 30 days, respectively. But infections by *P. malariae* can exist in the blood for a very long period, may be decades, without ever producing symptoms. A person with asymptomatic (no symptom) *malariae* infection, however, can infect others, either through blood donation or mosquito bites. Incubation period is different for different persons and depends on the amount of the parasite involved [11–13].

Malaria is widely distributed throughout tropical regions in Africa, Asia, Hispaniola (Dominican Republic and Haiti), Central and South America, the Middle East and Oceania. The global prevalence of malaria species differs. *Falciparum* and *vivax* malaria pose the greatest public health challenge. *Falciparum* is mainly prevalent on the African continent and in the World Health Organization (WHO) regions of South East Asia, the eastern Mediterranean and Western Pacific. It is responsible for most deaths from malaria. *Plasmodium* parasites are affected by temperature. The development of *Plasmodium* species become slows as the temperature drops. When the temperature drops below 60°F, *P. vivax* totally stops developing. *P. falciparum* can regrate to develop at a bit elevated temperatures. This effect elaborates why malaria parasites are present in temperate environments. *Vivax* has a wider geographic distribution since it can grow in its vector at lower temperatures, cooler climates and elevated altitudes. However, *vivax* is more common in the Indian subcontinent and Central America. Despite it occurs in over all Africa, the risk of *vivax* infection is relatively low there due to lack of Duffy gene in most people of Africa [6, 14]. But, there is a supporting facts that *vivax* can be transmitted to negative Duffy blood group residents in Africa including Ethiopia [15]. South America and South East Asia have both *falciparum* and *vivax* species. *P. ovale* has an unusual distribution (present in West Africa, New Guinea and Philippines). Although, *malariae* has been wiped out from temperate climates, it persists in African sub-region [16]. *P. knowlesi* occurs in South East Asia with cases widely distributed in Sabah and Sarawak in Malaysian Borneo, and peninsular Malaysia. Cases have been reported from a number of other countries in South East Asia, and in travelers [12].

Mosquitoes of the genera Culex, *Anopheles*, Mansonia and Aedes may act as malaria vectors [16]. Nonetheless, malaria is transmitted mainly via the bite of *Anopheles* mosquitoes, which comprise 537 known species and majority (87%) of them have been formally named [17]. Nearly, 70 of these species are able to transmit *Plasmodium* parasite to human hosts and 41 of 70 are considered to be dominant vector species [1]. *Anopheles gambiae* and *A. funestus* are the most efficient vectors of malaria in the world. They are also the primary vectors of malaria in Africa [18]. In Ethiopia, two primary vectors of Africa and *A. pharoensis* are recognized as the dominant malaria vectors [15].

While some species grow in temperate climates and even continue to exist in the Arctic summer, majority of *anopheline* mosquitoes survive in tropical and subtropical regions. It was believed that *anopheline* mosquitoes are not breed on altitudes

#### *Malaria: Introductory Concepts, Resistance Issues and Current Medicines DOI: http://dx.doi.org/10.5772/intechopen.98725*

higher than 2,000 to 2,500 m. In this geographical boundary, there are a lot of malaria free places as its transmission is extremely reliant on the local environment and epidemiologic situations. *Anopheline* mosquitoes prefer comparatively clean water as their larval habitat (site for egg-laying and development of larvae) though species vary in the quantity of salinity and organic content and amount of sun exposure and temperature they prefer in their breeding sites. For example, city conditions can generate new spaces to mosquito larvae for development. Agricultural activities can also affect breeding site of mosquitoes. While the draining and drying of swamps removes the breeding areas of larvae, water-filled irrigation ditches could provide mosquitoes a new site for breeding. Egg, larva, pupa and adult (imago) are the four developmental phases of *anopheline* mosquitos. Adult males copulate to females in flight to provide adequate sperm for all subsequent egglaying. To develop the first batch of their eggs, adult females require at least 2 blood meals but one blood meal is enough to develop each successive batch. As development of egg needs around 48 h, blood-seeking is recurring every two to three nights. Under most favorable conditions, the average lifetime of the female (adult) *anopheline* mosquito is equal to or more than three weeks. External factors including temperature, moisture and natural enemies could decrease its prolonged existence. Adult males, in contrast, generally live a few days. If the mean ambient temperature goes beyond 35°C or humidity drops below fifty percent, longevity is drastically decreased, directly affects malaria transmission. In most tropical regions, cases of malaria become increased at the time of rainy season as the rainfall expands breeding grounds. The adult male *anopheline* feeds on nectar, while the adult female feeds primarily upon blood of warm-blooded animals, predominantly mammals. Some female *anopheline* mosquitoes that have a preference toward humans are termed *anthropophagic* (*anthropophilic*). Others who choose animals, such as cattle, are expressed as *zoophagic* (*zoophilic*). The interval over which a mosquito is attracted to its favorite source of blood usually ranges 7–20 m. Many *Anopheles* mosquitoes are either nocturnal (active at night) or crepuscular (active at dusk or dawn). Some are endophagic (feed indoors) while others are exophagic (feed outdoors). After blood feeding, some of them wishs to rest indoors (endophilic) while others intended to rest outdoors (exophilic) [6, 19, 20].

Mentioned earlier, malaria is transmitted from one individual to the next individual via the bite of female *Anopheles* mosquito that has been acquiring the parasite from the first person. The female mosquito needs blood protein for her egg maturation. *Anopheles* mosquitoes are attracted to human by a number of factors (for example heat, odor and exhaled carbon dioxide) and usually bite us between sunset and sunrise [12]. Since *Plasmodum* resides in red blood cells, malaria is also transmitted via donation of blood, transplantation of organ and sharing of needles or syringes contaminated by infected blood. A new born child could also acquire congenital malaria from her/his mother before/during birth [11, 21]. Rarely, accidental nosocomial (hospital acquired) transmission of malaria may occur, for example, where there is a breach in infection control or as a result of a medical procedure [12, 22]. Moreover, transmission of malaria can largely be affected by global warming [23, 24].

Cases of malaria occur in non-endemic areas without an apparent travel history is known as **cryptic malaria**. If the conditions are appropriate for the transmission cycle of *Plasmodium* to be maintained, periodic (sporadic) outbreaks of locally acquired malaria may occur when an imported malaria case happens in a non-endemic district and is bitten by a malaria vector that can transmit parasite to another person. This is called **introduced malaria**. This is generally results in a small cluster of 1 or 2 cases even though larger outbreaks may sometimes occur. If the environmental (climatic) conditions allow, malaria may also occur if a person

is bitten with infected mosquito that has been imported to a non-endemic region. This can be occured around airports (**airport malaria**) or from a mosquito that has stowed away in hand luggage (**baggage** or **luggage malaria**) if aircraft have not been disinsected in a well manner [12].

Chills, high fever, malaise, headache, muscle aches and sweating are the most frequently reported symptoms of malaria infection. The current diagnostic methods used for identification of *Plasmodium* species from blood samples are light/ fluorescence microscopy (gold standard method), immuno-chromatographic lateral flow assays (RDTs-rapid diagnostic tests), serology tests, and nucleic acid amplification techniques including PCR (polymerase chain reaction) and isothermal amplification [25]. Rolling circle enhanced enzyme activity detection (REEAD) and micromagnetic resonance reflaxometric (MMR) tests are recently developed parasitological methods appropraite for utilization in field detection of malaria infected individuals for population screenings [26].

Around 44% of world population is at risk from malaria [27]. The risk varies according to season, geographic location, activities, type of accommodation, and the use of malaria prevention drugs and bite avoidance measures. Approximately 229,000,000 cases of malaria, most (94%) from the WHO African Region, are taken place globally in 2019. The disease was caused 409,000 deaths worldwide and most (94%) of which are also from the African Region. Most cases of malaria in Africa are resulted from *P. falciparum*. In 2019, global case incidence and mortality rate of malaria was reduced by 57 and 10%, respectively. Malaria continues to strike hardest against children and pregnant women in Africa. Children aged <5 years are the most exposed group affected by malaria, accounted 67% of global malaria deaths in 2019 [28]. In the USA, roughly 1,500–2,000 cases of malaria in recent travelers are reported every year. Pregnant mothers have high vulnerability to *falciparum* malaria. *P. falciparum* malria contributes 8 to 14 percent low birth weight in malaria-endemic areas, which in turn minimize the likelihood of a baby's survival [19].

All travelers visiting malaria endemic regions are at risk of acquiring malaria. Certain travelers including pregnant women, children, older travelers, immunosuppressed individuals, those with an absent or dysfunctional spleen, and those with complex co-morbidities are at high risk for severe disease if they have malaria. As they are peculiarly attractive to mosquitoes and have high risk of developing severe infection with increased risk of death compared to non-pregnant mothers, pregnant women should be advised to stay away from (not travel to) malarious areas. Travelers who lost their spleen or travelers who have severe impairement of spleen are at particular risk of severe malaria and are advised to avoid travel to malarious areas. If travel is essential, antimalarial drugs are advised in both high and low risk areas, together with rigorous bite avoidance and awareness of the need for prompt medical attention if symptoms develop [12].

Malaria endemic regions are classified into stable and unstable malaria transmission areas. In stable regions, for example in most of sub-Saharan African countries, transmission of malaria is year-round with high infection rates. The population, predominantly adults, may therefore develop a degree of immunity with the majority of clinical cases occurring in infants and children. In unstable regions such as India, malaria transmission has a tendency to be seasonal with short epidemics of varying intensity. Transmission of malaria in these unstable regions is less sustained, hence the communities have weak immunity and all age categories may be affected [12]. In addition to health related impacts, there is a severe burden on economic setors in terms of lost days of labor due to the disease. In fact, malaria is considered to take off 1.3 percent from the economic growth and 40 percent from public health costs of some African countries. It also affects developing nations in most aspects including determent of tourism [29].

#### *Malaria: Introductory Concepts, Resistance Issues and Current Medicines DOI: http://dx.doi.org/10.5772/intechopen.98725*

Malaria is one of the major infectious diseases in Ethiopia [30, 31]. *Falciparum* and *vivax* are the main two species found in Ethiopia, accounting for 60% and 40% of malaria cases, respectively [32]. *Falciparum* has been the major cause of epidemics, and of most malaria deaths [33]. In Ethiopia, the epidemiological pattern of malaria transmission is generally unstable and seasonal; the level of transmission varies from place to place because of differences in altitude and rainfall patterns [32]. Depending on these rainfall patterns, transmission tends to be highly heterogenous geo-spatially within each year as well as between years [34]. Changes have been observed in the epidemiology of malaria through time. Global warming (changes in climate) are likely to lengthen the transmission seasons of important vector-borne diseases like malaria and to alter their geographic range [35]. Previously, malaria was known to occur in areas below 2000 m but currently it has been documented to occur indigenously even in areas above 2400 m, such as Addis Ababa [32]. Months from September to December and June to August are high malaria transmission seasons in Ethiopia. About 30,485,416 Ethiopians are living at high risk places for malaria infection. In 2019, 213 deaths and 904,496 confirmed cases due to malaria were reported by Ethiopian Federal Ministry of Health (FMoH) [25, 28]. Despite decreased malaria occurrence rate and death rate in Ethiopia since 2010 [28], high prevalence was observed in some areas in contrast to high household coverage of control interventions [36, 37]. This increment may be associated with individuals having poor socio-economic status [38]. Ethiopia has achieved only half of the millennium development reduction target of malaria. For this reason, the country must strengthen its malaria control and treatment approaches to attain the sustainable development goals [39].
