Malaria Transmission Dynamics in East Africa

Abstract

Malaria remains one of the deadliest mosquito-borne diseases in the world and indeed in sub-Saharan Africa and the sub-region of East Africa. The sub-region ranges from the coastal landscapes of Kenya and mainland Tanzania to the east borders of the congolian tropical rain forest and river basin on west Uganda boundary. The many water bodies in the region provide breeding grounds for Anopheles mosquitoes which transmit malaria affecting large populations of humans. Domestic animals and wildlife also play a pivotal role in malaria transmission by providing micro-breeding and resting sites via their footprints and sheds. The dynamics of transmission of malaria therefore include the presence and behaviors of the Anopheles vectors, the prevalence of the Plasmodium parasites, seasonality, climate change and related environmental factors favoring transmission in East Africa, and affected human hosts. Rainfall patterns and temperature stand out in affecting both the vector and malaria parasite life cycle. Inadequate use of preventive measures and treatment regimens has increased the risk of transmission of the parasites. This chapter explores the dynamics and trends of malaria transmission in this part of Sub-Saharan Africa.

1. Introduction

Malaria is still one of the deadliest mosquito-borne diseases in the world and has remained the cause of many infections and deaths in East Africa [1, 2]. There are approximately 3500 known species of mosquitoes worldwide. Among them, the genus of Anopheles mosquitoes transmits malaria in sub-Saharan Africa. This genus contains more than 460 recognized species, and approximately 60–100 Anopheles species have been implicated in transmitting malaria parasites [2, 3]. East Africa is indeed a sub-region of Sub-Saharan Africa and is endowed with a tropical climate, diverse landscapes, and remarkable ecological features that are conducive for spread of malaria. The sub-region encompasses a large area, extending from the coastal areas of Kenya and mainland Tanzania to the western borders of Uganda and east Congo River basin. The Great Rift Valley, a geological trench that traverses these countries, is composed of escarpments, volcanoes, lakes, and hot springs and a unique tropical biodiversity within which Anopheles mosquitoes flourish and spread malaria.

At the core of East Africa is Lake Victoria whose basin supports year round malaria transmission. The lake provides important freshwater resources and sustains the livelihoods of millions of people who due to exposure to malaria have diverted their economic development in terms of these resources needed for prevention and cure of the disease [4]. Other lakes in the sub-region which experience malaria transmission include Lake Tanganyika, Lake Malawi, and the numerous freshwater lakes located in the Great Rift Valley. Malaria thrives in such areas with stagnant water, which serve as breeding grounds for mosquitoes. The presence of these lakes and other fresh water bodies in lowlands and some highland areas of East Africa have contributed to the prevalence of malaria. The Anopheles mosquitoes concurrently find suitable habitats for breeding within their bounds [5].

1.1 Anopheles breeding and proximity to human populations

Anopheles mosquitoes breed in relatively clean stagnant or slow-moving water bodies including water storage tanks, temporary pools, streams, river bank vegetation shelters, rice irrigation fields, ponds and swamps which are widespread in the sub-region [6]. In urban areas, Anopheles mosquitoes tend to breed in artificial water containers, such as jerricans, barrels, and discarded items that collect water. These breeding sites are often found in close proximity to human residences. Moreover, poorly maintained drainage systems and improper waste management have created stagnant water pools suitable for mosquito breeding in most of these urban areas. In rural areas Anopheles mosquitoes breed in natural water bodies like streams, river banks, ponds, and swamps. These breeding sites are often located in close proximity to human settlements, particularly in areas where water sources are shared between the inhabitants and breeding by mosquitoes [7]. A case in point is the village communities living in vicinity of rivers and areas with rice irrigation fields in which the paddies provide breeding grounds for Anopheles mosquitoes. The many rice irrigation schemes in the sub-region have attracted huge settlements where immune and non-immune human populations provide labor in the fields and thereby come into close proximity of breeding sites of the Anopheles vectors of malaria.

Common human behaviors in East Africa such as storing water in containers or engaging in outdoor activities near water bodies creates additional breeding sites for mosquitoes unintentionally. Furthermore, settlement patterns in this region show a pattern of close proximity of houses to water bodies, which affects the distance between breeding sites and human populations. However, the specific distance between Anopheles mosquito breeding habitats and human populations differ widely and are determined by local environmental and socio-economic factors. The traditional east African type of house constructed in lowlands is mosquito permissive and contributes to massive entry of Anopheles mosquitoes into the houses mainly through the eyes and bite inhabitants without treated bed nets thereby increasing the chances of malaria infection.

1.2 Role of domestic animals

While humans are the primary hosts for malaria parasites, mosquitoes feed on both humans and animals, and some domestic animals have been found to contribute to the dynamics of malaria transmission in the region. Female Anopheles mosquitoes require blood meals to complete their reproductive cycle. Besides feeding on humans, they bite and feed on domestic animals, including cattle, goats, sheep, pigs and dogs. Domestic animals have indeed been implicated in influencing the abundance and density of Anopheles mosquitoes. Livestock, such as cattle and goats, provide blood meals for mosquitoes, which support their survival and reproduction. Areas of East Africa with higher livestock populations tend to experience increased mosquito densities, which subsequently elevate the risk of malaria transmission to both humans and animals [8]. Cattle require water for drinking, and their presence near water bodies have contributed to the creation of additional breeding habitats for Anopheles mosquitoes. Cattle troughs, footprints, watering holes, and areas where animals congregate providing suitable breeding sites for mosquitoes when the water becomes stagnant or poorly drained.

1.3 Vegetation cover

Vegetation, inclusive of forests, savannas, dense vegetation near water bodies, and maize plantations provide suitable breeding sites for Anopheles mosquitoes. These vegetation areas usually have natural depressions, puddles, whorled leaves or small pools of water that collect rainwater, creating stagnant water bodies where mosquitoes lay their eggs. High vegetation coverage near human settlements increases the likelihood of mosquito breeding sites in close proximity to human populations. Changes in vegetation coverage due to deforestation, land conversion for agriculture, and urbanization has contributed to mosquito breeding and malaria transmission. Deforestation, for example, has led to alterations in mosquito habitat availability, water availability, and human-animal interactions, potentially influencing the transmission of the disease [9]. The dynamics of the role of vegetation cover in Anopheles mosquito breeding depend on factors such as the prevalence of mosquito vector species, change in temperatures and variable rainfall patterns in the local habitats.

2. Components of malaria transmission dynamics

East Africa is known to have a high burden of malaria attributable to Anopheles mosquito vectors with several factors contributing to its transmission [10]. Malaria transmission dynamics in the sub-region is therefore characterized by the presence of the Anopheles mosquito vector species, the Plasmodium parasites that cause the disease, human host factors, and environmental factors including transmission seasonality and climate change [11].

2.1 Anopheles species and Plasmodium parasites

The primary mosquito vectors responsible for malaria transmission in East Africa are mainly Anopheles gambiae, An. arabiensis and An. funestus. These mosquito species thrive in the region’s diverse ecological backgrounds, including urban centers and rural areas of both lowland and highland settings. In Kenya, mainland Tanzania, and Uganda An. gambiae and An. funestus are the most efficient and widespread mosquito vectors. They breed in various water bodies, such as stagnant puddles, rice fields, irrigation channels, and river edges [11, 12, 13]. The most prevalent species of malaria parasites in the sub-region are Plasmodium falciparum, which is responsible for severe cases and most malaria-related deaths, and Plasmodium vivax, which is less common but still present in some areas. Plasmodium falciparum is the most deadly of all malaria parasites and is responsible for the majority of severe malaria cases and malaria-related deaths in East Africa [14]. It is known for its ability to rapidly multiply in the bloodstream and cause severe complications, such as cerebral malaria and severe anemia. Plasmodium vivax has the unique ability to form dormant liver stages, the hypnozoites, which can lead to recurrent infections even after successful treatment of the acute phase [15] thus propagating transmission further.

2.2 Human host factors

The risk of malaria infection is influenced by various human factors. These include individual immune responses, genetic factors, previous exposure to malaria, their behavior, nutritional status and travel among others. Vulnerable community members pertaining to severe malaria include young children, pregnant women, non-immune individuals and those with weakened immunity probably from malnutrition common in the region. With acquired immunity, those in the region living in endemic areas have developed partial immunity over time through constant repeated exposure to Plasmodium parasites. Among those living in endemic regions such as around Lake Victoria are cases of genetic variants of sickle cell trait that are less vulnerable to malaria infection. Behaviorally, there is a tendency for some people who live in areas with high mosquito density and have not embraced usage of repellents and mosquito nets risking being bitten by infected mosquitoes. With much poorly constructed homes and limited access to health facilities for diagnosis and treatment, malaria has remained a significant public health challenge in East Africa, leading to substantial morbidity and mortality, particularly among pregnant women and children under 5 years of age [12].

2.3 Transmission seasons and suitable conditions

East Africa’s diverse landscapes, from coastal regions to high-altitude areas, play a significant role in malaria transmission. Mosquito breeding sites, such as stagnant water bodies, are abundant, and suitable climatic conditions support the survival and reproduction of both mosquitoes and parasites. Kenya’s diverse climate, characterized by distinct wet and dry seasons, significantly influences malaria transmission patterns. In all other major East African Countries, there is an increase in mosquito breeding sites due to the accumulation of water during the rainy season. The high humidity and temperatures during this period accelerate mosquito development and the incubation of malaria parasites within the mosquitoes [16, 17, 18]. Malaria transmission in the region is seasonal, with peak transmission occurring during and after the rainy seasons when mosquito breeding sites increase. This seasonality leads to fluctuations in malaria incidence, with higher transmission rates during the wetter months. The availability of suitable breeding sites, especially during the rainy season, facilitates the rapid proliferation of these mosquito populations, leading to increased malaria transmission.

3. Underlying factors in malaria transmission

3.1 Malaria vector presence

In East Africa, several Anopheles mosquito species are known to be important vectors of malaria. The predominant species vary in different regions and over time due to various factors, including environmental conditions and human interventions. Precisely, the Anopheles mosquito species commonly associated with malaria transmission in East Africa are Anopheles gambiae complex and Anopheles funestus. The Anopheles gambiae complex contains multiple sibling species, including Anopheles gambiae and Anopheles arabiensis [19]. Anopheles gambiae is often the most important malaria vector in many parts of East Africa, while Anopheles arabiensis is also a significant contributor to malaria transmission. Anopheles funestus is found in various parts of East Africa and also plays a significant role in malaria transmission. The relative abundance and distribution of these species varies across different areas of the sub-region and may also change over time.

3.2 Distribution and density of Anopheles mosquitoes

The distribution of the various Anopheles mosquito species which are associated with malaria transmission in East African countries of Kenya, mainland Tanzania and Uganda include Anopheles gambiae, which is widespread in sub-Saharan Africa. Other countries in sub-Saharan Africa where An. gambiae is found are Nigeria, Ghana, Burkina Faso, Cameroon, and Sudan among others. Anopheles funestus is found in widespread areas of East Africa and extends further south in countries such as Mozambique, Malawi, Zambia, Zimbabwe, and parts of South Africa. Anopheles arabiensis is prevalent in sub-Saharan Africa, and includes Kenya and mainland Tanzania among others such as Ethiopia, Sudan, and Somalia. It is particularly known for its adaptability to arid and semi-arid environments. Anopheles merus is primarily found in coastal areas of East Africa, including parts of Kenya and mainland Tanzania. Anopheles coustani is not only found in East Africa but also parts of West and Central Africa. Anopheles rivulorum, a closely related species to Anopheles funestus is found in various parts of Africa, including East and West Africa. A new entrant species, Anopheles stephensi has recently invaded East Africa but is originally predominantly found in parts of Asia, including countries such as India, Pakistan, Iran, Iraq, Afghanistan, and Saudi Arabia [19]. These malaria mosquitoes exhibit some degree of geographic variation within their ranges and their distribution may not be limited to the countries mentioned above, as they may be present in neighboring regions.

Malaria transmission by Anopheles mosquito species in East Africa vary in density [20, 21, 22]. An. gambiae is often the most important vector in many parts of East Africa. It typically prefers breeding in sunlit water bodies such as small temporary pools, puddles, and agricultural fields. It is adapted to both rural and urban environments and exhibits a preference for biting humans. Anopheles funestus is another major malaria vector in East Africa, particularly in areas with higher rainfall and more permanent water bodies. It commonly breeds in large, permanent bodies of water like swamps, lakes, and rivers. It is typically more active during the early evening and late night hours, and it tends to bite both humans and animals. Anopheles arabiensis is known for its ability to adapt to various ecological settings. It exhibits a preference for breeding in temporary water bodies, including small rain pools, agricultural fields, and human-made containers. It is commonly found in rural areas and is often active during the early evening and early morning hours. Anopheles merus overall contribution to malaria transmission may vary depending on local conditions and its relative abundance compared to other species. Anopheles coustani plays a lesser role in malaria transmission compared to species like An. gambiae s.s. and An. funestus. It is more commonly found in savannah and grassland regions and exhibits a preference for biting both humans and animals [14].

3.3 Areas of high transmission of Plasmodium parasites

As depicted in Figure 1 the areas of high transmission for Anopheles mosquito species vary within East Africa depending on factors such as climate, geography, and local ecological conditions [24]. The precise distribution and intensity of malaria transmission may vary within these regions, influenced by factors such as climate variations, human population movements, and the prevalence of malaria parasites [14]. Warmer temperatures shorten the development time of the Plasmodium parasites within the mosquito, leading to increased transmission rates. Changes in rainfall patterns experienced in parts of East Africa are responsible for creation of breeding sites for mosquitoes, affecting their abundance. The high population movements including travel in East Africa, has introduced malaria infected individuals to new areas triggering outbreaks of malaria especially in highlands where many susceptible individuals live.

Figure 1.

Plasmodium falciparum parasite prevalence in East Africa [23].

The Entomological Inoculation Rate (EIR) referring to the number of infectious mosquito bites received by an individual per year is a crucial epidemiological measure used to assess the intensity of transmission of malaria. The EIR is higher in areas with high mosquito density, favorable breeding conditions, and high malaria prevalence in humans compared to areas with lower malaria prevalence [24, 25]. Anopheles gambiae is known to be highly efficient in transmitting malaria parasites, particularly Plasmodium falciparum, which remains the most common in the region and highly virulent. The EIR has been used in East Africa to gauge the risk of malaria infection faced by local populations. Surveys involving human landing catches and indoor mosquito trapping have been carried out to estimate mosquito biting rates and the proportions of mosquitoes infected with Plasmodium parasites [22, 26].

3.4 Prevalence and diversity of Plasmodium species

Malaria, caused by Plasmodium parasites, is a major public health concern in East Africa. The region is highly endemic for malaria, with transmission occurring throughout the year, although intensity may vary across different areas and seasons. The main species of Plasmodium responsible for malaria in East Africa is Plasmodium falciparum, which is the most virulent species and responsible for the majority of malaria-related deaths, and Plasmodium vivax, which is less prevalent but can cause relapses of the disease [24]. High parasite prevalence is bound to increase the chances of the Anopheles mosquitoes acquiring infection from human hosts during blood feeding and eventually transmitting it to other persons [27]. The prevalence of Plasmodium parasites in East Africa is influenced by several factors, including climate, geography, human behavior, and socioeconomic conditions. Malaria transmission is facilitated by the presence of competent mosquito vectors, primarily Anopheles mosquitoes, which breed in various types of water bodies, such as stagnant pools, swamps, and rice fields. The high humidity and temperature in many parts of East Africa provide favorable conditions for mosquito breeding and parasite development [28].

3.5 Seasonality, altitude and related factors

Seasonality, altitude, and other related factors play significant roles in malaria occurrence and transmission in East Africa [24]. Malaria transmission in East Africa often exhibits seasonal patterns, with higher transmission rates during certain times of the year. The exact timing and duration of the peak transmission season varies across different regions and countries. Generally, the transmission increases during or after the rainy season when there is an abundance of mosquito breeding sites. The rainy season provides optimal conditions for mosquito reproduction and survival, leading to increased malaria transmission. However, in some areas with irrigation schemes or areas with perennial transmission, malaria may occur throughout the year [13, 29]. Altitude has a significant impact on malaria transmission in East Africa. Generally, malaria transmission decreases as altitude increases. This is because the Anopheles mosquitoes, which are the primary vectors for malaria, have specific altitude preferences. These mosquitoes thrive in low-lying areas and are less common at higher altitudes due to the cooler temperatures and less favorable environmental conditions. Therefore, highland areas in East Africa, particularly those above 2000 meters, tend to have lower malaria transmission rates compared to lowland areas.

Several other factors influence malaria occurrence and transmission in East Africa, including vector species, climate change and socioeconomic factors. The presence and abundance of specific mosquito vector species may affect the transmission dynamics. Different Anopheles mosquito species have varying preferences for breeding sites, feeding behavior, and susceptibility to Plasmodium parasites. Human activities, such as agricultural practices, deforestation, and settlement patterns, have an impact on malaria transmission. Changes in land use and water management practices may create or modify mosquito breeding sites, increasing the risk of malaria transmission. Climate variability and change may influence malaria transmission patterns in East Africa. Changes in temperature, rainfall patterns, and humidity levels may impact mosquito breeding, parasite development, and the geographic distribution of both the vectors and the parasites [30, 31]. Poverty, limited access to healthcare services, and inadequate infrastructure may contribute to the persistence and burden of malaria. These factors may affect the availability and utilization of preventive measures, diagnosis, and treatment options, leading to higher malaria transmission rates [25]. The specific influence of these factors may vary within different countries and regions of East Africa.

4. Malaria transmission trends

Figure 2 depicts general trends of malaria transmission in East Africa. The transmission in the region is a complex interplay of various factors, including an enabling environment and habitats for breeding consisting of suitable water bodies, landscapes, vegetation, altitude and the phenomena of climate change. The conducive breeding environment yields three efficient vectors of malaria: Anopheles gambiae, An. funestus, and An. arabiensis among others. Due to their efficiency, female Anopheles mosquitoes infected with Plasmodium parasites from a previous human blood meal develop a tight relationship in which the parasites undergo sexual reproduction, fertilization and develop from zygote into ookenetes in the midgut and migrate to the body cavity as oocysts which multiply and rupture to release sporozoites. The sporozoites migrate to the salivary glands. At the next available blood meal, the mosquito vectors pass on the infective sporozoites into a new human hosts’ blood and into the liver in form of merozoites. Merozoite introduction into the bloodstream causes malaria. Both human and domestic animal hosts interact with the environment in a delicate balance where if not treated, newly emerged adult females acquire parasites afresh from infected individuals and the transmission continues unabated.

Figure 2.

Malaria transmission in East Africa (by author).

In order to determine the level of infection in relation to transmission of malaria in East Africa, various methods and data sources may be employed to provide data on prevalence rates, transmission intensity, and intervention efforts in the region. Existing data sources and detailed reports on malaria transmission are available with organizations such as World Health Organization (WHO), Centers for Disease Control Malaria Information and the Malaria Atlas Project (MAP) [32, 33, 34]. The Lake Basins and the coastal regions in East Africa are endemic for malaria. These regions experience higher transmission rates of malaria attributed to the climate and vector abundance. To provide insights into reported malaria cases from local health facilities and determine trends and prevalence rates of malaria, analysis of epidemiological data from surveillance systems is procedural contributing to determination of the level of infection. Alongside, vector surveillance is often conducted to assess vector abundance and Anopheles distribution in the region. Monitoring Anopheles presence and behavior is crucial for understanding transmission patterns [35, 36, 37].

Blood sampling and laboratory analysis is carried out in local laboratories to measure Plasmodium parasite prevalence and to determine the prevalence of malaria parasites among human populations in the region through conducting surveys in affected areas [38]. Interventions such as Long Lasting Insecticide Nets (LLINs), Indoor Residual Sprays (IRS) and administration of malaria drugs are assessed to help determine the existing level of transmission and gauge their impact [39]. Collaboration between researchers and local health authorities is crucial in providing and updating data on insights on the overall levels of infection [27].

5. Role of interventions and challenges

Interventions have mainly aimed at controlling Anopheles mosquitoes using (LLINs) and IRSs, preventing the spread of Plasmodium parasites, and reducing incidence of the disease through improved access to diagnostics and treatment. Long-lasting Insecticide Nets have proved effective at protecting individuals during sleep while IRS has targeted high transmission areas where Anopheles mosquito densities are high. These interventions are proving successful in some areas of East Africa, but there are challenges and limitations experienced regionally that lead to their limitation in impacting reduction in malaria transmission.

5.1 Transmission persistence

Emergence of insecticide-resistant Anopheles mosquito populations is widespread in the region attributed to pyrethroids used in LLINs and IRS programs. This has led to interventions becoming less effective in controlling the mosquito populations and gradually malaria transmission has persisted in areas where insecticide resistance is prevalent [26, 40, 41]. The malaria parasites have also developed resistance to treatment by some anti-malarial drugs such as chloroquine, which hampers the effectiveness of treatment interventions and further translates into persistence of malaria in the local population. High transmission of malaria is evident in some remote and impoverished areas of East Africa where access to healthcare facilities for treatment is lacking and people are often not diagonized and prescribed appropriate antimalarial drugs. Delayed or inadequate treatment has contributed to resistant forms of malaria and persistence of transmission in the region.

The East African Community has embraced population movement for economic enhancement; however, this movement has contributed to the spread of malaria into new horizons or into areas where the disease had been controlled. Such movement and other behavioral tendencies including outdoor activities during peak mosquito biting hours of evening and early in the morning expose people and increase the risk of mosquito bites and subsequent malaria infection. In some cases misconceptions about malaria prevention and treatment contributes to delays in seeking appropriate healthcare, aggravating transmission [42]. Lack of community acceptance of an intervention due to local beliefs has hampered success of some interventions. For instance, inconsistent use of bed nets and failure to adhere to treatment regimens reduces the impact of these interventions and provides for further transmission. Factors such as socio-economic status, education, cultural superstitions and practices influence the uptake of these interventions [43].

5.2 Changes in climate

Changes in climate have influenced mosquito breeding patterns and spread of malaria. Climate change has resulted in the expansion of geographical ranges of Anopheles mosquito vector populations and Plasmodium parasites, contributing to persistent transmission. Climate Variability has affected mosquito breeding habitats and influenced the distribution and abundance of Anopheles mosquitoes. Changes in temperature and rainfall patterns create new opportunities for mosquito breeding and alter the timing of peak transmission seasons [44]. Temperature affects both the Anopheles mosquito and Plasmodium’s life cycle in the vector. The daily temperature variation influences the survival, development, and reproduction rates of mosquitoes. Stagnant water after increased rainfall provides ideal conditions for mosquito larvae to thrive. Humid conditions and elevated temperatures in the region result into faster development rates for the mosquito from egg to adult, which translates into more rapid population growth. Due to the foregoing climatic changes the extrinsic incubation period, which is the time required for Plasmodium parasites to complete development within the malaria mosquito before transmission to a new host, is shortened thereby perpetuating transmission.

5.3 Vector behavior and outdoor transmission

In areas of high bed net coverage, Anopheles mosquitoes in East Africa have exhibited changes in their feeding behavior, with an increasing proportion of bites occurring outdoors and at times when people are not protected by bed nets [45]. This behavioral resistance reduces the effectiveness of indoor-based interventions leading to residual malaria transmission. Research and surveillance efforts have been hampered in the absence of understanding the behavior of outdoor biting mosquitoes. Outdoor resting sites for Anopheles mosquitoes have created alternative breeding and resting sites, a pattern that continues to contribute to transmission in the absence of wearing protective clothing and using repellents, especially during times when bed nets may offer limited protection.

5.4 Sub-optimal implementation of integrated strategies

Lack of integration of interventions hinders their effectiveness when they are implemented in isolation [46]. A case in point in the region is when vector control measures in some areas are not accompanied with case management propagating transmission rates due to untreated cases alongside concurrent mosquito breeding. Limited impact on transmission is also evident when mosquito behavior, human behavior and changes in environmental conditions are not addressed in combination leading to suboptimal results. The risk of resurgence in cases of malaria is imminent in the region without a comprehensive approach in implementing interventions. Focus on one intervention is the cause of emergence of resistant Anopheles mosquitoes and Plasmodium parasites in some areas of East Africa which continues to reduce the long-term effectiveness of interventions [47].

6. Conclusion

Malaria, a life-threatening mosquito-borne disease caused by Plasmodium parasites, continues to be a major public health concern in East Africa. The region, comprising of the countries Kenya, mainland Tanzania, and Uganda, is characterized by ecological features, a typical tropical climate and landscape endowed with the Great Rift Valley, lakes and lake basins which contribute to creation of breeding habitats for Anopheles mosquitoes. Most of these areas are relatively close to human dwellings. The proximity of Anopheles mosquito breeding habitats to human populations varies depending on the specific geographic location and local conditions. In general, Anopheles mosquitoes tend to breed in areas near human settlements both in urban and rural settings and take advantage of readily available blood meals. The main vectors of malaria, which are Anopheles gambiae and An. funestus and An. arabiesis, transmit the causative parasites particularly Plasmodium falciparum and to a lesser extent, P. vivax. Specific mosquito species’ presence and abundance varies within countries depending on local environmental factors. The transmission dynamics of Anopheles mosquito species are influenced by factors such as vector behavior, ecology, vector control interventions, host availability, and the prevalence of malaria parasites within the human population.

The contribution of domestic animals to Anopheles mosquito breeding and malaria transmission depends on local conditions, such as vector species, animal husbandry practices, and malaria prevalence in both humans and animals. Factors such as population movements, inadequate healthcare infrastructure, poverty, and limited access to effective prevention and treatment measures contribute to the persistence of malaria in the region. Efforts to interrupt malaria transmission in East Africa target both the mosquito vectors and the human hosts. Human behavior significantly impacts malaria transmission in the region. Outdoor activities during peak mosquito biting hours and inadequate use of preventive measures, such as insecticide-treated bed nets, increase the risk of mosquito bites and subsequently lead to malaria infection.

The climate, especially rainfall patterns and temperature affects both the mosquito and the malaria parasite’s life cycle. Rainfall patterns affect the availability of breeding sites for mosquitoes when stagnant water from rainfall provides ideal conditions for mosquito larvae to thrive. The daily temperature variation influence their survival, development, and reproduction rates with higher temperatures leading to faster development rates of mosquitoes from egg to adult, resulting in more rapid mosquito population growth. Daily temperature variations also influence human behavior pertaining to use of bed nets where people may be less likely to sleep under bed nets during hot nights, leading to increased exposure to mosquito bites.

The sub-region faces several challenges in its efforts to control malaria. These challenges include the emergence of drug-resistant malaria parasites, insecticide-resistant mosquitoes, inadequate healthcare infrastructure, and limited resources for implementing comprehensive control programs. The lack of awareness about malaria prevention and treatment measures may also lead to delays in seeking appropriate healthcare, further exacerbating the disease’s transmission. Overcoming these intervention challenges requires collaboration among researchers, policymakers, and local communities to develop context-specific and sustainable approaches for malaria control in East Africa. Additionally, continuous monitoring and adaptation of strategies are essential to address evolving challenges and ensure progress toward malaria elimination goals.

Acknowledgments

I acknowledge the support by my employer, Jaramogi Oginga Odinga University of Science and Technology (JOOUST), especially financially and granting me a portion of time within which I was able to contribute this chapter. I also wish to acknowledge the authors led by Victor A. Alegana for utilizing their map of Plasmodium falciparum prevalence in East Africa. I thank Wendy P.L.A. Davis for the thorough editorial work she rendered to this chapter.