The aim in this chapter is to present an overview of the epidemiology of malaria. We present a summary of its transmission cycle. The clinical manifestation of the disease is described. The effects of climatic factors on malaria are discussed. The burden of malaria is discussed with more emphasis on Africa. It is seen that malaria has a harmful effect on the economic growth in the affected countries. Burundi is one of the world's most affected countries by malaria; we present some potential explanations of this situation.
Malaria, the disease
Malaria is the most prevalent mosquito-transmitted disease in the world. Each year between 300 to 500 million people are infected by this disease, and 1 to 2 million die from it [1]. Malaria is caused by a parasite of genus plasmodium from female mosquito. The four species of Plasmodium are plasmodium falciparum, plasmodium malariae, plasmodium ovale and plasmodium vivax [2,3]. In Africa the predominant species of malaria parasite is plasmodium falciparum. A person becomes infected when he is bitten by a female Anopheles mosquito which has previously been infected. Uninfected Anophele mosquito becomes infected when it bites an infected person. When a mosquito bites an infected person, a small amount of blood which contains microscopic malaria parasites is taken in. The parasites grow and mature for some days, then travel to the mosquitos salivary glands. When the mosquito next takes a blood meal, these parasites mix with the saliva and are injected into the bitten person [2]. The incubation period of the parasite in the vector takes 13 days to complete at 24C for Plasmodium falciparum [2]. Malaria is therefore closely bound to the conditions which facilitate the survival of the mosquito such as habitat and breeding sites and which favor the life cycle of the malaria parasite by providing suitable temperatures[4]. Researches on the epidemiology of malaria suggest that these conditions are determined by climatic and environmental factors.
Malaria is a serious and often fatal disease. However, the disease is not contagious, and cannot be transmitted from person to person like the flu. The most dangerous form of malaria is caused by Plasmodium falciparum, which if it's not treated, can cause anemia, jaundice, kidney failure, seizures, coma, and death. In fact, plasmodium falciparum kills up to 40% of the infected persons [5]. Approximately 90% of all deaths due to malaria occur in Africa [6, 7]. Major factors that are responsible for this high mortality from malaria in Africa include poor access or lack of health services, low quality of health care, and the increased resistance of malaria parasites to the most used and affordable first-line drugs such as chloroquine and sulphadoxinepyrimethamine in some countries [8, 9]. Moreover, the successful elimination of malaria from most part of Europe and North America and the failure of the global malaria eradication programme led to a loss of interest in fighting malaria for a period of more than 25 years from the early 1970s to the late 1990s. For instance, only 3 of 1.223 new drugs developed during the period 1975-1996 were antimalarials [10]. Industries lost interest in developing insecticides for public health use and there have been a decline in supporting research on malaria. Furthermore, in many malaria-endemic African countries, national malaria control programmes which were initiated during the colonial period and supported during the period when a successful elimination of malaria was considered to be possible, collapsed [11]. Another very important factor is the suitable climate to malaria transmission.
Clinical manifestations
Clinically, malaria manifests itself in its mild form as a febrile illness associated with
other non-specific symptoms[12]. The first clinical signs of the disease will appear after the incubation period, which varies between nine and fourteen days for falciparum malaria. Clinical diagnosis is usually confirmed by a blood test, involving microscopic evidence of parasites in the blood, or by some rapid diagnostic kit [13]. Once transmitted to human the parasite invades the liver and red blood cells, affecting the blood flow to vital organs. The head, the muscles and body ache, the patient has fever, sweats, shivers and sometimes vomits [2]. Acute and chronic malaria infections can alter the immune system and the body's response to vaccines, and increase vulnerability to other infections. Furthermore, chronic malaria is an important causal factor of anaemia [14,15], which has been shown to have direct physical effects, lowering worker productivity and output[16,17].
Climatic influence on malaria
Temperature is a very important environmental factor that influences malaria transmission. Anopheles mosquitoes need temperatures between 25°C and 27°C for optimum breeding, feeding, and cellular metabolism. Likewise, warm temperatures are also crucial for the development of the Plasmodium parasite. In this case optimal temperature is be between 20°C and 30°C [18]. The effect of an increase in temperature on the parasite is to shorten the sporogony (reproduction process) cycle and hence to accelerate transmission. Increasing temperature also increases transmission by increasing the frequency with which the vector takes blood meals, which increases the growth rate of vector populations through shortening of the generation time[18]. Higher temperatures reduce the longevity of adult vectors, and hence fewer of them will survive the sporogony cycle to become infective. There are thus upper and lower thresholds outside which malaria transmission is very inefficient or impossible. Below 16°C parasite development ceases. The intensity with which malaria is transmitted often depends on the minimum and maximum temperature ranges in which the vector and parasite reside [18,19].
Another factor influencing the multiplication of mosquitoes is rainfall. Mosquitoes breed in water. Therefore, right quantity of precipitation is required in order for the mosquito to complete its life-cycle. Too much, or too little rainfall have negative impact on mosquitoes population. In general, rainfall needs to be in the range of 50mm and 80mm each month to create of adequately-sized pools of standing water [20]. Increasing rainfall and vegetation density generally have a positive impact on malaria transmission through the provision of breeding sites and habitat for the vector. However, heavy rainfall may be harmful to mosquito and malaria production. Sometimes too much rain can reduce mosquito populations by washing away developing eggs and larvae, thus reducing the potential for a malaria transmission [21].
Humidity is also of significant effect on the malaria transmission as it facilitates adult mosquito life spans of adequate length. If the average monthly relative humidity is less than 60%, the life of the mosquito is much shortened and therefore malaria transmission is not possible [22].
The burden of malaria
In general, where malaria have hit most, human societies have prospered least[7]. Studies have found that malaria and poverty are highly correlated. These studies have shown that malaria-endemic countries are not only poorer than non-malarious countries, but they also have lower rates of economic growth [7]. Malaria may cause poverty by inhibiting economic growth. There are at least two broad categories of mechanisms through which malaria can impose economic costs well beyond direct medical costs and foregone incomes [23]. These include the negative impact of malaria on trade, tourism or foreign direct investment. The evidence suggests that malaria decreases household savings as families are forced to hire labor to compensate for days lost due to morbidity[24]. In resource-poor countries in Africa, malaria prevention and treatment consume large proportions of health budgets, and since it poses a threat to indigenous populations as well as visitors, it acts as a deterrent to tourism and foreign investment in these countries. Malaria therefore not only affects the health status of African population, but also has significant economic consequences inhibiting economic development[25]. Investors from non-malarious regions tend to avoid malarious regions for fear of contracting the disease[26]. Industries such as tourism are particularly hard hit by the presence of malaria. Investments in all sorts of production may be impeded if the labor force faces a heavy disease burden, or if the burden raises the costs of attracting the needed labor to a malarious region [27].
In Burundi, malaria is a major public health issue with around 2.5 million clinical cases and more than 15.000 deaths each year. For more than a decade, prevalence of malaria in Burundi has been increasing, for example from 548,201 cases in 1991 to 2,8 million cases in 2001[28]. From October 2000 to March 2001, a particularly severe malaria epidemic occurred in the Burundian highlands, with 2.9 million registered cases over a population of 6.7 million and reported attack rates exceeding 200% in some provinces [9]. Between 1,000 to 8,900 probable malaria deaths were reported in three highland provinces, representing between 51% to 78% of the overall mortality [29]. In 2001, Burundi was the world's most affected country[30]. In 2002, malaria accounted for 46% of all consultations in health facilities and 47% of deaths among children under five years of age [31]. This situation of malaria has been aggravated by 15 years of internal war and the increasing of resistance of P. falciparum to first-line (Chloroquine) and second-line (Sulfadoxine Pyrimethamine) drugs[8].
Why is Burundi one of the most affected countries by malaria?
Various factors explain the high prevalence of malaria in Burundi.
15 years of internal conflict. The war and social unrest exacerbated the transmission of malaria by collapsing public health infrastructures (hospitals, clinics,…), public works facilities, destroying countless homes, and displacing large number of people[19]. Some Health workers have been killed or have fled insecure areas.
-Most of Burundi is rural. The promiscuity, poor sanitation and management of wastewater provide suitable breeding pools for mosquitoes. Moreover, most people in rural setting rely on traditional healers as their primary health care.
-Poverty: most of people are not able to afford the consultation and the treatment cost. Few patients seek for medical help in public clinics and hospitals. 81.5% of patients are forced to go into debt or sell property to pay the health costs [32]. In most cases patients buy fewer pills than what is clinically prescribed. People in rural area share the cure. For example a cure of quinine is 21 tablets but it may be shared by 2, 3 or more persons depending on the number of infected in the household.This practice not only led to incomplete treatment, but it also lead to high resistance of the disease to the most affordable drugs[33] . Furthermore, in a country where almost 90 percent of people live on less than two dollars a day, a lot of people are not able to spend 2$ to by a subsidized impregnated bed net [34]. The government initiated a program of distributing free bed nets to the most threatened population. Unfortunately some of the distributed bed nets are resold to the neighboring countries (Tanzania)[35]. Most children and adults are barefoot, this increase the risk of biting by mosquitoes at night. Some children in some rural areas walk bare-chested until the age of five or plus, increasing the likelihood of contact with mosquito.
-Underfunded health sector. The government allocates only 2-4% of its national budget to the health sector [33]. Thus, Burundi's health sector is interdependent to donors' support. Due to years of internal conflict, some donors lost interest in helping Burundi or subjected the aid to a lot of conditionalities.This led to the delay in releasing of the promized or even concelling it.
Poor transportation system in rural area. In most areas, suffering people are curried at tens of kilometers, on a traditional stretcher. This requires the cooperation of neighbors
and it may take some days to gather enough people for this activity. Another problem is that health care workers sometimes have difficulties to distribute drugs or vaccines.
-Malnutrition weakening the immunology of the population: due to 15 years of war, malnutrition has increased among children especially in the displaced people living in precarious conditions.
Changing in agricultural practices including rice paddies, fishing pools and irrigation
in some areas created suitable conditions for malaria transmission by providing breeding pools to the mosquito population.
Insufficient health workers, especially in rural area. The health system suffers from a shortage of qualified personnel with 1 doctor per 34,750 inhabitants and 1 nurse for 3,500 inhabitants. 17.4% of patients do not have access to health care. In addition, some areas lack the infrastructures, facilities, and trained personnel necessary to provide even minimal levels of health services. There is a big disparity between the capital Bujumbura and the remainder of the country as 80% of doctors and more than 50% of nurses are engaged in Bujumbura [32].
Suitable climatic conditions for mosquito development and transmission. Burundi has a tropical climate, with temperature, humidity and rainfall in the range suitable to malaria transmission [3].
A high night temperature. When the indoor temperature is high, many people prefer to spend a large part of the evening outdoor, on open air before going to bed. Some even sleep out of the houses. Further, people don't cover themselves and there is no cooling system in the majority of houses in Burundi. This increases the risk of biting by mosquitoes.
Lack or insufficient indoor lighting. Many houses in rural areas are not enlightened, increasing mosquitoes' activity at night.
Lack of education. 48.4% of the whole population in Burundi are illiterate [36]. This may cause a breach of the rules of hygiene and neglecting of medical prescriptions. Some people prefer to consult the sorcerers instead of health facilities. Some of the freely distributed bed nets are kept packed and are not used [35]. Some of them are even used for wedding decor.
The weakening of public health systems due to malnutrition, associated with famine and massive displacements of the population, failures of control measures and epidemiologic disease surveillance, poor habitat and lack of drinkable water [37].
The prevalence of other diseases such as HIV/AIDS and tuberculosis may have aggravated the situation of malaria by weakening the immune system in the infected population [38].
All these abovementioned factors contribute to the high level of malaria prevalence in Burundi, but climate may have a predominant effect.
Conclusion
Africa (sub-Saharan) is the most affected part by malaria. Many factors explain such situation amongst which are suitable climate and poverty. Malaria is a major threat on Africa in term health and economy. It is still the leading cause of mortality and morbidity in most African countries. Malaria not only affects the health system of the affected countries but also hampers the economic growth in those countries. If Africa is to emerge from its economic slump, a successful control of malaria would be of great asset. Burundi is one of the most affected countries in Africa. The high level of poverty aggravated by long period of internal conflict is the potential fuel of this situation.
References
