The world Health Organization reports that of the top 10 causes of death in low income countries Malaria ranked at position 6, with an alarming crude death rate of 45,000 per 100,000 of the population.1 Malaria is a life-threatening mosquito-borne parasitic infection with protozoa of the genus Plasmodium that is transmitted by the female Anopheles mosquito. Primarily Malarial infections occur in tropical and subtropical regions where temperature, humidity and rainfall are favorable for the Anopheles mosquitoes to thrive. However, malaria can also be found in several temperate areas of the world including the Middle East and Asia. Human malaria is generally transmitted by the bite of one or more of the four species of Plasmodium, namely Plasmodium falciparum, Plasmodium vivax, plasmodium ovale and Plasmodium malariae whose distribution of parasite varies geographically.2 Additionally, a fifth species known as Plasmodium Knowlessi have been added to the list of human malaria as it has been recently prevalent in South East Asia. Malaria can also be transmitted indirectly via-non-mosquito-borne routes such as trans-placentally and infrequently through blood transfusions or organ transplants. This research paper will provide further insight into the Malaria disease, examining vectors and hosts of the disease; the life cycle; epidemiology, treatment and prevention; and the socioeconomic impacts.
VECTORS AND HOSTS
Plasmodium spp typically require a vector and a host in order for the life cycle to be completed. The vector of Plasmodium spp is the female Anopheles mosquito which transmits the parasite and serves as an environment for sexual maturity (definitive host) and the human host or other vertebrae provides an essential environment for the development of the parasite (intermediate host). There are approximately 430 different species of Anopheles mosquitoes; however only about 50 – 60 of them are capable of transmitting malaria. The importance of species of the mosquito varies based on geographical location, as a particular species may be prominent in one part of the world and may be existing but may cause little to no consequence in another part of the world. For example, Anopheles gambiae, is the principal species in sub-Saharan Africa, Anopheles quadrimaculatus is typically found in the east, Anopheles freeborni in the west, and Anopheles pseudopunctipennis along the U.S./Mexico border. Within these locations the female Anopheles takes blood meals from humans and other vertebrae for egg production and will then lay her eggs in a wide range of breeding grounds including fresh or salt water, small streams, irrigated lands, fresh marshes and other places with clean slow-moving water to perpetuate the survival of the species.
Malaria is transmitted to the human host by the introduction of sporozoites via a bite wound during the blood meal of a malaria infected female Anopheles mosquito. The sporozoites initiate the hepatic stage by traveling to the liver cells, where they grow and mature into schizonts. The schizonts rupture sooner or later and release merozoites; however, Plasmodium ovale and Plasmodium vivax have hypnozoites which is a dormant stage of the parasite that can persist in the liver. These hypnozoites can invade the human host’s blood stream weeks or years later and cause a relapse if left untreated. The merozoites initiate the erythrocytic phase of infection by invading human erythrocytes and begin asexual reproduction. The immature ring stage trophozoites mature into schizonts which rupture and release merozoites and can either continue infecting other erythrocytes and reproduce asexually which is responsible for the clinical manifestations or they can differentiate into the sexual erythrocytic stages known as gametocytes. The mosquito stage is initiated when male and female gametocytes (microgametocyte and macrogametocyte respectively) are then ingested by a female Anopheles mosquito during a blood meal and begins sporogony. While in the stomach of the mosquito, the microgamete penetrates the macrogamete which generates zygotes. The zygotes then become ookinetes which can invade the midgut wall of the female Anopheles mosquito and develop into oocyst. The oocysts then grow, rupture and release sporozoites which travels to the salivary glands of the mosquito until the mosquito infects a new host and perpetuates the malaria life cycle.
EPIDEMIOLOGY, DISEASE, TREATMENT AND PREVENTION
Malaria affects almost half of the world’s population and remains a serious global health problem occurring in the world with the highest burden of mortality (93%) and morbidity (92%) occurring in sub-Saharan Africa. (immunity article) Despite the progress and advances in the approaches to prevent malaria, there is still an alarming number of people infected most occurring in children under 5 and pregnant women. According to WHO, the most recent reports state that there were 219 million cases of malaria in 90 countries compared to the 214 million cases in 2015. Of the 219 million, approximately 435,000 lives were claimed in 2017.
Malaria is an acute febrile illness that can be classed as severe or uncomplicated. Uncomplicated malaria involves a cold stage, a hot stage and a sweating stage that occurs at a consistent rate; however, the duration of schizogony depends on the species of plasmodium the patient is infected with. Generally, in uncomplicated malaria an infected person may experience symptoms such as fever, chills, sweats, headaches, nausea and vomiting, body aches and general malaise. Severe malaria, on the other hand, is a medical emergency and occurs when the patient is experiencing complications such as significant abnormalities in their blood metabolism and vital organ failure. Symptoms of severe malaria may include but are not limited to Cerebral malaria which is characterized by abnormal behavior, impairment of consciousness, seizures, coma, or other neurologic abnormalities. It can also cause severe anemia and hemoglobinuria due to red blood cell hemolysis, as well as hyperparasitemia. Thus, when a patient is suspected to have severe malaria treatment should be administered promptly and aggressively. Plasmodium falciparum is the most potent species and is the main contributor of severe malaria.
Malaria if treated promptly can be cured. Previously the drug of choice to treat malaria was chlornquine; however, due to the worldwide spread of drug resistance Plasmodium falciparum is no longer treatable by this drug. As a result, the preferred treatments for severe malaria are currently cinchona alkaloids such as quinidine and artemisinin derivatives such as artesunate, artemether, and artemotil. Additionally, blood transfusions are recommended to help compensate for the red blood cell destruction in all cases of malarial infection if the patient’s hemoglobin is less than 4g/dL, or when parasitemia is more than 20%.
According to the Center for Disease Control, the best way to prevent the spread of malaria is to avoid mosquito bites by sleeping in insecticide treated mosquito sleeping nets, indoor residual spraying with DEET or picaridin based repellents, preventative treatment for pregnant women such as administration of sulfadoxine-pyrimethamine and properly managing current cases.4 To further combat this disease researchers have been trying to find antigens that could induce protective immunity against malaria for several years but have been unsuccessful, thus, the “holy grail” for the control of malaria is the Malaria vaccine that targets three phases of the malarial life cycle. The vaccines are directed against either the pre-erythrocytic stages of the parasite by blocking development or invasion of sporozoites, the mosquito’s sexual stages by inhibiting parasitic development or the erythrocytic stages by reducing the patient’s parasitic burden.
Though rigorous efforts are being made to help control the spread of malaria in Sub-Saharan Africa, the distribution of the disease is disproportionately high, and it remains one of the deadliest diseases and the greatest killers of children. Africa is struggling to win the fight against malaria because most Sub-Saharan infections are caused by Plasmodium falciparum, which is the most pathogenic and drug resistant species to the cheapest and most widely used drug in Africa. Additionally, Africa has environmental conditions ideal for the thriving of the Anopheles mosquito, as a result they tend to have the most aggressive species of mosquitoes resulting in an increase in transmission rates. In addition to the social and public health problems, malaria is also an economic issue as it causes an estimated loss of $12 million yearly in Africa due to the increase in cost of healthcare, loss of ability to work and to the negative effects on tourism. Malaria also poses an unbearable economic burden on households as they are faced with the purchasing of insecticide coated sleeping nets, transportation to healthcare, the cost of antimalarial drugs and the cost of funeral arrangements.
Malaria is a life-threatening mosquito-borne parasitic infection with protozoa of the genus Plasmodium transmitted by the female Anopheles mosquito. Infections generally occur where climates are temperate and favorable for the mosquito. Malaria affects almost half of the world’s population and remains a serious global health problem mostly occurring in children under 5 and pregnant women. Malaria is an acute febrile illness that can be classed as severe or uncomplicated based upon the species infected with and is usually curable with treatment. The best way to prevent malaria is by sleeping in insecticide coated sleeping nets, indoor residual spraying and antimalarial drugs. Rigorous efforts made to combat malaria however many families still suffer the economic burden of living where malaria is endemic.
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