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''Plasmodium falciparum'' ring-forms and gametocytes in human blood
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Malaria
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is a
Vector -borne
Infectious Disease caused by
Protozoan Parasite s. It is widespread in
Tropical and subtropical regions, including parts of the
Americas ,
Asia , and
Africa . Each year, it causes disease in approximately 650 million people and kills between one and three million, most of them young children in
Sub-Saharan Africa . Malaria is commonly-associated with poverty, but is also a cause of poverty and a major hindrance to
Economic Development .
Malaria is one of the most common infectious diseases and an enormous public-health problem. The disease is caused by
Protozoan Parasite s of the
Genus ''
Plasmodium ''. The most serious forms of the disease are caused by ''
Plasmodium Falciparum '' and ''
Plasmodium Vivax '', but other related species (''
Plasmodium Ovale '', ''
Plasmodium Malariae '', and sometimes ''
Plasmodium Knowlesi '') can also infect humans. This group of human-pathogenic ''Plasmodium'' species is usually referred to as ''malaria parasites''.
Malaria parasites are transmitted by female ''
Anopheles ''
Mosquito es. The parasites multiply within
Red Blood Cell s, causing symptoms that include symptoms of
Anemia (light headedness, shortness of breath, tachycardia etc.), as well as other general symptoms such as
Fever ,
Chills ,
Nausea ,
Flu-like Illness , and in severe cases,
Coma and death. Malaria transmission can be reduced by preventing mosquito bites with
Mosquito Net s and
Insect Repellent s, or by mosquito control by spraying
Insecticide s inside houses and draining standing water where mosquitoes lay their eggs.
No
Vaccine is currently available for malaria; preventative drugs must be taken continuously to reduce the risk of infection. These
Prophylactic drug treatments are often too expensive for most people living in endemic areas. Most adults from endemic areas have a degree of long-term recurrent infection and also of partial resistance; the resistance reduces with time and such adults may become susceptible to severe malaria if they have spent a significant amount of time in non-endemic areas. They are strongly recommended to take full precautions if they return to an endemic area. Malaria infections are treated through the use of
Antimalarial Drug s, such as
Quinine or
Artemisinin derivatives, although
Drug Resistance is increasingly common.
Malaria has infected humans for over 50,000 years, and may have been a human "; and the disease was formerly called or '''marsh fever''' due to its association with swamps.
Scientific studies on malaria made their first significant advance in 1880, when a French army doctor working in
Algeria named
Charles Louis Alphonse Laveran observed parasites inside the
Red Blood Cell s of people suffering from malaria. He therefore proposed that malaria was caused by this
Protozoa n, the first time protozoa were identified as causing disease.
4 ] Nobel foundation. Accessed 25 Oct 2006 For this and later discoveries, he was awarded the 1907
Nobel Prize For Physiology Or Medicine . The protozoan was called ''Plasmodium'' by the Italian scientists
Ettore Marchiafava and
Angelo Celli .
5 A year later,
Carlos Finlay , a Cuban doctor treating patients with
Yellow Fever in
Havana , first suggested that mosquitoes were transmitting disease to and from humans. However, it was Britain's
Sir Ronald Ross working in
India who finally proved in 1898 that malaria is transmitted by mosquitoes. He did this by showing that certain mosquito species transmit malaria to birds and isolating malaria parasites from the salivary glands of mosquitoes that had fed on infected birds.
6 For this work Ross received the 1902 Nobel Prize in Medicine. After resigning from the Indian Medical Service, Ross worked at the newly-established
Liverpool School Of Tropical Medicine and directed malaria-control efforts in
Egypt ,
Panama ,
Greece and
Mauritius .
7 The findings of Finlay and Ross were later confirmed by a medical board headed by
Walter Reed in 1900, and its recommendations implemented by
William C. Gorgas in
The Health Measures Undertaken during construction of the
Panama Canal . This public-health work saved the lives of thousands of workers and helped develop the methods used in future public-health campaigns against this disease.
The first effective treatment for malaria was the bark of
Cinchona Tree , which contains
Quinine . This tree grows on the slopes of the
Andes , mainly in
Peru . This natural product was used by the inhabitants of
Peru to control malaria, and the
Jesuit s introduced this practice to Europe during the 1640s where it was rapidly accepted.
8 However, it was not until
1820 that the active ingredient quinine was extracted from the bark, isolated and named by the French chemists
Pierre Joseph Pelletier and
Jean Bienaime Caventou .
9
In the early twentieth century, before
Antibiotics , patients with
Syphilis were intentionally
Infected with malaria to create a
Fever , following the work of
Julius Wagner-Jauregg . By accurately controlling the fever with
Quinine , the effects of both syphilis and malaria could be minimized. Although some patients died from malaria, this was preferable than the almost-certain death from syphilis.
10
Although the blood stage and mosquito stages of the malaria life cycle were established in the 19th and early 20th centuries, it was not until the 1980s that the latent liver form of the parasite was observed.
1112 The discovery of this latent form of the parasite finally explained why people could appear to be cured of malaria but still relapse years after the parasite had disappeared from their bloodstreams.
in the 21st Century (coloured blue).
13]]
Malaria causes about 400–900 million cases of fever and approximately one to three million deaths annually
14 — this represents at least one death every 30 seconds. The vast majority of cases occur in children under the age of 5 years;
15 pregnant women are also especially vulnerable. Despite efforts to reduce transmission and increase treatment, there has been little change in which areas are at risk of this disease since 1992.
16 Indeed, if the prevalence of malaria stays on its present upwards course, the death rate could double in the next twenty years. Precise statistics are unknown because many cases occur in rural areas where people do not have access to hospitals or the means to afford health care. Consequently, the majority of cases are undocumented.
Although co-infection with HIV and malaria does cause increased mortality, this is less of a problem than with HIV/
Tuberculosis co-infection, due to the two diseases usually attacking different age-ranges, with malaria being most common in the young and active tuberculosis most common in the old.
17 Although HIV/malaria co-infection produces less severe symptoms than the interaction between HIV and TB, HIV and malaria do contribute to each other's spread. This effect comes from malaria increasing
Viral Load and HIV infection increasing a person's susceptibility to malaria infection.
18
Malaria is presently endemic in a broad band around the equator, in areas of the
Americas , many parts of
Asia , and much of
Africa ; however, it is in sub-Saharan Africa where 85– 90% of malaria fatalities occur.
19 The geographic distribution of malaria within large regions is complex, and malarial and malaria-free areas are often found close to each other.
20 In drier areas, outbreaks of malaria can be predicted with reasonable accuracy by mapping rainfall.
21 Malaria is more common in rural areas than in cities; this is in contrast to
Dengue Fever where urban areas present the greater risk.
22 For example, the cities of the
Vietnam ,
Laos and
Cambodia are essentially malaria-free, but the disease is present in many rural regions.
23 By contrast, in Africa malaria is present in both rural and urban areas, though the risk is lower in the larger cities.
24 The global
Endemic levels of malaria have not been mapped since the 1960s, however, the
Wellcome Trust , UK, has funded the
Malaria Atlas Project 25 to rectify this, providing a more contemporary and robust means with which to assess current and future malaria
Disease Burden .
Malaria is not just a disease commonly associated with poverty, but is also a cause of poverty and a major hindrance to
Economic Development . The disease has been associated with major negative economic effects on regions where it is widespread. A comparison of average per capita GDP in 1995, adjusted to give parity of purchasing power, between malarious and non-malarious countries demonstrates a fivefold difference (US$1,526 versus US$8,268). Moreover, in countries where malaria is common, average per capita GDP has risen (between 1965 and 1990) only 0.4% per year, compared to 2.4% per year in other countries.
26 However, correlation does not imply causation, and the prevalence is at least partly because that these regions do not have the financial capacities to prevent malaria. In its entirety, the economic impact of malaria has been estimated to cost Africa US$12 billion every year. The economic impact includes costs of health care, working days lost due to sickness, days lost in education, decreased productivity due to brain damage from cerebral malaria, and loss of investment and tourism. In some countries with a heavy malaria burden, the disease may account for as much as 40% of public health expenditure, 30-50% of inpatient admissions, and up to 50% of outpatient visits.
27
Symptoms of malaria include , children with malaria frequently exhibit
Abnormal Posturing , a sign indicating severe brain damage.
28 Malaria has been found to cause cognitive impairments, especially in children. It causes widespread
Anemia during a period of rapid brain development and also direct brain damage. This neurologic damage results from cerebral malaria to which children are more vulnerable.Boivin, M.J., "
Effects of early cerebral malaria on cognitive ability in Senegalese children ," ''Journal of Developmental and Behavioral Pediatrics'' 23, no. 5 (October 2002): 353–64. Holding, P.A. and Snow, R.W., "
Impact of Plasmodium falciparum malaria on performance and learning: review of the evidence ," ''American Journal of Tropical Medicine and Hygiene'' 64, suppl. nos. 1–2 (January–February 2001): 68–75.
Severe malaria is almost exclusively caused by ''P. falciparum'' infection and usually arises 6-14 days after infection.
29 Consequences of severe malaria include
Coma and death if untreated—young children and pregnant women are especially vulnerable.
Splenomegaly (enlarged spleen), severe
Headache , cerebral
Ischemia ,
Hepatomegaly (enlarged liver),
Hypoglycemia , and hemoglobinuria with
Renal Failure may occur. Renal failure may cause
Blackwater Fever , where hemoglobin from lysed red blood cells leaks into the urine. Severe malaria can progress extremely rapidly and cause death within hours or days. In the most severe cases of the disease fatality rates can exceed 20%, even with intensive care and treatment.
30 In endemic areas, treatment is often less satisfactory and the overall fatality rate for all cases of malaria can be as high as one in ten.
31 Over the longer term, developmental impairments have been documented in children who have suffered episodes of severe malaria.
32
Chronic malaria is seen in both ''P. vivax'' and ''P. ovale'', but not in ''P. falciparum''. Here, the disease can relapse months or years after exposure, due to the presence of latent parasites in the liver. Describing a case of malaria as cured by observing the disappearance of parasites from the bloodstream can therefore be deceptive. The longest incubation period reported for a ''P. vivax'' infection is 30 years. Approximately one in five of ''P. vivax'' malaria cases in
Temperate areas involve overwintering by hypnozoites (i.e., relapses begin the year after the mosquito bite).
33
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Malaria is caused by , which evolved in its absence and lack any resistance to it.
37
The parasite's primary (definitive) hosts and transmission
Vector s are female
Mosquito es of the ''
Anopheles '' genus. Young mosquitoes first ingest the malaria parasite by feeding on an infected human carrier and the infected ''
Anopheles '' mosquitoes carry ''Plasmodium''
Sporozoite s in their
Salivary Gland s. A mosquito becomes infected when it takes a blood meal from an infected human. Once ingested, the parasite
Gametocytes taken up in the blood will further differentiate into male or female
Gametes and then fuse in the mosquito gut. This produces an
Ookinete that penetrates the gut lining and produces an
Oocyst in the gut wall. When the oocyst ruptures, it releases
Sporozoites that migrate through the mosquito's body to the salivary glands, where they are then ready to infect a new human host. This type of transmission is occasionally referred to as anterior station transfer.
38 The sporozoites are injected into the skin, alongside saliva, when the mosquito takes a subsequent blood meal.
Only female mosquitoes feed on blood, thus males do not transmit the disease. The females of the ''
Anopheles '' genus of mosquito prefer to feed at night. They usually start searching for a meal at dusk, and will continue throughout the night until taking a meal. Malaria parasites can also be transmitted by
Blood Transfusion s, although this is rare.
39
