Malaria is a mosquito-borne infectious disease of humans and other animals caused by eukaryotic protists (a type of microorganism) of the genus Plasmodium. The protists first infect the liver, then act as parasites within red blood cells, causing symptoms that typically include fever and headache, in severe cases progressing to coma or death. The disease is widespread in tropical and subtropical regions in a broad band around the equator, including much of Sub-Saharan Africa, Asia, and the Americas.Five species of Plasmodium can infect and be transmitted by humans. Severe disease is largely caused by P. falciparum while the disease caused by P. vivax, P. ovale, and P. malariae is generally a milder form that is rarely fatal. The zoonotic species P. knowlesi, prevalent in Southeast Asia, causes malaria in macaques but can also cause severe infections in humans. Malaria is prevalent in tropical regions because the significant amounts of rainfall, consistently high temperatures and high humidity, along with stagnant waters in which mosquito larvae readily mature, provide them with the environment they need for continuous breeding. Disease transmission can be reduced by preventing mosquito bites by distribution of mosquito nets and insect repellents, or with mosquito-control measures such as spraying insecticides and draining standing water.The World Health Organization has estimated that in 2010, there were 216 million cases of malaria. Around 655,000 people died from the disease, most of whom were children under the age of five.CAUSES,INCIDENCE,AND RISKS
Malaria is caused by a parasite that is passed from one human to another by the bite of infected Anopheles mosquitoes. After infection, the parasites (called sporozoites) travel through the bloodstream to the liver, where they mature and release another form, the merozoites. The parasites enter the bloodstream and infect red blood cells.
The parasites multiply inside the red blood cells, which then break open within 48 to 72 hours, infecting more red blood cells. The first symptoms usually occur 10 days to 4 weeks after infection, though they can appear as early as 8 days or as long as a year after infection. The symptoms occur in cycles of 48 to 72 hours.
Most symptoms are caused by:
-The release of merozoites into the bloodstream
-Anemia resulting from the destruction of the red blood cells
-Large amounts of free hemoglobin being released into circulation after red blood cells break open
-Malaria can also be transmitted from a mother to her unborn baby (congenitally) and by blood transfusions. -Malaria can be carried by mosquitoes in temperate climates, but the parasite disappears over the winter.
The disease is a major health problem in much of the tropics and subtropics. The CDC estimates that there are 300-500 million cases of malaria each year, and more than 1 million people die from it. It presents a major disease hazard for travelers to warm climates
There are four types of common malaria parasites. Recently, a fifth type, Plasmodium knowlesi, has been causing malaria in Malaysia and areas of southeast Asia. Another type, falciparum malaria, affects more red blood cells than the other types and is much more serious. It can be fatal within a few hours of the first symptoms.
SIGNS AND SYMPTOMS
The signs and symptoms of malaria typically begin 8–25 days following infection.However, symptoms may occur later in those who have taken antimalarial medications as prevention.The presentation may include fever, shivering, arthralgia (joint pain), vomiting, hemolytic anemia, jaundice, hemoglobinuria, retinal damage, and convulsions. Approximately 30% of people however will no longer have a fever upon presenting to a health care facility.
The classic symptom of malaria is cyclical occurrence of sudden coldness followed by rigor and then fever and sweating lasting about two hours or more, occurring every two days in P. vivax and P. ovale infections, and every three days for P. malariae. P. falciparum infection can cause recurrent fever every 36–48 hours or a less pronounced and almost continuous fever.For reasons that are poorly understood, but that may be related to high intracranial pressure, children with malaria frequently exhibit abnormal posturing, a sign indicating severe brain damage.Cerebral malaria is associated with retinal whitening, which may be a useful clinical sign in distinguishing malaria from other causes of fever.
Severe malaria is usually caused by P. falciparum, and typically arises 6–14 days after infection.Non-falciparum species have however been found to be the cause of ~14% of cases of severe malaria in some groups.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 is a feature of blackwater fever, where hemoglobin from lysed red blood cells leaks into the urine.
Recurrent malaria
Malaria recurs after treatment for three reasons. Recrudescence occurs when parasites are not cleared by treatment, whereas reinfection indicates complete clearance with new infection established from a separate infective mosquito bite; both can occur with any malaria parasite species. Relapse is specific to P. vivax and P. ovale and involves re-emergence of blood-stage parasites from latent parasites (hypnozoites) 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, with relapses beginning the year after the mosquito bite.
Malarial hepatopathy
Hepatic dysfunction as a result of malaria is rare and is usually a result of a coexisting liver condition such as viral hepatitis and chronic liver disease. Hepatitis, which is characterized by inflammation of the liver, is not actually present in what is called malarial hepatitis; the term as used here invokes the reduced liver function associated with severe malaria. While traditionally considered a rare occurrence, malarial hepatopathy has seen an increase in malaria endemic areas, particularly in Southeast Asia and India. Liver compromise in people with malaria correlates with a greater likelihood of complications and death.
SIGNS AND SYMPTOMS
During a physical examination, the doctor may find an enlarged liver or enlarged spleen. Malaria blood smears taken at 6 to 12 hour intervals confirm the diagnosis.A complete blood count (CBC) will identify anemia if it is present.
PREVENTION
Anopheles albimanus mosquito feeding on a human arm. This mosquito is a vector of malaria and mosquito control is an effective way of reducing the incidence of malaria.
Methods used to prevent malaria include medications, mosquito eradication and the prevention of bites. The presence of malaria in an area requires a combination of high human population density, high mosquito population density and high rates of transmission from humans to mosquitoes and from mosquitoes to humans. If any of these is lowered sufficiently, the parasite will eventually disappear from that area, as happened in North America, Europe and much of the Middle East. However, unless the parasite is eliminated from the whole world, it could become re-established if conditions revert to a combination that favours the parasite's reproduction. Many countries are seeing an increasing number of imported malaria cases owing to extensive travel and migration.
Many researchers argue that prevention of malaria may be more cost-effective than treatment of the disease in the long run, but the capital costs required are out of reach of many of the world's poorest people. There is a wide disparity in the costs of control (i.e. maintenance of low endemicity) and elimination programs between countries. For example, in China—whose government in 2010 announced a strategy to pursue malaria elimination in the Chinese provinces—the required investment is a small proportion of public expenditure on health. In contrast, a similar program in Tanzania would cost an estimated one-fifth of the public health budget.
Several drugs, most of which are used for treatment of malaria, can be taken preventively. Chloroquine may be used where the parasite is still sensitive. However, due to resistance one of three medications—mefloquine (Lariam), doxycycline (available generically), or the combination of atovaquone and proguanil hydrochloride (Malarone)—is frequently needed. Doxycycline and the atovaquone and proguanil combination are the best tolerated; mefloquine is associated with higher rates of neurological and psychiatric symptoms.
The prophylactic effect does not begin immediately upon starting the drugs, so people temporarily visiting malaria-endemic areas usually begin taking the drugs one to two weeks before arriving and should continue taking them for four weeks after leaving (with the exception of atovaquone proguanil that only needs to be started two days prior and continued for seven days afterwards). Generally, these drugs are taken daily or weekly, at a lower dose than is used for treatment of a person who contracts the disease. Use of prophylactic drugs is seldom practical for full-time residents of malaria-endemic areas, and their use is usually restricted to short-term visitors and travelers to malarial regions. This is due to the cost of purchasing the drugs, negative adverse effects from long-term use, and because some effective anti-malarial drugs are difficult to obtain outside of wealthy nations. The use of prophylactic drugs where malaria-bearing mosquitoes are present may encourage the development of partial immunity.
Man spraying kerosene oil to protect against mosquitoes carrying malaria, Panama Canal Zone 1912
Efforts to eradicate malaria by eliminating mosquitoes have been successful in some areas. Malaria was once common in the United States and southern Europe, but vector control programs, in conjunction with the monitoring and treatment of infected humans, eliminated it from those regions. In some areas, the draining of wetland breeding grounds and better sanitation were adequate.
Indoor residual spraying (IRS) is the practice of spraying insecticides on the interior walls of homes in malaria-affected areas. After feeding, many mosquito species rest on a nearby surface while digesting the bloodmeal, so if the walls of dwellings have been coated with insecticides, the resting mosquitos will be killed before they can bite another victim and transfer the malaria parasite.
The first pesticide used for IRS was DDT.[41] Although it was initially used exclusively to combat malaria, its use quickly spread to agriculture. In time, pest control, rather than disease control, came to dominate DDT use, and this large-scale agricultural use led to the evolution of resistant mosquitoes in many regions. The DDT resistance shown by Anopheles mosquitoes can be compared to antibiotic resistance shown by bacteria. The overuse of antibacterial soaps and antibiotics led to antibiotic resistance in bacteria, similar to how overspraying of DDT on crops led to DDT resistance in Anopheles mosquitoes. During the 1960s, awareness of the negative consequences of its indiscriminate use increased, ultimately leading to bans on agricultural applications of DDT in many countries in the 1970s. Since the use of DDT has been limited or banned for agricultural use for some time, DDT may now be more effective as a method of disease-control.
Mosquito nets create a protective barrier against malaria-carrying mosquitoes that bite at night.
Mosquito nets help keep mosquitoes away from people and significantly reduce infection rates and transmission of malaria. The nets are not a perfect barrier and they are often treated with an insecticide designed to kill the mosquito before it has time to search for a way past the net. Insecticide-treated nets (ITNs) are estimated to be twice as effective as untreated nets and offer greater than 70% protection compared with no net. Although ITNs are proven to be very effective against malaria, only about 13% of households in sub-Saharan countries own them.Since the Anopheles mosquitoes feed at night, the preferred method is to hang a large "bed net" above the center of a bed to drape over it completely.Other methods
Community participation and health education strategies promoting awareness of malaria and the importance of control measures have been successfully used to reduce the incidence of malaria in some areas of the developing world. Recognizing the disease in the early stages can stop the disease from becoming fatal. Education can also inform people to cover over areas of stagnant, still water, such as water tanks that are ideal breeding grounds for the parasite and mosquito, thus cutting down the risk of the transmission between people. This is generally used in urban areas where there are large centers of population in a confined space and transmission would be most likely in these areas.
Other interventions for the control of malaria include mass drug administrations and intermittent preventive therapy.
TREATMENT
When properly treated, people with malaria can usually expect a complete recovery. The treatment depends on the severity of the disease; whether people can take oral drugs or must be admitted depends on the assessment and the experience of the clinician.
Uncomplicated malaria
Uncomplicated malaria may be treated with oral medications. The most effective strategy for P. falciparum infection is the use of artemisinins in combination with other antimalarials (known as artemisinin-combination therapy).This is done to reduce the risk of resistance against artemisinin. These additional antimalarials include amodiaquine, lumefantrine, mefloquine or sulfadoxine/pyrimethamine.Another recommended combination is dihydroartemisinin and piperaquine. Recently, malaria with partial resistance to artemisins has occurred in Southeast Asia
Severe malaria
Severe malaria requires the parenteral administration of antimalarial drugs. Until the mid-2000s the most used treatment for severe malaria was quinine, but artesunate has been shown to be superior to quinine in both children and adults.Treatment of severe malaria also involves supportive measures. Infection with P. vivax, P. ovale or P. malariae is usually treated on an outpatient basis (while a person is at home). Treatment of P. vivax requires both treatment of blood stages (with chloroquine or ACT) as well as clearance of liver forms with primaquine
PROGNOSIS
Disability-adjusted life year for malaria per 100,000 inhabitants in 2004.
no data
<10
10–100
100–500
500–1000
1000–1500
1500–2000
2000–2500
2500–2750
2750–3000
3000–3250
3250–3500
≥3500
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.Over the longer term, developmental impairments have been documented in children who have suffered episodes of severe malaria. 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.
