Malaria
medical conditions

Malaria

Explore the available health information, treatment context, and integrative evidence for Malaria.

Background
  • Malaria is a disease that can be transmitted to people of all ages. Malaria is caused by parasites of the genus Plasmodium that are spread from one individual to another through the bites of infected mosquitoes.
  • The common first symptoms include fever, headache, chills, and vomiting. These symptoms appear 10-15 days after an individual is infected. If not treated promptly with effective medicines, malaria can cause severe illness that is often fatal.
  • Malaria transmission differs in intensity and regularity depending on local factors such as rainfall patterns, proximity of mosquito breeding sites, and mosquito species. The Anopheles mosquito, or more commonly referred to as the "common malaria" mosquito, transmits the disease of malaria. Some regions are endemic areas and have a fairly constant number of cases throughout the year. Other areas have "malaria" seasons, usually coinciding with the rainy season. The rainy season provides more places for standing water where the mosquito can lay eggs.
  • Large and devastating epidemics can occur in areas where people have had little contact with the malaria parasite, and therefore have little or no immunity. These epidemics can be triggered by weather conditions and further aggravated by natural disasters.
  • About 40% of the world's population, largely living in undeveloped countries, is at risk of malaria. Most cases and deaths are in sub-Saharan Africa where one in every five (20%) childhood deaths is due to the effects of the disease, such as dehydration. Every 30 seconds, a child in Africa dies from malaria. However, Asia, Latin America, the Middle East, and parts of Europe are also affected. Of these 2.5 billion people at risk, more than 500 million become severely ill with malaria every year and more than one million die from the effects of the disease.
  • Most American cases of malaria develop in travelers who have recently returned from parts of the world where malaria is widespread. If an individual is traveling to malaria-endemic places, it is recommended by healthcare professionals to take precautions before, during, and after the trip. Bednets, insecticides and antimalarial drugs are available for both the prevention and treatment of malaria.

Risk Factors and Causes
  • Plasmodium is a genus of parasitic protozoa that causes malaria. The four species known to cause malaria in humans are:
  • Plasmodium falciparum
    : P. falcatum, predominant in Africa, produces the most severe symptoms and is responsible for most malaria deaths.
  • Plasmodium vivax
    : P. vivax, found mostly in tropical areas of Asia, produces less severe symptoms but can remain in the liver and cause relapses for up to three years.
  • Plasmodium malariae
    : P. malariae, found in Africa, can cause typical malaria symptoms, but on rare occasions it can remain in the bloodstream for years without producing symptoms. In these cases, is it possible to pass on the parasite to a mosquito or to another person through a blood transfusion.
  • Plasmodium ovale
    : P. ovale is found mostly in West Africa. Although infections with P. ovale are rare, relapses may occur.
  • The process of transmission:
    In nature, malaria parasites spread by successively infecting two types of hosts: humans and female Anopheles mosquitoes. In humans, the parasites grow and multiply first in the liver cells and then in the red blood cells. Successive broods of parasites grow inside the red blod cells and destroy them, releasing daughter parasites ("merozoites") that continue the cycle by invading other red blood cells.
  • The blood stage parasites are those that cause the symptoms of malaria. When certain forms of blood stage parasites ("gametocytes") are picked up by a female Anopheles mosquito during a blood meal, they start another, different cycle of growth and multiplication in the mosquito. Only the female mosquitoes are transmitters because they can penetrate the skin of a person; the male mosquito proboscis is not able to pierce the skin.
  • After 10-18 days, the parasites are found (as "sporozoites") in the mosquito's salivary glands. When the Anopheles mosquito takes a blood meal on another human, the sporozoites are injected with the mosquito's saliva and start another human infection when they parasitize the liver cells.
  • The mosquito carries the disease from one human to another (acting as a "vector"). Differently from the human host, the mosquito vector does not suffer from the presence of the parasites.
  • Typically, signs and symptoms begin 10 days to four weeks after the initial mosquito bite, although they can appear as early as eight days or as late as one year later. Symptoms include: asymptomatic infections (no apparent illness), fever, chills, sweating, headaches, muscle pains, cerebral malaria, anemia and kidney failure and may result in death. The severity of the symptoms depends on several factors, such as the species (type) of infecting parasite and the human's acquired immunity and genetic background.
  • In many cases, medication or the immune system eventually helps stop the infection. But in other cases, particularly in children whose immune systems may not yet have adapted to the parasite, complications of the infection may lead to death. In addition, P. falciparum is capable of invading a much greater number of blood cells than are the other types of Plasmodium, and the infection can be fatal within a few hours of initial red blood cell rupture.
  • Other means of transmission:
    A pregnant woman can transmit the infection to her unborn baby. Malaria may be transmitted through blood transfusions. In the United States, steps have been taken to prevent this type of transmission. Individuals who have visited a malaria-endemic area are prohibited from donating blood for a year after returning from the malaria-infected area, or three years if they have been a resident of the malaria-infected area or have been treated for malaria. Malaria can be detected in the blood of an infected individual through blood testing.
  • A main risk factor for contracting malaria is living in a region of the world prone to malaria, such as large areas of Central and South America, sub-Saharan Africa, the Indian subcontinent, Southeast Asia, the Middle East, and Oceania.
  • Individuals who have little or no immunity to malaria are most at risk for serious illness. Residents of a malaria region may acquire some immunity to the disease during their lifetime, but young children and infants who have yet to acquire any immunity are at risk, as are travelers coming from areas with no malaria.
  • A pregnant woman is more vulnerable than other people are to P. falciparum malaria, as is her unborn child.
  • Poverty, lack of knowledge, and little or no access to healthcare also contribute to malaria deaths worldwide.
  • It is also possible to lose immunity if the individual is no longer frequently exposed to the parasite. Even if the individual has previously lived in a malaria-infected region, it is recommended by healthcare professionals to take antimalarial precautions (such as antimalarial drugs) when returning to such an area after an extended period away.
Signs and Symptoms
  • Malaria can occur while antimalarial drugs are being taken due to drug resistance (see "Treatment").
  • Symptoms of malaria usually appear about 10-14 days after being bittenby an infected mosquito. Symptoms include: sudden, violent chills; intermittent fever; sweating; exhaustion and fatigue; headaches; seizures; and delirium.
  • Plasmodium falciparum infections normally take 7-14 days to show symptoms while Plasmodium vivax and Plasmodium ovale normally take 8-14 days (but in some cases can survive for some months in the human horst). Plasmodium malariae infections take 7-30 days.
  • Fever in the first week of travel in a malaria-risk area is unlikely to be malaria; however, any traveler feeling ill should seek immediate medical care.
Diagnosis
  • After noting symptoms and travel history, a doctor will likely obtain a sample (smear) of the individual's blood for observation under a microscope. Two blood samples, taken at six- and 12-hour intervals, can usually confirm the presence of the malaria parasite and its type. It is possible to be infected by more than one Plasmodium at the same time.
  • Enzyme-linked immunosorbent assay (ELISA): An enzyme-linked immunosorbent assay (ELISA) test is a blood test that looks for an antigen that is specific to malaria parasites. An antigen is any substance, such as a virus, bacterium, toxin, or foreign protein, which triggers an immune system response in the body.
Complications
  • Most complications of malaria are associated with infection by Plasmodium falciparum. The extensive destruction of red blood cells that occurs during malaria infection may result in severe anemia. In addition, if parasite-filled blood cells block small blood vessels to the brain (cerebral malaria), swelling of the brain or brain damage may occur. Other complications may include: breathing problems, at times severe in the form of accumulated fluid in the lungs (pulmonary edema); dehydration; liver failure; kidney failure; and rupture of the spleen.
  • If untreated, P. falciparum malaria can be fatal within a matter of hours after symptoms appear.
Treatment
  • Because malaria infection often initially appears to be a flu-like illness or some other viral disease, individuals should be wary if they develop an illness with fever while living in a malaria-endemic area or within 12 months after traveling to a high-risk malaria region. It is recommended by healthcare professionals to see a doctor as soon as possible and inform the doctor about the countries that were visited. Left untreated, a malaria infection can cause serious, potentially life-threatening health problems.
  • Malaria infection, particularly with Plasmodium falciparum, requires prompt evaluation and treatment. In most cases, doctors can treat malaria effectively with anti-malarial drugs.
  • The Centers for Disease Control and Prevention (CDC) recommend that treatment be guided by three main factors: the infecting Plasmodium species, the clinical status of the patient, and the drug susceptibility of the infecting parasites as determined by the geographic area where the infection was acquired.
  • According to the CDC's Web site, determination of the infecting Plasmodium species for treatment purposes is important for three main reasons: P. falciparum infections can cause rapidly progressive severe illness or death while the non-falciparum (P. vivax, P. ovale,
    or P. malariae) species rarely cause severe manifestations; P. vivax and P. ovale infections require treatment for the hypnozoite forms that remain dormant in the liver and can cause a relapsing infection; and P. falciparum and P. vivax species have different drug resistance patterns in differing geographic regions.
  • The second factor affecting treatment, the clinical status of the patient, is used to categorize patients as having either uncomplicated or severe malaria. Patients diagnosed with uncomplicated malaria can be effectively treated with oral antimalarials. However, patients who have one or more of the following clinical criteria - impaired consciousness/coma, severe normocytic anemia, renal failure, pulmonary edema, acute respiratory distress syndrome, circulatory shock, disseminated intravascular coagulation, spontaneous bleeding, acidosis, hemoglobinuria, jaundice, repeated generalized convulsions, and/or parasitemia of greater than five percent - are considered to have manifestations of more severe disease and should be treated aggressively with parenteral antimalarial therapy.
  • And lastly, knowledge of the geographic area where the infection was acquired provides information on the likelihood of drug resistance of the infecting parasite enabling the treating clinician to choose an appropriate drug or drug combination and treatment course. If the diagnosis of malaria is suspected and cannot be confirmed, or if the diagnosis of malaria is confirmed but species determination is not possible, the CDC recommends that antimalarial treatment effective against P. falciparum be initiated immediately.
  • In the Untied States, malaria is a nationally notifiable disease and all cases should be reported to the individual's state health department. CDC clinicians are on-call 24 hours to provide advice to clinicians on the diagnosis and treatment of malaria and can be reached through the Malaria Hotline.
  • Another class of antimalarial drugs, often prescribed in Asia and now in other parts of the world, is derived from artemisinin, a sweet wormwood (Artemesia annua) extract. Primaquine may be given to fight the dormant liver form of the parasite and prevent relapses. However, the CDC has warned against taking primaquine if the individuals is pregnant or has an enzyme deficiency called G6PD (glucose-6-phosphate dehydrogenase) deficiency. Doctors will not use primaquine until the individual has passed a screening test for G6PD deficiency.
  • Side effects of antimalarial drugs include nausea, vomiting, and stomach upset. The antimalarial drug mefloquine (Lariam®) has received attention because of reports that it causes panic attacks, hallucinations, anxiety, depression, paranoia, and other mental and mood changes, sometimes lasting for months after the last dose.
  • Drug resistance: The history of antimalarial medicine has been marked by a constant struggle between evolving drug-resistant parasites and the search for new drug formulations. Resistance can be caused by mutations in the genetics of the infecting agent, such as the Plasmodium species. The longer the species is exposed to the anti-malarial drug, the more likely the parasite will mutate and become resistant to the drug. In certain parts of the world, for instance, resistance to chloroquine has rendered the drug ineffective. Currently, anti-malaria experts are focusing on therapies that combine artemisinin derivatives with other companion drugs, such as lumefantrine, sulfadoxine-pyrimethamine, amodiaquine (a drug similar to chloroquine), and mefloquine. Artemisin derivatives are not licensed for use in the United States, but are found overseas.
Prevention
  • Prevention is based on avoiding exposure to mosquitoes and aggressivelytreating those individuals who are infected. Malaria control programs, such as pesticide use, inmany parts of the world are under-funded and ineffective. Ifan individual is traveling to an area where malaria is common, taking antimalarialdrugs exactly as prescribed by a doctor is important. Also, it is recommended by healthcare professionals to prevent mosquitobites by: closing windows at night if possible; sleeping with a mosquitonet, preferably one containing an insecticide,with the edgestucked under the mattress; covering up the body as much aspossible with clothing; and applying an insect repellent to areasof the body not coveredby clothing.
  • For preventive treatment, individuals generally take the prescribed drug one to two weeks before leaving, throughout the trip, and for four weeks after return. Overdose of antimalarial drugs can be fatal, so following the prescription carefully is important. It is also important not to miss doses.
  • If the individual is pregnant, avoid traveling to malaria-endemic regions. If this is not possible, a doctor can prescribe an antimalarial drug that is appropriate for each individual, such as chloroquine or mefloquine (during the second or third trimester). Malarone® or doxycycline can harm the fetus.
References
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  6. National Institute of Allergy and Infectious Diseases. . Accessed April 14, 2009.
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