Malaria is a serious and sometimes fatal disease caused by a parasite that commonly infects a certain type of mosquito which feeds on humans. 

Four kinds of malaria parasites infect humans: Plasmodium falciparum, P. vivax, P. ovale, and P. malariae. In addition, P. knowlesi, a type of malaria that naturally infects macaques in Southeast Asia, also infects humans, causing malaria that is transmitted from animal to human ("zoonotic" malaria). 

Usually, people get malaria by being bitten by an infective female Anopheles mosquito. Only Anopheles mosquitoes can transmit malaria and they must have been infected through a previous blood meal taken from an infected person. When a mosquito bites an infected person, a small amount of blood is taken in which contains microscopic malaria parasites. About 1 week later, when the mosquito takes its next blood meal, these parasites mix with the mosquito's saliva and are injected into the person being bitten.

The symptoms will vary depending on the type of malarial infection.

Uncomplicated Malaria

The classical (but rarely observed) malaria attack lasts 6-10 hours. It consists of:

• a cold stage (sensation of cold, shivering)
• a hot stage (fever, headaches, vomiting; seizures in young children)
• and finally a sweating stage (sweats, return to normal temperature, tiredness).

More commonly, the patient presents with a combination of the following symptoms:

• Fever
• Chills
• Sweats
• Headaches
• Nausea and vomiting
• Body aches
• General malaise

Severe Malaria

Severe malaria occurs when infections are complicated by serious organ failures or abnormalities in the patient's blood or metabolism. The manifestations of severe malaria include

• Cerebral malaria, with abnormal behavior, impairment of consciousness, seizures, coma, or other neurologic abnormalities
• Severe anemia due to hemolysis (destruction of the red blood cells)
• Hemoglobinuria (hemoglobin in the urine) due to hemolysis
• Acute respiratory distress syndrome (ARDS), an inflammatory reaction in the lungs that inhibits oxygen exchange, which may occur even after the parasite counts have decreased in response to treatment
• Abnormalities in blood coagulation
• Low blood pressure caused by cardiovascular collapse
• Acute kidney failure
• Hyperparasitemia, where more than 5% of the red blood cells are infected by malaria parasites
• Metabolic acidosis (excessive acidity in the blood and tissue fluids), often in association with hypoglycemia
• Hypoglycemia (low blood glucose). Hypoglycemia may also occur in pregnant women with uncomplicated malaria, or after treatment with quinine.

Severe malaria is a medical emergency and should be treated urgently and aggressively.

No. Malaria is not spread from person to person like a cold or the flu, and it cannot be sexually transmitted. You cannot get malaria from casual contact with malaria-infected people, such as sitting next to someone who has malaria.

Where malaria is found depends mainly on climatic factors such as temperature, humidity, and rainfall. Malaria is transmitted in tropical and subtropical areas, where

• Anopheles mosquitoes  can survive and multiply
• Malaria parasites can complete their growth cycle in the mosquitoes ("extrinsic incubation period").

Anyone can get malaria. Most cases occur in people who live in countries with malaria transmission. People from countries with no malaria can become infected when they travel to countries with malaria or through a blood transfusion (although this is very rare). Also, an infected mother can transmit malaria to her infant before or during delivery.

Treatment of malaria depends on many factors including disease severity, the species of malaria parasite causing the infection and the part of the world in which the infection was acquired. The latter 2 characteristics help determine the probability that the organism is resistant to certain antimalarial drugs. Additional factors such as age, weight, and pregnancy status may limit the available options for malaria treatment.

• Learn about Malaria Treatment in the United States

CDC provides, on a 24-hour basis, consultations for clinicians needing guidance on diagnosis, management of malaria cases, access to antimalarial medication, or urgent issues related to adverse antimalarial drug reactions.

Assistance can be provided through the CDC Malaria Hotline (770-488-7788) from 9:00 am to 5:00 pm Eastern Time. After hours or on weekends and holidays, call the CDC Emergency Operation Center at 770-488-7100 and ask to page the person on call for the Malaria Branch. Do not use email to ask for clinical advice; email is not constantly monitored and there may be delays in answering.

You and your family can most effectively prevent malaria by taking all three of these important measures:

• Taking antimalarial medication to kill the parasites and prevent becoming ill
• Keeping mosquitoes from biting you, especially at night
• Sleeping under insecticide-treated bed nets, using insect repellent, and wearing long-sleeved clothing if out of doors at night.

Any traveler who becomes ill with a fever or flu-like illness while traveling, and up to 1 year after returning home, should immediately seek professional medical care. You should tell your health-care provider that you have been traveling in an area where malaria transmission occurs and ask to be tested for malaria infection.

Outbreaks of locally transmitted cases of malaria in the United States have been small and relatively isolated, but the potential risk for the disease to re-emerge is present due to the abundance of competent vectors, especially in the southern states. At the request of the states, CDC assists in these investigations of locally transmitted mosquito-borne malaria.