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Malaria
Malaria is an infectious disease caused by a parasite, Plasmodium, which
infects red blood cells. Plasmodium is a type of protozoa, a single-celled
organism that is able to divide only within a host cell. The main types of
Plasmodium are P. falciparum, the species that causes falciparum malaria,
the most dangerous type of malaria; P. malariae, the species that causes
quartan malaria; P. ovale, a species found primarily in east and central
Africa that causes ovale malaria; and P. vivax, the species that causes
vivax malaria, which tends to be milder than falciparum malaria.
Malaria is characterized by cycles of chills, fever, pain, and sweating.
Historical records suggest malaria has infected humans since the
beginning of mankind. The name "mal aria" (meaning "bad air" in Italian)
was first used in English in 1740 by H. Walpole when describing the
disease. The term was shortened to "malaria" in the 20th century. C.
Laveran in 1880 was the first to identify the parasites in human blood. In
1889, R. Ross discovered that mosquitoes transmitted malaria. Of the four
common species that cause malaria, the most serious type is Plasmodium
falciparum malaria. It can be life-threatening. However, another relatively
new species, Plasmodium knowlesi, is also a dangerous species that is
typically found only in long-tailed and pigtail macaque monkeys. Like P.
falciparum, P. knowlesi may be deadly to anyone infected. The other three
common species of malaria (P. vivax, P. malariae, and P. ovale) are
generally less serious and are usually not life-threatening. It is possible to
be infected with more than one species of Plasmodium at the same time.
Currently, about 2 million deaths per year worldwide are due to
Plasmodium infections. The majority occur in children under 5 years of age
in sub-Saharan African countries. There are about 400 million new cases
per year worldwide. Most people diagnosed in the U.S. obtained their
infection outside of the country, usually while living or traveling through an
area where malaria is endemic.
What are malaria symptoms and signs?
The symptoms characteristic of malaria include flulike illness with fever.
Chills, muscle aches, and headache. Some patients develop nausea,
vomiting, cough, and diarrhea. Cycles of chills, fever, and sweating that
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repeat every one, two, or three days are typical. There can sometimes be
vomiting, diarrhea, coughing, and yellowing (jaundice) of the skin and
whites of the eyes due to destruction of red blood cells and liver cells.
People with severe P. falciparum malaria can develop bleeding problems,
shock, liver or kidney failure, central nervous system problems, coma, and
can die from the infection or its complications. Cerebral malaria (coma, or
altered mental status or seizures) can occur with severe P. falciparum
infection. It is lethal if not treated quickly; even with treatment, about 15%20% die.
How is malaria transmitted?
The life cycle of the malaria parasite (Plasmodium) is complicated and
involves two hosts, humans and Anopheles mosquitoes. The disease is
transmitted to humans when an infected Anopheles mosquito bites a
person and injects the malaria parasites (sporozoites) into the blood. This
is shown in Figure 1, where the illustration shows a mosquito taking a blood
meal (circle label 1 in Figure 1).
Figure 1: CDC illustration of the life cycles of malaria parasites,
Plasmodium spp. SOURCE: CDC
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Sporozoites travel through the bloodstream to the liver, mature, and
eventually infect the human red blood cells. While in red blood cells, the
parasites again develop until a mosquito takes a blood meal from an
infected human and ingests human red blood cells containing the parasites.
Then the parasites reach the Anopheles mosquito's stomach and
eventually invade the mosquito salivary glands. When an Anopheles
mosquito bites a human, these sporozoites complete and repeat the
complex Plasmodium life cycle. P. ovale and P. vivax can further
complicate the cycle by producing dormant stages (hypnozoites) that may
not develop for weeks to years.
What is the incubation period for malaria?
The period between the mosquito bite and the onset of the malarial illness
is usually one to three weeks (seven to 21 days). This initial time period is
highly variable as reports suggest that the range of incubation periods may
range from four days to one year. The usual incubation period may be
increased when a person has taken an inadequate course of malaria
prevention medications. Certain types of malaria (P. vivax and P. ovale)
parasites can also take much longer, as long as eight to 10 months, to
cause symptoms. These parasites remain dormant (inactive or hibernating)
in the liver cells during this time. Unfortunately, some of these dormant
parasites can remain even after a patient recovers from malaria, so the
patient can get sick again. This situation is termed relapsing malaria.
The classic and most used diagnostic test for malaria is the blood smear on
a microscope slide that is stained (Giemsa stain) to show the parasites
inside red blood cells (see Figure 2).
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Figure 2: CDC slide of a Giemsa stained smear of red blood cells showing
Plasmodium malariae and Plasmodium falciparum parasites. SOURCE:
CDC/Steven Glenn, Laboratory & Consultation Division
Although this test is easily done, correct results are dependent on the
technical skill of the lab technician who prepares and examines the slides
with a microscope.
Is malaria a particular problem during pregnancy?
Yes. Malaria may pose a serious threat to a pregnant woman and her fetus.
Malaria infection in pregnant women may be more severe than in women
who are not pregnant. Malaria may also increase the risk of problems with
the pregnancy, including prematurity, abortion, and stillbirth. Statistics
indicate that in sub-Saharan Africa, between 75,000-200,000 infants die
from malaria per year; worldwide estimates indicate about 2 million children
die from malaria each year. Therefore, all pregnant women who are living
in or traveling to a malaria risk area should consult a doctor and take
prescription drugs (for example, sulfadoxine-pyrimethamine) to avoid
contracting malaria.
How do people avoid getting malaria?
If people must travel to an area known to have malaria, they need to find
out which medications to take, and take them as prescribed. Current CDC
recommendations suggest individuals begin taking antimalarial drugs about
one to two weeks before traveling to a malaria infested area and for four
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weeks after leaving the area (prophylactic or preventative therapy).
Doctors, travel clinics, or the health department can advise individuals as to
what medicines to take to keep from getting malaria. Currently, there is no
vaccine available for malaria, but researchers are trying to develop one.
Avoid travel to or through countries where malaria occurs if possible. If
people must go to areas where malaria occurs, they should take all of the
prescribed preventive medicine. In addition, the 2010 CDC international
travel recommendations suggest the following precautions be taken in
malaria and other disease-infested areas of the world; the following CDC
recommendations are not unique for malaria but are posted by the CDC in
their malarial prevention publication.

Avoid outbreaks: To the extent possible, travelers should avoid
traveling in areas of known malaria outbreaks. The CDC Travelers'
Health web page provides alerts and information on regional disease
transmission patterns and outbreak alerts (http://www.cdc.gov/travel).

Be aware of peak exposure times and places: Exposure to arthropod
bites may be reduced if travelers modify their patterns of activity or
behavior. Although mosquitoes may bite at any time of day, peak biting
activity for vectors of some diseases (for example, dengue,
chikungunya) is during daylight hours. Vectors of other diseases (for
example, malaria) are most active in twilight periods (for example, dawn
and dusk) or in the evening after dark. Avoiding the outdoors or
focusing preventive actions during peak hours may reduce risk.

Wear appropriate clothing: Travelers can minimize areas of exposed
skin by wearing long-sleeved shirts, long pants, boots, and hats.
Tucking in shirts and wearing socks and closed shoes instead of
sandals may reduce risk. Repellents or insecticides such as permethrin
can be applied to clothing and gear for added protection; this measure
is discussed in detail below.

Check for ticks Travelers should be advised to inspect themselves and
their clothing for ticks during outdoor activity and at the end of the day.
Prompt removal of attached ticks can prevent some infections.
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
Bed nets: When accommodations are not adequately screened or air
conditioned, bed nets are essential to provide protection and to reduce
discomfort caused by biting insects. If bed nets do not reach the floor,
they should be tucked under mattresses. Bed nets are most effective
when they are treated with an insecticide or repellent such as
permethrin. Pretreated, long-lasting bed nets can be purchased prior to
traveling, or nets can be treated after purchase. The permethrin will be
effective for several months if the bed net is not washed. (Long-lasting
pretreated nets may be effective for much longer.)

Insecticides: Aerosol insecticides, vaporizing mats, and mosquito coils
can help to clear rooms or areas of mosquitoes; however, some
products available internationally may contain pesticides that are not
registered. Insecticides should always be used with caution, avoiding
direct inhalation of spray or smoke.

Optimum protection can be provided by applying repellents. The CDC
recommended insect repellent should contain up to 50% DEET (N,Ndiethyl-m-toluamide), which is the most effective mosquito repellent for
adults and children over 2 months of age.
What is the prognosis (outcome) for people with malaria?
The majority of people who become infected with P. malariae, vivax, or
ovale do well and the fevers abate after about 96 hours. However, in
endemic areas, reinfection is common. Malaria caused by P. falciparum or
P. knowlesi, even when treated, have outcomes ranging from fair to poor,
depending on how the parasites react to treatment. Untreated people often
die from these infections. In general, patients who are infants, children
under the age of 5 (especially in sub-Saharan countries), and those with
depressed immune systems (for example, AIDS or cancer patients) have a
more guarded prognosis.
Where can people get more information about malaria?
"The History of Malaria, an Ancient Disease," Centers for Disease Control and Prevention
"About Malaria," Centers for Disease Control and Prevention
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