Malaria

Malaria

Definition

Malaria is an infectious disease caused by a parasite that spends part of its

life cycle in humans and part in mosquitoes.

Description

Malaria is a potentially fatal disease that has infected humans as far back

as 50,000

Egypt in 2700

from the same period describe the symptoms of the disease. The English

name of the disease comes from an eighteenth-century Italian doctor

who wrote a textbook about it and attributed it to bad air, or

BCE. There are records of mosquito netting being used inBCE to protect against malaria. Chinese medical recordsmal’aria

in Italian.

Humans develop malaria when they are infected with a protozoan

called

the bloodstream and are carried to the liver, where they infect liver cells

and multiply. The mature parasites are released back into the bloodstream,

where they infect red blood cells. The red cells burst in two to

three days, releasing more parasites that, in turn, invade more red blood

cells. Most of the symptoms of malaria (fever,

chills, generally sick or flu-like feeling) are

related to the destruction of red blood cells. The

reason why the fever associated with malaria

comes in two- or three-day cycles in some people

is that the bursting of infected red blood cells

and the infection of new red blood cells occurs

every two to three days.

There are four different species of

Plasmodium

that infect people. One of these,

falciparum

other three. It can cause failure of the lungs, kidneys, and central nervous

system within a few hours or days. The different species also take different

lengths of time to produce the first symptoms of malaria in

humans. Some remain in the liver for long periods of time, thus causing

flare-ups of the disease months or even years later. These variations are

one reason why doctors try to identify the particular

when they test a person

be infected with more than one species of the parasite at the same time.

People cannot get malaria from sharing a household with an infected

person since it takes more than a week before a mosquito is able to

transmit the disease. It is possible for a pregnant woman to transmit the

disease to her unborn baby, however. It is also possible to get malaria

through a transfusion of infected blood, but this form of transmission

is rare in developed countries. In the United States, people who have traveled

in an area with endemic malaria cannot donate blood for a full year

after returning to the United States. They are forbidden to donate blood

for three years if they have been treated for malaria.

Plasmodium, is much deadlier than thePlasmodium species’s blood for malaria. It is possible for a person to

Demographics

Malaria is one of the most common infectious diseases in tropical and

subtropical parts of the world. These countries account for 41 percent

of the world

900 million cases of malaria around the world each year and 1 million to

3 million deaths, most of them African children under age five. In some

parts of Africa, it is estimated that one person dies of malaria every thirty

seconds. The disease is endemic in parts of Africa, southern Asia, and

portions of South America.

Malaria has not been endemic in the United States since 1951, when

a four-year program was started in 1947 to spray areas in the southeastern

part of the country that were known to harbor the mosquitoes

that transmit malaria. By 1952 the Centers for Disease Control and Prevention

(CDC) reported that malaria had been eradicated from the

United States. Cases of malaria since that time were either acquired by

people traveling to countries where malaria is endemic or were small local

outbreaks caused by local mosquitoes biting infected travelers and then

transmitting the malaria parasites to others nearby. In 2002 the CDC

reported 1,337 cases of malaria in the United States, including eight

deaths. All but five cases were acquired abroad.

People who are at greatest risk for malaria are those who have never

been exposed to the disease, pregnant women, and young children. Some

researchers also think that genetic factors may increase some people

of getting the disease.

’s risk

Causes and Symptoms

The cause of malaria is a protozoan of the genus

deadly of the four species that can cause malaria in humans is

falciparum

of chills and shaking followed by fever and sweating lasting four to six

hours. People infected by

as well. In some cases, the early symptoms of malaria may be mistaken

for the flu.

Children infected by

on the brain and suffer permanent brain damage even if they survive.

Adults infected by

dehydration, an enlarged liver and spleen, rupture of the spleen, severe

headache, loss of blood supply to the brain, and coma. Some die. The

destruction of red blood cells by the parasite may cause the urine to look

brown or black, which is why the disease got the name

fever.

Plasmodium. The mostPlasmodium. The classical symptom of malaria is a repeated cycleP. falciparum may feel a tingling in the skinP. falciparum may develop increased fluid pressureP. falciparum may develop kidney failure,“blackwater”

Diagnosis

Diagnosis of malaria is based on a combination of the patient

and the results of blood tests. The patient

the dates of any trips abroad, because two of the four species of

the malaria parasite can remain dormant in the liver for months or

even years.

The basic blood test involves looking at blood smears made by

pricking the patient

technique is called a thick smear, which is used to estimate the number of

parasites in the blood. The other is called a thin smear and is used to

determine the species. A rapid test called OptiMAL has been developed

to distinguish

time than the smear method and can be used by doctors in areas without

hospital laboratories.

’s finger at twelve- to twenty-four-hour intervals. OneP. falciparum from the other species. It gives results in less

Treatment

Malaria is treated with various combinations of drugs, which may be

given by mouth or intravenously. Patients infected by

be taken to a hospital for treatment because of the possibility of major

organ damage. The oldest drugs used to prevent or treat malaria are quinine

and chloroquine. Relatively inexpensive, they are not always effective

because the malaria parasites have developed resistance to them in

some countries. Newer drugs have been developed that are more effective

for resistant strains. People who are traveling to parts of the world where

malaria is endemic need to take these drugs while they are abroad.

The specific drug that is given to a patient and the length of treatment

depend on the type of malaria, the source of the infection, the

patient

People often feel weak and tired for a few weeks when taking these

medications.

P. falciparum may’s age, and the severity of the symptoms when treatment began.

Prognosis

Malaria caused by

of the first symptoms. In some areas, the death rate from this type of

malaria is as high as 20 percent. People infected by the other three species

of

months until all the parasites have been cleared from their livers.

P. falciparum is the most deadly; it can kill within daysPlasmodium usually recover, but some may have bouts of malaria for

Prevention

There is no vaccine effective against the malaria parasite, although scientists

are working on several possibilities. For the time being, prevention is

the most effective way to lower one

three basic strategies recommended by the CDC:

’s risk of getting malaria. There are

•

draining swampy areas. This approach is called vector control.

Controlling the mosquito population by using insecticides and

•

other sleeping areas. These nets have cut the number of deaths

from malaria in parts of Africa by 20 percent.

Using mosquito netting treated with insecticide to cover beds and

•

where malaria is endemic. The CDC has general advice for travelers

and a list of countries where travelers are at risk for malaria at

http://www.cdc.gov/malaria/travel/index.htm.

Taking medications to prevent the disease when visiting countries

The Future

It is unlikely that the mosquitoes that carry malaria will ever be completely

wiped out. At present, efforts to relieve the impact of malaria in Africa

are aimed at preventing the disease. Methods include spraying insecticides,

providing people with insecticide-treated mosquito netting, and

supplying poor countries with antimalarial drugs. In 2005 the President

Malaria Initiative (PMI)

the National Institutes of Health, the World Health Organization, and

the World Bank as well as the White House

to cut deaths from malaria by 50 percent in fifteen African countries.

The most promising area of malaria research as of 2008 was the development

of vaccines against the disease. Scientists have identified the

genetic sequence of the malaria parasite, which may help researchers target

a particular stage in the life cycle of the parasite or prevent it from developing

inside the mosquito. One possibility is developing a vaccine that

would stop the parasite inside the human body before it gets to the point

of infecting the red blood cells. Another group of researchers is experimenting

with cultivating

parasite with radiation in order to make a vaccine. This approach is

described in the video listed below.

’s—a cooperative program that involves the CDC,—began a five-year programP. falciparum inside mosquitoes and treating the

SEE ALSO

Influenza; Syphilis; West Nile virus infection

For more information

BOOKS

Abramovitz, Melissa. Malaria. Detroit, MI: Lucent Books, 2006.

Lynette, Rachel.

Marcus, Bernard A.

Malaria. Farmington Hills, MI: KidHaven Press, 2006.Malaria. Philadelphia: Chelsea House Publishers, 2004.

PERIODICALS

Appleton, Samantha.

2005. Available online at http://www.newyorker.com/archive/2005/10/24/

slideshow_051024?slide=1#showHeader (accessed April 24, 2008). This is a

slide show of fifteen photographs of the 2005 malaria epidemic in Africa.

McNeil, Donald G., Jr.

December 11, 2007. Video available online at http://video.on.nytimes.com/

index.jsp?fr_story=6e4647e2867283dce5b8cb2cf46003e7fdcd6267

(accessed April 25, 2008). This is a four-minute video about ongoing efforts

to develop a vaccine against malaria.

“Slide Show: Healing Africa.” New Yorker, October 24,“Searching for a Cure for Malaria.” New York Times,

WEB SITES

Centers for Disease Control and Prevention (CDC).

Available online at http://www.cdc.gov/malaria/ (updated April 18, 2008;

accessed April 24, 2008). Contains links to news items as well as basic

information about malaria and its treatment.

Mayo Clinic.

malaria/DS00475 (updated February 8, 2008; accessed April 25, 2008).

President

fightingmalaria.gov/resources/pmi_fastfacts.pdf (posted January 2008;

accessed April 26, 2008).

Sumanas, Inc.

online at http://www.sumanasinc.com/scienceinfocus/sif_malaria.html

(accessed April 5, 2008). This is an animation of the life cycle of the malaria

parasite with voiceover. It takes three minutes to play.

WGBH Educational Foundation.

www.pbs.org/wgbh/rxforsurvival/series/diseases/malaria.html (posted 2005;

accessed April 24, 2008). The right-hand side of the page includes links to

three videos on malaria, each about five minutes in length.

WORDS TO KNOW
Dementia: Loss of memory and other mental
functions related to thinking or problem-solving.
Endemic: A term applied to a disease that
maintains itself in a particular area without
reinforcement from outside sources of infection.
Protozoan (plural, protozoa): A one-celled animallike
organism with a central nucleus enclosed by
a membrane. Many protozoa are parasites that
can cause disease in humans.
Spleen: An organ located behind the stomach that
cleans old blood cells out of the blood and holds
a reserve of red blood cells.
Vector: An insect or other animal that carries a
disease from one host to another.

Malaria Research and the Nobel Prize

One indication of the importance

complexity

prizes in medicine that have been awarded to

doctors who studied the disease. Charles Louis

Alphonse Laveran (1845

doctor working in a military hospital in Algeria in

1880 when he discovered that malaria is caused by

a protozoan (a type of one-celled organism). This

was the first time that a protozoan had been

shown to cause any disease in humans. Laveran

was awarded the Nobel Prize in Physiology or

Medicine in 1907.

In 1898, Sir Ronald Ross (1857

doctor working in India, was able to show that

mosquitoes are the vectors that carry malaria to

humans. Ross even demonstrated that the parasites

are present in the mosquito

He was awarded the Nobel Prize in Physiology or

Medicine in 1902. Austrian doctor Julius Wagner-

Jauregg (1857

He showed that malaria could actually be used to

treat patients suffering from late-stage syphilis, a

common cause of dementia in the early twentieth

century. The reason this treatment was thought to

work was that the fever caused by the malaria

parasite was high enough to kill the bacteria that

cause syphilis.

The fourth Nobel Prize in Physiology or Medicine

related to malaria research was given in 1948 to

Paul Hermann Müller (1899

chemist who discovered dichloro-diphenyltrichloroethane

(DDT) in 1939. DDT was the first

insecticide that was effective in controlling the

mosquitoes that spread malaria.

—and the—of malaria is the number of Nobel–1922) was a French–1932), a British’s salivary glands.–1940) won a Nobel prize in 1927.–1965), a Swiss

Malaria: Topic Home.Malaria. Available online at http://www.mayoclinic.com/health/’s Malaria Initiative (PMI). Fast Facts. Available online at http://www.Malaria: Cooperation among Parasite, Vector, and Host. AvailableRx for Survival: Malaria. Available at http://’s history’s history is critical, particularly’s population. It is estimated that there are between 400 andPlasmodium through the bite of a mosquito. The parasites enter