Understanding Malaria

by National Institute of Health

What is Malaria?

Malaria is a disease caused by a parasite that lives part of its life in humans and part in mosquitoes. worldwide, threatening the lives of more than one-third of the world's It remains one of the major killers of humans population. Malaria thrives in the tropical areas of Asia, Africa, and South and Central America, where it strikes millions of people. Sadly, as many as 2.7 million of its victims, mostly infants and children, die yearly.

Although malaria has been virtually eradicated in the United States and other regions with temperate climates, it continues to affect hundreds of people in this country every year. In 2000, health care workers reported 1,400 cases of malaria to the U.S. Centers for Disease Control and Prevention (CDC). Malaria in the United States is typically acquired during trips to malaria-endemic areas of the world and therefore is often called travelers' malaria.

During the past 10 years, CDC has documented local cases of malaria in states as varied as California, Florida, Texas, Michigan, New Jersey, and New York. In the summer of 1999, one highly publicized case occurred at a Boy Scout camp on Long Island, New York, where two boys were infected by mosquitoes.

History of Malaria

Malaria has been around since ancient times. The early Egyptians wrote about it on papyrus, and the famous Greek physician Hippocrates described it in detail. It devastated the invaders of the Roman Empire. In ancient Rome, as in other temperate climates, malaria lurked in marshes and swamps. People blamed the unhealthiness in these areas on rot and decay that wafted out on the foul air, or, as the Italians were to say, "mal aria" or bad air. In 1880, scientists discovered the real cause of malaria, the one-celled Plasmodium parasite, and 18 years later, they attributed the transmission of malaria to the Anopheles mosquito.

Historically, the United States is no stranger to the tragedy of malaria. The toll that this disease, commonly known as "fever and ague," took on early settlers is vividly depicted in the popular children's book "Little House on the Prairie" by Laura Ingalls Wilder. Historians believe that the incidence of malaria in this country peaked around 1875, but they estimate that by 1914 more than 600,000 new cases still occurred every year. Malaria has been a significant factor in virtually all of the military campaigns involving the United States. In both World War II and the Vietnam War, more personnel time was lost due to malaria than to bullets.

The malaria parasite typically is transmitted to humans by mosquitoes belonging to the genus Anopheles. In rare cases, a person may contract malaria through contaminated blood, or a fetus may become infected by its mother during pregnancy. The larval stage of the Anopheles mosquito thrives in still waters, such as swamps. The discovery by scientists that mosquitoes carried the disease unleashed a flurry of ambitious public health measures designed to stamp out malaria. These measures were targeted at both the larval and adult stages of the insect. In some areas, such as the southern United States, draining swamps and changing the way land was used was somewhat successful in eliminating mosquitoes.

The pace of the battle accelerated rapidly when the insecticide DDT and the drug chloroquine were introduced during World War II. DDT was remarkably effective and could be sprayed on the walls of houses where adult Anopheles mosquitoes rested after feeding. Chloroquine has been a highly effective medicine for preventing and treating malaria.

In the mid-1950s, the World Health Organization (WHO) launched a massive worldwide campaign to eliminate malaria. At the beginning, the WHO program, which combined insecticide spraying and drug treatment, had many successes, some spectacular. In some cases, malaria was conquered completely, benefiting more than 600 million people, and it was sharply curbed in the homelands of 300 million others.

Difficulties soon developed, however. Some stumbling blocks were administrative, others financial. Even worse, nature had begun to intervene. More and more strains of Anopheles mosquitoes were developing resistance to DDT and other insecticides. Meanwhile, the Plasmodium parasite was becoming resistant to chloroquine, the mainstay of antimalarial drug treatment in humans.

Researchers estimate that infection rates increased by 40 percent between 1970 and 1997 in sub-Saharan Africa. To cope with this dangerous resurgence, public health workers carefully select prevention methods best suited to a particular environment or area. include such standbys as draining swampy areas and filling them with dirt, and using window screens, mosquito netting, and insect repellents.

At the same time, scientists are intensively researching ways to develop better weapons against malaria, including sophisticated techniques for tracking disease transmission worldwide, more effective ways of treating malaria, new ways, some quite ingenious, to control transmission of malaria by mosquitoes, a vaccine for blocking its development and spread.

About the Author

NIH is the nation's medical research agency - making important medical discoveries that improve health and save lives. The National Institutes of Health (NIH), a part of the U.S. Department of Health and Human Services, is the primary Federal agency for conducting and supporting medical research.