How Malaria Was Eradicated In The U.S.

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Most of us probably think of malaria as a disease confined to the tropics. It thrives in Southeast Asia, the eastern Mediterranean, parts of Central and South America, and Africa, which carries most of the global malaria burden. When we think of malaria, we often envision humid jungles or tropical lakes in equatorial regions. As of 2017, 87 countries had ongoing malaria transmission, with places like the U.S. and Europe appearing to be safely off the list. It’s easy to assume that’s because the U.S. and Europe are not tropical places. However, both regions used to be riddled with malaria. In the U.S. in particular, it debilitated towns, caused thousands of deaths, and even influenced settlement patterns in the country. Now, it has been so thoroughly erased that many people don’t even know it used to exist there at all.

So how did malaria once thrive in the U.S., and why did it disappear? More importantly, can the methods of its elimination in the U.S. be replicated elsewhere? To understand the spread of malaria in the U.S., it’s important to consider the life cycle and behavior of the Plasmodium parasite and its vector, the mosquito. Malarial parasites are carried by the Anopheles mosquito, which breeds in still water such as marshy ponds and swamps—features that exist in great numbers in the eastern and southern United States. When a mosquito bites an infected person, it takes in a small amount of blood containing microscopic malaria parasites, which then mate in the mosquito’s gut and begin a cycle of growth and multiplication. About one week later, a form of the parasite called a sporozoite migrates to the mosquito’s salivary glands. When the mosquito takes its next blood meal, these parasites mix with the mosquito’s saliva and are injected into the next person being bitten.

The sporozoites then travel in the bloodstream toward the human liver. Once they arrive, they enter a liver cell, where they undergo many rounds of division and multiplication. A single infected liver cell can lead to the creation of thousands of new parasites. These new parasites then migrate to infect red blood cells, where they can evade the body’s immune system. Here, they consume the contents of the red blood cell and divide to create even more parasites. Eventually, the red blood cell ruptures, releasing new parasites called merozoites. These continue the cycle by invading other red blood cells, which subsequently also rupture. The parasites in the bloodstream cause the symptoms of malaria, which can range from headaches and fever to seizures and death if the parasites block arteries in the brain and kidneys. At this point, the parasite within the human bloodstream can be ingested once again by a mosquito, and the cycle begins anew.

No one knows for sure when malaria was first introduced into humans, but it is thought to have been in prehistoric times. In the U.S., its introduction was not until the 17th century with the arrival of slave ships from Africa. Once the parasite was introduced to North American shores, places like the wet low-lying plains of Virginia and South Carolina became overrun with the disease. The Carolinas, initially viewed as a land of paradise by European settlers, became known as a ghastly place to live due to malaria. An English proverb at the time stated, “those who want to die quickly, go to Carolina.” Incoming immigrants labeled certain colonies as healthy and others as dangerous, with the Caribbean being the most hazardous, followed closely by Florida and the Carolinas. The Chesapeake region was somewhat better, but only in the northern colonies—New York, New England, and Pennsylvania—did European settlers thrive. Because most African slaves had some tolerance to malaria while white indentured laborers from Europe did not, demand for slave labor in malarious areas increased. Malaria, along with other diseases like yellow fever, played a substantial role in determining settlement and labor patterns in the colonies—patterns that would eventually lead to the Civil War.

Malaria wreaked havoc in America for centuries, and by the time of World War I, it was a significant problem, especially for the military, where men training in the South were contracting the disease in large numbers. From April 1917 through December 1919, there were 10,500 admissions for malaria, resulting in a loss of 130,000 training days. By the 1930s, malaria had become concentrated in 13 southeastern states, with well over a million cases during the Great Depression. Malaria had become a major national problem, and by 1933, malaria deaths in America reached a new peak. Malaria thrives when poverty is high, where people lack access to adequate healthcare and nutrition, and America had just descended into the Great Depression.

However, for the next decade, where malaria should have boomed, it instead retreated. The exact reason for this decline is still debated among scientists and historians. At the time, there were two main approaches to combat malaria: one focused on attacking the parasite inside the human body, and the other aimed to eliminate the mosquito vector. If it were possible to treat all members of a community at once and eradicate the parasite within them, malaria could be wiped out, even if adult mosquitoes continued to bite. For hundreds of years, people knew that quinine, obtained from cinchona bark, could alleviate symptoms and even prevent malaria. In 1916, scientists conducted a study on 500,000 people in Bolivar County, Mississippi, a place plagued with malaria, to see if quinine could be an effective treatment. They distributed doses of quinine for free and found that it reduced malaria infections by 90%. However, while high doses of quinine were effective for quickly ending episodes of fever and chills, people were reluctant to take it regularly due to its side effects. Thus, while quinine helped interrupt infections and relieve symptoms, the infection often returned.

Once it became known that mosquitoes were the cause of malaria, many believed that eliminating them would be the solution. However, killing adult mosquitoes is challenging since they inhabit three-dimensional spaces, and at the time, there were no reliable methods for doing so. Many believed it was best to target the mosquito at its most vulnerable point in its lifecycle—the larval stage. Mosquitoes lay their eggs in marshy stagnant water, which then hatch into larvae that eventually develop into adult mosquitoes. One effective strategy was to eliminate their breeding grounds. Fortunately for the mosquitoes, the 1930s brought a wave of public works projects aimed at boosting the economy, including malaria control efforts. The Works Progress Administration employed people to dig 32,000 miles of ditches and drain 623,000 acres of waterlogged land. When draining wasn’t possible, they coated pond surfaces with oil and sprayed habitats with a compound called Paris green to smother the larvae.

These efforts coincided with a sharp decline in malaria transmission in the 1930s. However, by 1940, while malaria was less common than before, it still persisted. During this time, the U.S. Army continued training in many areas of the Southeast where malaria remained a threat. Not wanting to repeat the hard lessons from World War I, large-scale anti-malaria operations were undertaken. They eliminated 40,000 acres of surface water, used 4.7 million gallons of diesel oil larvicide, and spent 9.8 million dollars in an all-out war against malaria. In 1944, one of the most effective mosquito killers of all time was invented—DDT. Thanks in part to DDT, by 1945, malaria transmission in the U.S. had dropped significantly, and the disease’s days in the country were numbered.

In 1946, the CDC was established with the primary mission of eradicating malaria in America once and for all. During the CDC’s first few years, more than 6.5 million homes were sprayed with DDT. This, along with further wetland drainage, pushed the disease out of existence. By 1951, malaria was considered eliminated altogether from the country. The combination of DDT, drainage works, habitat oiling, and preventive medication had finally worked. However, numerous other factors also contributed to malaria’s decline in America. Some historians believe that population movement away from rural areas was key, while others attribute it to better education about the disease, general economic improvement, or the installation of screens on houses. Some even suggest that a massive drought played a role in malaria’s demise.

This multifaceted approach to combating the disease and the uncertainty surrounding it has left scientists unsure of how to best apply these lessons to other parts of the world today. Many agree that draining marshy areas in America helped lead to malaria’s decline, but in Africa, where most of the world’s malaria cases occur today, such methods are not feasible. There, mosquitoes breed in small pools of water formed by rainfall, spread across the landscape. It is difficult, if not impossible, to predict when and where breeding sites will form and to treat them before adult mosquitoes emerge.

DDT was instrumental in eliminating malaria in America due to its effectiveness at killing mosquitoes. However, it is also known to harm other wildlife and was banned in many places during the 1970s and 80s. Although it is still used in some areas, scientists recommend it as a last resort to combat malaria. Distributing anti-malaria medicine could certainly help if everyone vulnerable to the disease had access to it, but the cost can be prohibitive. While some progress can be made with this method, the geography of regions like Africa means that even if gains are made in one area, the disease can re-emerge from surrounding regions. New drug and insecticide resistance in both the parasite and mosquito further complicates the situation, necessitating new approaches in this global battle.

Fortunately, organizations like the Bill and Melinda Gates Foundation are working towards solutions, focusing on better data collection and research and development for new medicines and vaccines. Recently, scientists have been experimenting with genetically modified mosquitoes designed to drastically reduce wild mosquito populations. This represents a significant new development in the fight against mosquito-borne illnesses and will be explored in depth in a future video.

No single strategy to combat malaria will be effective everywhere, and unfortunately, there is no silver bullet for this centuries-old problem. However, with long-term commitment, flexible strategies, and increased funding, it may be possible to eliminate malaria globally one day soon.

Malaria was largely eradicated in America due to effective military strategy—a strategy that required thousands of man-hours and millions of dollars and seemed impossible at the time. There have been many unlikely achievements throughout history, from the eradication of malaria and yellow fever in various regions to the construction of the Panama Canal and the successful D-Day invasion, all of which required unprecedented levels of coordination and strategy and could have easily failed with poor planning.

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