at curiositystream.com/realscience and get free access to watchnebula.com

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. And when we

think of malaria we probably think of humid jungles or tropical lakes in

equatorial regions. As of 2017, 87 countries had ongoing malaria

transmission, with places like the US and Europe appearing to be safely off the

list. It's easy to assume that's because the US and Europe are not tropical

places. But in fact, both places used to be riddled with malaria. In the U.S. in

particular, it debilitated towns, caused thousands of deaths, and even determined

the settlement patterns of the country. But now it has been so thoroughly erased

that many people don't even know it used to exist there at all. So how is it that

malaria once thrived in the US, and why did it disappear? And perhaps most

importantly, can the methods of its elimination in the US be copied

elsewhere? To understand the spread of malaria in the US it's important to

consider the life cycle and behavior of the Plasmodium parasite and it's 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 a small amount of blood is taken in which contains

microscopic malaria parasites, which then mate in the gut of the mosquito and begin

a cycle of growth and multiplication. About one week later, a form of the

parasite called a sporozoite migrates to the mosquitos salivary

glands. When the mosquito takes its next blood meal these parasites mix with the

mosquitos saliva and are injected into the next person being bitten.

The sporozoites then rides in the bloodstream towards the human liver. Once

it arrives, it enters a liver cell. There it undergoes 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 hide from 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 they are inhabiting ruptures and the new

parasites called merozoite are released. These continue the cycle by invading

other red blood cells which subsequently also rupture. The parasites living in the

bloodstream is what causes the symptoms of malaria, which can range from

headaches, to fever, to seizures, to death if the parasites block arteries in the

brain and kidneys. At this point the parasite within the human bloodstream

can then be ingested once again by a mosquito and transmitted to another

unsuspecting human and the cycle begins again. No one knows for sure when malaria

was first introduced into humans but it is thought to have been in prehistoric

times. But as for the US its infestation with the disease was not

brought about until the 17th century with the first 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 were initially thought of as a land of

paradise by European settlers but with the introduction of malaria became known

as a ghastly place to live. An English proverb at the time said "those who want

to die quickly, go to Carolina". Incoming immigrants thus labeled certain

colonies as healthy and others as dangerous. The Caribbean was understood

to be the most dangerous, with Florida and the Carolinas being a close second.

The Chesapeake was a bit better but only in the northern colonies - New York, New

England, and Pennsylvania, did European settlers thrive. And because most African

slaves had some tolerance to malaria and white indentured laborers from Europe

did not, demand for slave labor in malarious areas also increased. Malaria,

along with other diseases like yellow fever, thus had 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 the first world war,

malaria was a huge problem, especially for the military, where men training in

the south were picking up the disease in rapid numbers. 10,500 admissions for

malaria were reported from April 1917 through December 1919, involving a loss

of 130,000 training days. By the 1930s malaria had

become concentrated in 13 of the country's southeastern states and there

were well over a million cases during the Great Depression. Malaria had become

a major national problem. By 1933, malaria deaths in America reached a new peak.

Malaria thrives when poverty is high where people lack access to adequate

health care and nutrition, and America had just descended into the Great

Depression. But for the next decade where malaria should have boomed, it instead

retreated. But the exact reason why isn't as clear as you might think. To this day

scientists and historians fiercely argue about which of the many factors was the

key to its eradication. At the time there were two camps of opinion on the best

way to get rid of malaria. The first, to attack the parasite inside the human

body. The second, to eliminate the vector for the disease, the mosquito. If it were

possible to treat all members of a community at once and eradicate the

parasite within them, then malaria could be wiped out, even if the adult

mosquitoes carry on biting everyone. For hundreds of years

people were aware that quinine obtained from cinchona bark could be used to

alleviate the symptoms of and even prevent malaria. So in 1916 scientists

carried out a study on 500,000 people in Bolivar County Mississippi,

a place plagued with malaria, to see if quinine could be used as an effective

treatment. They gave out doses of quinine for free and indeed found that it

reduced malaria infections by 90%. However even though high doses of

quinine were good for quickly ending an episode of fever and chills they found

that people would not take enough quinine on a regular basis to prevent

infection long term because of its bad side effects.

Therefore, it was useful for interrupting and infection and relieving symptoms but

more often than not the infection would just come right back. Thus quinine

distributed in large numbers definitely helped but it would not be the complete

answer to getting rid of malaria in America. It would take more than

medicating the population to get rid of this persistent disease. Once it became

known that the mosquito was the cause of malaria many people believed its death

would be the way to eliminate the disease. But killing the adult stage of

the mosquito is challenging since they infest the world in 3d space and at the

time there wasn't any reliable methods for doing so. Therefore many believed it

was best to attack the mosquito at the most vulnerable point in its lifecycle -

the larval stage. Mosquitoes lay their eggs in marshy stagnant water which then

hatch into larvae which will eventually develop into full-grown malaria

spreading mosquitoes. And so one way to hit them where it hurts is to eliminate

their breeding grounds, the marshy stagnant water. And unluckily for the

mosquitoes the 1930s brought a wave of public works projects intended to boost

the economy, including malaria control and lots and lots of digging. The Works

Progress Administration put people to work digging 32,000 miles of ditches and

draining 623,000 watered acres. And when draining wasn't possible, coating the

surfaces of ponds with oil and spraying their habitats with a compound called

Paris green further smothered the larvae. These efforts coincided with a sharp

decline in malaria transmission in the 1930s, but by 1940 while less common than

it once was, malaria still persisted.

During this time the US army still trained its men in many areas of the

Southeast US where malaria still had its grip. Not wanting to repeat the hard

lessons from the First World War, large-scale anti malaria operations were

undertaken. 40,000 acres of surface water was eliminated 4.7 million gallons of

diesel oil larvacide was used, and 9.8 million dollars was spent on this

all-out war against malaria. Then 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 US had dropped significantly and the disease's days in

the US were numbered. Then in 1946, the CDC was born, with the

primary mission of finally getting rid of 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 even more wetland drainage pushed the disease out of

existence. By 1951 malaria was considered eliminated altogether from the country.

The onslaught of DDT, drainage works, habitat oiling, and preventive medication

had finally worked. However there are dozens of other factors which also

contributed to malaria's death in America. Some historians firmly believe

that the key factor in its eradication was actually population movement away

from rural areas, while others think it was simply better education about the

disease that did the trick. Others think it was general economic improvement and

the installation of screens on houses, and yet others think it was actually a

massive drought that led to malaria's demise. This multivariable attack on the

disease and the uncertainty that that causes has left scientists unsure of how

to best translate these results to other parts of the world today. This, along with

the fact that many of the approaches taken in America cannot or should not be

taken in other parts of the world has made eliminating malaria globally a

massive, still unsolved problem. Most can agree that draining marshy areas in

America helped lead to malaria's decline in some amount. However, in Africa where

most of the world's cases of malaria occur today, such methods are not

feasible, because the mosquitoes there breed in small pools of water that

form from rainfall, spread across the landscape. It is difficult if not

impossible to predict when and where the breeding sites will form and to find and

treat them before the adult mosquitoes emerge.

DDT too was instrumental in eliminating malaria in America since it's so

effective at killing mosquitoes. The problem is we now know it's also great

at killing everything else. It was banned pretty much everywhere in the world in

the 1970s and 80s, and although it's still being used in some places

scientists urged it to be used as a last resort to combat malaria. Distributing

anti malaria medicine also would certainly help if everyone vulnerable to

the disease had plentiful access to it but the cost of this can be prohibitive

and while some progress can be made with this method the geography of places like

Africa make it so even if you make gains in one area, the disease will just pop

back up again as it returns from a surrounding area. These problems along

with new drug and insecticide resistance within the parasite and mosquito makes

it so new approaches must be taken in this global battle.

Luckily organizations like the Bill and Melinda Gates Foundation are working

towards just that putting their resources in large part towards better

data collection along with research and development for creating new medicines

and vaccines. And recently scientists have been experimenting with genetically

modified mosquitoes intended to drastically reduce mosquito populations

in the wild. It's a drastic new development in the battle against

mosquito-borne illness and is something we'll cover in depth in a future video.

No single strategy to combat malaria will ever be effective everywhere and

unfortunately there's no silver bullet for this centuries-old problem. But with

long term commitment and a flexible strategy along with much more funding it

may be possible to eliminate malaria everywhere in the world

one day soon. Malaria was in part wiped out in America

because of effective military strategy - a strategy that took thousands of

man-hours and millions of dollars and at the time seemed impossible. There have

been many unlikely achievements like this throughout history, from malaria and

yellow fever eradication in different parts of the world, to the building of

the Panama Canal, to the successful invasion of Normandy on D-Day, all things

which took unprecedented levels of coordination and strategy, and all things

that easily could have failed with the wrong plans set in motion. You can learn

more about the detailed logistics for operations like this in Real

Engineering's new Logistics of D-Day series available exclusively on Nebula,

the streaming platform made by the best educational content creators like

Wendover Productions, Medlife Crisis, BrainCraft and our other channel Real

Engineering. The great thing about Nebula is all of the original content, content

that we can create with total freedom without worrying about the YouTube

algorithm or demonetization. The next episode of Real Engineering's Logistics

of D-Day series is out today, and an episode of working titles will be coming

from me early next year, which if you don't know is a collaborative series

where different YouTube creators break down their favorite TV show intro.

Medlife Crisis did an episode on House, Polyphonic did one on Game of Thrones,

and I'll be doing one on Westworld. Wendover productions also just released

a 45 minute documentary about one of the world's most remote islands. There is so

much original content with more coming in all the time and to make it even

better Nebula has partnered with CuriosityStream. CuriosityStream is a

streaming platform that has thousands of high quality and high budget

documentaries like this series about the spread and effect ebola has had on

Africa and the rest of the world. If you're interested in science topics like

this CuriosityStream has a vast library of topics ranging from physics and

nature but also things like history and economics.