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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. 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
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