16. Malaria (I): The Case of Italy
Prof: I’d like to
welcome you back, and hope that you all had
really good breaks. We’ll be talking this week
about malaria, both today and on Wednesday.
And I think I may be saying a
couple of things that you may find surprising.
I suppose–this may be an
assumption– that when I mention malaria,
that most of you think of it as an exotic tropical disease,
and probably think that it’s very distant from us,
and has relatively little to do with the modern world,
or with modern history, and probably nothing at all to
do with the United States and with those of us here.
But the point I’m wanting to
make, this time and next, is that the reality of malaria
is quite different from that; that when we’ve come to talk
about this disease, I could say that of all human
diseases it’s one of the oldest; and some question,
a question that some of you might ask me,
is of all the diseases in our course,
which is the one that, in the aggregate,
has caused the most human suffering and death?
And I think that of all of the
diseases in our course, it’s probably malaria which has
that primacy. The relationship of human
beings to malaria has been so close,
and so extensive, that we could also say that we,
as a species, and malaria,
as a disease, have evolved together,
and that the human genome bears the imprint of our experience
with malaria. Good examples of that are a
couple of genetic diseases that I’d like to mention,
one that may be familiar to you also,
one being sickle-cell anemia, a second being thalassemia,
and a third being what’s called Duffy negativity.
Now, all of these are genetic
diseases, and they have in common the
feature that there’s a difference between the trait
which– it’s a recessive in all three
cases, the recessive features.
And, so, a heterozygote–that
is, a person who has just one X chromosome,
rather than X and Y, expressing the trait for the
disease– enjoys a protection from
malaria. But if, in fact,
you are a homozygote and have it on both X and Y chromosomes,
and you develop the syndrome for sickle-cell anemia,
instead you have a terrible disease that leads to–
it causes sickle cell–it affects the quality of the
hemoglobin and the red cells, and therefore it leads to
anemia, occlusion of blood vessels,
sometimes hypoxia, and serious respiratory
diseases. So, it’s a fatal illness in
many cases. But if you have the trait,
then in a highly malarial area you have a great selective
advantage in enjoying a great deal of resistance or immunity.
In terms of human evolution,
in intensely malarial areas there was a strong Darwinian
pressure for the retention of the sickle cell trait.
The same would be true of
thalassemia, which affects not the quality
of the red cells but rather their quantity,
and leads to again terrible complications in homozygotes,
and with asthma and terrible anemia,
or Duffy negativity, which is another genetic
disease that leads again to terrible diseases.
Another feature of malaria,
apart from the fact that our genome has actually been
strongly influenced by our history with malaria,
is that until very recently it extended more or less across the
globe, affecting not only the tropics
in Africa, Asia and South America,
but also the north, including most of Europe and
North America. So, I thought I’d show you a
map of malaria in the United States in the nineteenth
century, just to give you an idea–this
is 1882– to show how extensively
prevalent it was in this country,
as recently as the late nineteenth century.
And indeed it comes up–Oliver
Wendell Holmes wrote a book on malaria in New England.
This is a map of 1912,
when it’s receded a great deal and is primarily a disease of
the South. But remember that it had a
major impact on public health in this country,
until the end of the Second World War,
which is when it was eradicated in the United States.
It’s sobering to remember,
for example, that the Centers for Disease
Control, the CDC, in Atlanta,
was originally founded as an anti-malarial agency,
and that the disease played a major role in the settlement of
the West, and in the economic and social
development of the South. And if you read Mark Twain,
for example, you can read a great deal about
shivering along the banks of the Mississippi River.
In terms of our discussion of
relationship of diseases to the big picture of history,
malaria is also one of the diseases that I think helps us
to make the case most effectively.
Malaria, it’s now believed,
played a major part in the fall,
for example, of the Roman Empire,
when an epidemic of falciparum malaria led to
the disruption of agriculture and the Roman Legions.
And I’m not trying to say that
malaria caused the downfall of the Roman Empire.
I’m saying that it was a major
factor, leading to the kinds of
military problems and social dislocation that we can’t ignore
in discussing that major series of events.
It’s led to major impacts on
the outcome and on the conduct of warfare.
One need go back only to the
Second World War, when malaria was a major
preoccupation of the armies on both sides of the conflict.
It had an enormous role and
impact on European expansion and colonization,
and one of the great challenges to colonial expansion,
in the Indian subcontinent, and in Africa,
was what to do about the problem of malaria.
It’s affected the pattern of
human habitation and settlement, the way that cities and towns
are built across the landscape, where human habitation often
was a form of prophylaxis for malaria,
and people lived far from swampy areas,
and often on high ground, above dangerous wetlands low
down. Malaria is also a major factor
in economic development and under-development today,
in ways that we’ll be discussing.
A decisive factor in its
prevalence, and in its history, has always been the
relationship of human beings to agriculture and the environment;
that is to say that intensive forms of agriculture,
with modern livestock raising practices,
modern crop rotations, water management,
ecological sanitation, with improved housing and
conditions of diet, wages and clothing,
have led, wherever they’ve been introduced,
to a spontaneous recession of malaria and much better health
outcomes. And this has been a major
factor in the divergence between the global North and the global
South; the North with modernized
intensive systems of agriculture,
and in the South instead the persistence of extensive forms
of practice that are conducive, for reasons we’ll be examining,
to the transmission of malaria. So, malaria both reflects and
reinforces developmental differences and disparities.
Now, let’s remember that
malaria is vitally important in our world today.
Let me give you an example of
some of the pictures that represent the global burden of
malaria, and let me show you a map of
where malaria is prevalent today;
that is, in the twenty-first century.
Indeed, at the moment,
one can say the statistics are extraordinary.
About 500,000 people become
seriously ill of malaria every year.
Approximately a million people
die of it, the majority of them being
children under five, and pregnant women,
concentrated particularly in Sub-Saharan Africa.
In fact, one can say that a
child dies of malaria, in Africa today,
every thirty seconds, making this disease a global
public health emergency, along with HIV/AIDS and
tuberculosis. Let’s look at more particularly
the areas. This is the epicenter,
if you like, of the present day resurgence
of malaria as a major, major public health problem.
And there are–malaria kills
3,000 children every day of the year.
The burden of malaria though is
greater than statistics for mortality and morbidity suggest.
It is, for example,
one of the worst possible complications of pregnancy.
It leads to high rates of
miscarriage; to maternal death through
hemorrhaging and severe anemia, and all of the sequelae that
follow from severe low birth rate.
Malaria also can be transmitted
vertically; that is, trans-plancentally,
from mother to fetus, and can lead to the birth of
infants who are congenitally infected.
We also need to remember,
as we’ll say in a moment, that malaria is a major
immunosuppressive disease, and its victims therefore are
highly susceptible to other opportunistic infections;
especially respiratory infections, tuberculosis,
influenza, pneumonia. In those areas of the tropical
world where malaria is hyper-endemic,
and transmission continues throughout the year,
the population at risk can be infected,
re-infected and super-infected every single year.
If the victims of malaria
survive, they possess a painfully acquired immunity.
But it comes at a terrible
price, because repeated bouts of malaria lead to severe
neurological deficit and cognitive impairment.
The results are ineradicable
poverty, illiteracy and compromised economic growth,
a stunted development of civil society and political
instability. We’ll be talking in a moment
about Ronald Ross, who was the Nobel Laureate,
who was one of two people who discovered the mosquito theory
of transmission for disease. And he wrote,
quite movingly, that those malaria doesn’t–
in areas where malaria is prevalent–
“those it doesn’t kill it enslaves.”
Malaria, in other words,
in our present world, is a major contributor to
inequalities between North and South,
and to the economic and political international
dependency of third-world countries in the tropical world.
Well, let’s talk about
the–malaria also will be of interest to us because it’s an
extremely complex disease, and so we need to spend a
little bit of time talking about how it’s transmitted,
and about its effects on the human body,
in order, after that, to talk about how the
discoveries that led to our understanding of it,
and to the impact on society and on history.
Until the end of the nineteenth
century, malaria was thought to be explained by a theory that
you already know, by miasmatism.
In other words,
malaria was a form of bad air. In fact, that’s what the word
means, from the Italian mala, bad,
and aria, air.
So, malaria was bad air that
somehow a susceptible person inhaled,
and it got in his or her body, or was absorbed,
perhaps, through the pores of the skin,
and led, in susceptible people, to this terrible fever.
It was also sometimes called
paludisme, from the word for swamp;
so it was swamp fever. So, the disease then was
absorbed or breathed in, in some way.
In fact, malaria isn’t one
disease. It’s a family of four different
diseases, caused by a parasite, with an extremely complex
lifecycle. The parasite is known as a
plasmodium, and there are four species of plasmodium that cause
human malaria. And I have them on your handout.
falciparum, Plasmodium vivax,
Plasmodium malariae, and Plasmodium ovale.
For the purposes here,
the first two, Plasmodium falciparum
and Plasmodium vivax, are the most important,
medically and historically, and the ones we’ll be talking
about mostly. Now, the plasmodia differ
fundamentally from the other microbial pathogens we’ve
examined so far in the course– bacteria, for example,
and viruses– in that they’re much more
complex life forms, with complex lifecycles that we
need to unravel. Plasmodia were discovered in
1884 by Alphonse Laveran–there he is–a French Army doctor
working in Algeria. It turns out that the plasmodia
don’t exist free in the environment at any stage of
their lives. Instead, they’re adapted to
live either in the body of human beings, or in the gut of certain
species of mosquitoes. And–there we are–this is an
anopheles mosquito doing its thing;
that is to say, having a blood meal,
which is the way that malaria is transmitted from person to
person. The plasmodia–this is again,
in a more schematic way, it gets the point across about
the relationship of human beings and the mosquito.
Plasmodia migrate in the body
of the insect to the salivary glands in the biting apparatus.
So, a biting mosquito,
like this one, is in effect an extremely
efficient vector. It’s sometimes referred to as a
flying syringe, because what it does,
the mosquito does, is to inoculate the plasmodia
directly into the bloodstream of the host.
At this stage the
parasite–we’ll move to look at what happens next.
The first thing we have is the
mosquito taking a blood meal and inoculating the plasmodia
directly into the bloodstream of the unfortunate victim.
At that stage–and here we’ll
see one of the points about the plasmodia,
is that it undergoes a series of morphological changes in
becoming distinct stages in its life,
both in the human body and in the body of the insect.
Initially when it’s injected,
it’s known as a sporazoite, and what it does next is it
migrates, after just a few hours after
inoculation– say you were bitten right now,
within a few hours the plasmodia in your bloodstream
would have migrated to your liver.
And this begins the incubation
period in which the plasmodium reproduces–that is,
asexually–in the liver. And you see its reproduction.
And then after just a number of
days or weeks, it’s released again now in a
new phase, this time known as a merozoite, into the bloodstream.
So, it returns at that point to
the bloodstream. One of the points of the
migration to the liver is that when it’s in the liver,
it’s safely beyond the detection of the human immune
system, and so it reproduces safely in
the liver and then emerges, much more numerous,
into the bloodstream in a new phase in its lifecycle.
At this point in the
bloodstream what happens is that the merozoites–
that’s what they’re now called, the new name of the parasite
for that phase– it enters into–it attaches
itself to and enters into red blood cells or erythrocytes.
Once safely inside the red
blood cell– again it’s not detected by the
immune system– it reproduces asexually–and
you can see it doing so– until at a certain point it has
destroyed the red blood cell and ruptures the red blood cell,
and the parasites return once again to the bloodstream.
I have–this is a picture.
These are of the–by electron
microscope– of the actual rupturing of red
blood cells, and the emergence,
once gain, of the parasites that have just reproduced,
returning to the open bloodstream.
At that point,
the much more numerous merozoites keep repeating this
process of invading red cells, reproducing,
destroying the red blood cells, and then bursting them at
periodic intervals. The interval of time that it
takes is determined by the species of plasmodium.
falciparum and vivax, it’s every forty-eight hours.
And so for Plasmodium
malariae, it’s every seventy-two.
among the brood of merozoites– that is, let’s see,
again–after it’s gone through a number of cycles,
they produce among their offspring what are called–
it’s a new morphologically different stage in the
lifecycle, and that is gametocytes,
that are male and female; and these are in the open
bloodstream. And then the next anopheline
mosquito that takes a blood meal,
as it does so it sucks up the male and female gametocytes that
reproduce sexually this time– we see them here–in the gut,
in the body of the female mosquito,
and then that begins the phase of life in the body of the
mosquito where once again we find it reproduces;
and eventually it leads to the production of sporozoites that
migrate, once again, to the biting apparatus,
the salivary glands of the mosquito.
The mosquito again takes an
infective bite and then– in its next blood meal–and the
whole cycle, this complex cycle of both
asexual reproduction in the body of man,
and sexual reproduction in the body of the mosquito,
the cycle is then complete. Now, let’s return for a second
to the plasmodia and to the insect.
And let me just deal with the
fact that in order– the reason that the female–and
it’s only female anophelines that take blood meals on human
beings– and the reason that the female
anopheline does that is that it needs blood in order to mature
its eggs and to lay them. Having taken a blood meal,
she’s able to mature her eggs, and at that point lays them in
water, and they pass through the cycle
of larvae, pupae, and then the adult
mosquito known as an imago. Now, what happens at that point?
It takes about a week for the
eggs to develop as larvae, pupae and then adult
mosquitoes, and then the mosquito is ready to take flight
and to visit you and me. From the breeding site to the
blood meal, the anopheles mosquitoes have delicate wings
and are normally weak flyers. So, normally she flies about no
more than three kilometers or so, from her birthplace.
Most species of anopheles avoid
sunlight, that dries up their wings, and they avoid strong
winds. But as they take flight,
they’re able to orient themselves to places of human
Because on their antennae there
are sensors that are highly stimulated by carbon dioxide in
the air. And, so, this–the carbon
dioxide plume arising from human settlements and human bodies,
enables the mosquitoes to be attracted to them.
Having arrived at closer range,
the mosquitoes then detect, with other sensors,
odors emanating from sweat. They’re also attracted by light.
And then at close range they
finally use their vision to settle on the site of the body
most suitable for their feast. And human beings cooperate in
this enterprise in that anopheline mosquitoes feast
between dusk and dawn, and they thereby attack
sleeping bodies, lying mostly motionless.
Now, when you hear the buzz of
the harmless culex mosquito that buzzes noisily around you and
attracts your attention, you can be happy,
because most anophelines that transmit malaria are silent and
therefore don’t disturb their hosts.
You’re probably wondering,
how is it that transmission is maintained if the vast majority
of mosquitoes don’t transmit malaria?
Only the females of certain
species of anophelines– and I’ve included two on your
handout as being most important to us: Anopheles gambiae,
which would be my candidate for the most deadly insect for human
beings on our planet, and Anopheles
labranchiae, which was one of the most
important vectors of malaria in Europe and in parts of Africa.
You’re probably wondering if a
female anopheline mosquito lives on average just a few weeks,
and needs to be infected herself before transmitting the
disease, how can transmission be
maintained? Well, there’s a couple of facts
that we need to remember. First, is the vast numbers of
mosquitoes involved in areas where malaria is endemic.
In most areas of high
endemicity, no more than two percent or so of female
mosquitoes are infected at any given time.
But on average,
a human being can be bitten thousands of time in a year.
And it’s also true that an
insect like Anopheles gambiae is famished and
doesn’t feed a single time, but having entered a place of
human settlement feasts repeatedly,
moving from one body to another, thereby ensuring that
in crowded conditions one malarial patient is a major
source of danger to all of those around him or her.
Well, that’s the story from the
standpoint of the mosquito. What happens to the human
victim? What are the symptoms of
malaria? How does the disease have its
impact on the human body? After the incubation period,
symptoms begin when the plasmodia have achieved a
critical threshold number in the bloodstream.
It’s then that the classical
symptoms of malaria begin, with their onset.
Now, let’s remember–return to
our diagram. This process of reproduction,
of entering– that is to say the parasite
enters the blood cell, reproduces, bursts the blood
cell and returns to the bloodstream–
occurs simultaneously for an entire brood throughout the
bloodstream. In other words,
this is happening at the same time throughout the body.
And it’s when there are
sufficient numbers of the parasite in the open bloodstream
that the immune system of the body can detect the parasite,
and it’s then that symptoms begin.
The term for malaria also–it
has many names, this disease.
It was often called
intermittent fever. This process of synchronicity
was known as Golgi’s law, after the malariologist Camillo
Golgi, who discovered it; and he talked about the
different timings of fever. Tertian fever,
that is to say, every forty-eight hours;
or Quartan fever, every seventy-two hours;
or Quotidian fever. You can also have a bout of
intense fever every twenty-four hours,
and that means that you have more than one species of
plasmodium in your bloodstream. You don’t have to choose just
one, you can have several species and several types in
your bloodstream at once. If that occurs,
you can have fever, intermittent fever,
every twenty-four hours. The recurring classic symptoms
then are this intermittent fever, recurring at regular
intervals, like a train schedule.
You have recurring paroxysms of
high temperature, plus chills,
profuse sweating, headache,
general malaise, exhaustion, and with it often
nausea, vomiting and diarrhea.
The precise symptoms depend on
the species of plasmodium, and the most virulent is
Plasmodium falciparum, which causes the most frequent
life-threatening complications, and Plasmodium malariae
and ovale are the most mild.
You see that by entering the
red and attacking red blood cells, the parasite initiates a
cascade of consequences. The red cells can become
misshapen, and they adhere to one another
in clumps, thereby causing blockages in
blood cells- blood vessels, that can be rapidly fatal,
depending on the organ that’s affected.
A frequent cause of mortality
is cerebral malaria, in which there are blockages in
the brain. But the heart can also be
affected, or the gastrointestinal system;
and if malaria attacks the gastrointestinal in particular,
it mimics the symptoms of Asiatic cholera.
Destruction of the red blood
cells also is a cause of profound anemia.
Another important symptom of
the disease is– and this is a child who’s a
malaria patient, and what you see is a painful
and pronounced swelling of the spleen.
This is one of the classic
signs of malarial infection. As I’ve said,
also malaria is terrible in its effects on pregnant women,
leading to hemorrhaging and miscarriage,
and also to congenital malaria with infants born with the
disease. Malaria also is a disease
that’s a major immunosuppressive disease.
It suppresses the immune system
of the body, and therefore gives rise to complications,
especially respiratory diseases;
as I mentioned earlier, pneumonia, influenza and
tuberculosis. So, we should say that the
tuberculosis emergency in the present day, and the malaria
emergency, are inter-locking and inter-related;
malaria provides the substratum for rampaging re-emerging
tuberculosis. I also said that recurring
bouts of malaria lead to neurological damage,
and in the worst cases to a state known as cachexia,
in which a person is indifferent to his or her
surroundings; is unable to learn to be
productive, to take part in civil society.
Another feature of malaria is
that it can lead to relapses; that is, with Plasmodium
vivax. You remember that after the
plasmodium is injected into the bloodstream, it migrates to the
liver. Well in Plasmodium
vivax, the parasite does emerge, but not all of the
parasites. They continue to nestle in the
liver, and they’re beyond the detection of the immune system.
And they can then–even after
the patient thinks that he or she has recovered,
there can be a relapse when the plasmodia,
the parasites, re-emerge from the liver into
the bloodstream. This can be months later,
or even years later, after the initial infection.
once you’ve had lots of bouts of malaria, and you survive,
you develop a partial immunity, an acquired immunity.
But it is short-term,
and it’s also at considerable cost in terms of neurological
damage to the body. Well, the impact on society,
as you can imagine, is severe;
and we’ll be talking about that next time.
But it leads,
this disease–the symptoms, listing the symptoms,
helps us to understand that someone like this as an adult,
who’s anemic, who has perhaps respiratory
diseases, moves painfully and slowly,
and is therefore not a productive worker in agriculture
or in industry. So, malaria leads to backward
systems of cultivation, low productivity,
and lack of investment in agriculture.
It leads to the desertion of
whole- of some of the most fertile areas,
land, because it’s particularly dangerous, and known to be so.
It leads then to poverty,
to illiteracy. Indeed, malaria and poverty are
mutually reinforcing in a kind of vicious downward spiral.
Poverty makes people vulnerable
to the disease. Poverty, that is,
makes people vulnerable because it causes them to live in poor
housing, overcrowded housing; housing that’s porous and
vulnerable to flying insects. It also leads them to
occupational hazards in having to work in areas where the
disease is prevalent. It leads to poor diet,
which makes people more vulnerable;
to inadequate clothing, which makes them more
vulnerable to biting insects. But malaria,
in turn, then leads to further poverty.
The burden of looking after the
ill, that falls on families and communities;
low productivity; low wages;
limited education. This was what Ross meant when
he says, “Those malaria doesn’t kill,
it enslaves.” Well, when was the mosquito
theory of transmission unraveled, and how so?
The idea that mosquitoes were
involved in this disease wasn’t at all obvious.
It wasn’t obvious because,
well, first of all scientists and physicians knew that there
are lots of places where there are gazillions of mosquitoes and
no malaria. It was also clear that
mosquitoes–there was no clear correlation between being bitten
by mosquitoes and developing the disease.
And so the dominant theory in
the nineteenth century was of miasmatism as the cause of the
disease. The unraveling of the
disease–you’ll remember this man, Patrick Manson,
the father of tropical medicine.
He was also one of the figures
who was most closely associated in the development of tropical
medicine, and of the mosquito theory of
transmission, which he discovered for a
different disease called filaria.
And then he had the idea that
perhaps if filaria could be transmitted by mosquitoes,
possibly malaria could as well. And so he joined forces–he
worked, Manson, in London.
This is Ronald Ross,
who was a British military physician working in India.
Now, India was a tremendously
important place in terms of malaria.
Let me just–there was a book
that you might be interested in, and that I would recommend to
those of you who are, which is the correspondence
between Ronald Ross and Patrick Manson,
that led them to the discovery of the mosquito theory of
transmission. Now Ross worked in India,
and he noted that malaria, amongst the general population
of India in the 1890s, led to 5,000,000 deaths.
And he said that it was the
greatest problem of public health in India.
“I think on the
whole,” he wrote, “that the Indian
population of 400,000,000, it causes directly or
indirectly 10,000 deaths a day. And apart from this amount of
sickness, malaria is, of all diseases,
the most important in political,
agricultural and military affairs,”
he wrote, “since it renders large
tracts of fertile land uninhabitable,
impedes cultivation, planting and public works,
and is the most fierce, vicious enemy that armies in
the field have to contend against.
On the whole I think we’re
justified in claiming that the malaria question is as important
as famine or bubonic plague.”
In India, what Ross and Manson
did was to discover–let’s go back to our picture of the
lifecycle of malaria. They traced–through
microscopy, were able to detect in the body of the mosquito
after it had bitten, and they did experiments in
which they– among not human beings but
birds–and they discovered that it was possible to detect the
plasmodia responsible for avian malaria,
under the microscope, in the body of the mosquito.
That was a first major insight,
that the mosquito was in some way implicated.
But then they went further and
they followed the process by which it changed various phases
in the body of the insect and reproduced,
and they traced the migration of the parasite to the biting
apparatus of the mosquito. And then they were able to take
healthy birds and have mosquitoes,
who were known to be infected, feast on them,
and to produce malaria experimentally on birds.
And, so, in 1898,
if you were reading this correspondence,
there’s a eureka moment in which Ross announces that he’s
discovered the mosquito theory of transmission,
and proved it. And he claims that he feels
like Captain Cook, the explorer,
or possibly like Napoleon. And he was not,
however, a naturalist, and he didn’t know about the
speciation of mosquitoes, and the mosquitoes he
described, he described as dappled,
brindled or light brown. He didn’t know about the
species of Anopheles mosquitoes.
It’s at this point that we
should mention then a second major figure–
oops, anyway we’ll see–it doesn’t matter–
Giovanni Battista Grassi, who was the next figure
in the development of the mosquito theory of transmission,
and he does so for human beings. And what he does is he
discovers that it’s possible– in a place called Capaccio he
takes railroad workers, in the midst of a major malaria
outbreak in the summer, and he introduces one variable
in their lives, from a control group of
railroad workers and the surrounding peasantry;
and that is that one group he has living from dusk until dawn
in well-screened houses; and this difference protecting
them from the one factor, which is from the bites of
mosquitoes, prevents their being contracting malaria.
This was one place in which he
did that. And then he also did a
different experiment, which was to use quinine,
which kills malaria parasites in the open bloodstream.
He gave it prophylactically to
a series of workers, as a control group,
in a place like Ostia, during the summer malaria
season, and found that he could protect them as well from
malaria by establishing a chemical barrier between the
mosquitoes and human beings. And then he took the further
step of actually taking mosquitoes who were known to
have feasted on people ill of malaria,
and took them to a hospital in Rome known as the Santo Spirito
Hospital, where he had a volunteer on the
second floor who was in a room where at night they released
hundreds of intentionally infected mosquitoes,
and a couple of weeks later they had their eureka moment
when he had a spike and a temperature of 104,
and they knew that they had successfully transmitted malaria
by human experimentation to someone who had been healthy
until mosquitoes infected with the disease had been allowed to
feast upon him. So, this then happens between
1898 and 1901. And this then is a powerful
factor in the development of tropical medicine.
But it also leads to programs
to combat malaria. Having discovered the pathogen
responsible to it, the plasmodia,
and the vector, female anopheles mosquitoes,
we see the development of public health programs to
destroy the disease– either by attacking the
plasmodia with chemical therapy, that is, through quinine;
or by killing mosquitoes, that is, vector control–the
idea of possibly being able to eradicate malaria.
And next time what I’d like to
do is to follow the practical application then of the
discoveries we’ve talked about today,
about the life cycle of plasmodia and of anopheline
mosquitoes, and see how that leads to the
development of public health strategies.
And I’d like to talk about how
those strategies are being used in the real world today to
combat this crisis of this dreadful vector-borne disease.