Humanity’s Fight Against Infectious Diseases

Humanity’s fight against infectious diseases is fairly recent when it comes to widespread or worldwide impact. We only experienced the full benefits recently. This means, instead of centuries dividing our revelations, we can go all the way from identification of a new infection or viral strain to developing drugs and vaccines (in some cases) against it.

The Early Civilizations

Infectious diseases, and our fight against them, has lasted as far back as the earliest civilizations. There were definitely infectious diseases even before this time. However, early civilizations have the two factors needed for widespread impact: gathering places for large groups of people, and traveling for trade. Let’s look at some of the plagues and epidemics early civilizations faced.

Why 300 worked: the plague of the Peloponnesian War (430 BCE)

That’s an exaggeration. But it’s true that conflict and war create conditions ripe for pandemics (affecting a large amount of land and people). Thucydides, who wrote a history of the Peloponnesian War, describes the symptoms from firsthand experience. The plague went up from below Ethiopia in northern Africa through Egypt into Athens, and east into Persia. As the Spartans besieged the Athenian walls, the plague attacked the inside, killing one-third to two-thirds of the population. Until now there is no consensus on the actual cause of the plague.

What the Gladiator missed: the Antonine Plague (165 CE)

The names “Marcus Aurelius” and “Lucius Verus” might be familiar to fans of The Gladiator (2000 dir. Ridley Scott), as central characters in the story (historical accuracy aside). Historically, known as “philosopher-warriors,” they were co-ruling Rome at a time when the Empire’s campaigns were reaching into West Asia. However, in 165 CE, as the Roman soldiers marched back, they brought a disease from West Asia back with them into the heart of Rome. Generally considered to be an early strain of smallpox, it killed up to 10% of the entire Roman Empire (which includes northern Africa and most of Europe). Since it took over 20 years to run its course, scientists believe it was able to mutate quickly and defeat efforts to contain it–eventually infecting and killing both the emperors.

The Cyprian Plague (249 CE)

This plague, named after the bishop of Carthage, was difficult to identify because there was no historian or medical authority who described the symptoms. However, independent sources mentioned a plague, and eventually the symptoms could be identified from the recorded prayers of the bishop. The ever-moving flow of people from Alexandria, Egypt to the Roman Empire and beyond spread the plague until as many as 5,000 were reported dead every day. While the later Justinian Plague is generally considered instrumental in the fall of the Roman Empire, the Cyprian Plague played a part in depleting the military and the tax base in one attack.

The Justinian Plague (541 CE)

This was one of the most destructive plagues, killing 50% of the world’s population in the 6th century over 50 years, as it ran its course in continent after continent. Now recognized as an early strain of the Black Death in the later 1300s, it swept through and beyond all of the Roman Empire, defeating the emperor’s plans to reunite those within it. Reduction in agricultural workers, subsequent famine, lessened military might, and prolonged battles all added to the casualty list.

Leprosy (1000s CE)

Leprosy is one of the oldest documented diseases, carrying with it as much religious stigma as medical. Because of its long-lasting and crippling effects, the pandemic caused mass creation of institutions for containment. These were known as lepers’ hospitals or lazar-houses. There was no recovery from it, and residents were expected to live there the rest of their lives. The institutions created, and the methods used to contain its spread, laid the foundation for the real fight against infectious diseases, starting with the Bubonic Plague in the 1300s.

The Early Fight Against Infectious Diseases

The Chinese empires had some of the earliest steps taken against plagues in terms of containment such as quarantine, and in preventing transmission of the disease through contaminated items. Two hundred years before Europe, they decided to strengthen their own bodies against “invasion,” and pre-infected themselves with certain diseases to avoid contracting a more fatal version. Advances in European medicine helped them understand the presence of microbes and particles that spread disease, later on. Egyptian history also shows that there was some knowledge of how to diagnose and treat a disease. However, it’s the European-slash-Mediterranean journey that directly led to our fight against infectious diseases as we know it today.

The Modern Fight Against Infectious Diseases

There are many ways to narrate the modern fight against infectious diseases. You can read about it by sickness, by cure, by approach, by discovery–and still never run out of material. To simplify, let’s take a look at how our modern response to new diseases eventually developed.  

Quarantine

In the 1100s, 1104 to 1110 CE, the Black Death (plague) is first thought to have hit Europe. At that time, Europe had only just begun building lepers’ hospitals to keep them away from society. The thought of isolating victims of any other kind of disease, to keep it from spreading, had not reached medical or public knowledge. As a result, 90% of the European population was lost to the plague.

In the 1300s, the Black Death (bubonic plague) came back to Europe with a vengeance, through trade ships in the Mediterranean to Italy. While it spread quickly and took many lives, people recognized that contact with infected people and items made it easier for them to contract the same disease. The first attempt to isolate those with the disease came when ports started to deny entry to ships they suspected of coming from places where the disease was already spreading.

They imposed a period of 30 days of isolation, extending it later to 40 (for mainly socio-religious reasons). Forty, quarante, is why it’s called a quarantine. As the plague victims literally piled up, they buried the bodies in mass graves far away from the city, also to contain the disease. Eventually, victims and their caregivers were placed in houses outside the city. The authorities even went so far as to seal up some houses with the plague inside before it could spread.

Those were the first attempts to isolate those with diseases so it would not spread. Today, it is one of the first responses when a new, fast-spreading virus is identified in a geographic location.

Transmission

After the Europeans recognized the need for quarantine and that it actually worked, the next logical step was understanding how a disease spreads.

Girolamo Fracastoro, who lived in the 1450s to the 1550s, was born in Verona, Italy. (Yes, the same setting as Shakespeare’s Romeo and Juliet.) He was working as a physician when the syphilis plague broke out from the 1490s to the 1500s. In fact, his poem called “Syphilis or the Gallic Disease” was what gave that plague its name. All they knew was that it was a sexually transmitted disease, and that sailors were most likely to spread it.

As he studied syphilis and other diseases, Fracastoro was the first to suggest that diseases actually had “seeds” that would grow in a host and affect them, causing the disease. Not only that, like a flowering tree, it would spread seeds to others as well. He proposed three means of disease transmission that are familiar to us: person-to-person transmission, transmission through infected items, and airborne transmission.

While it would take 300 years for his theories to make a difference, it was a crucial turning point in containing and limiting the spread of disease through isolation or destruction of contaminated items.

Differentiation

Even if the medical world was starting to realize that diseases had “seeds,” they were still very much bound by generalizations about diseases. In other words, they treated all diseases alike. It was only in the 1600s to the 1700s that some scientists and researchers realized that different signs and symptoms meant different diseases. If the diseases could be differentiated, they could be individually studied for causes. When causes of disease were learned, it would greatly help in finding cures.

Thomas Sydenham, who was a British practicing physician in the 1600s, is known for a cool head when it came to medical theories. If a fever or sickness could run its course without killing the victim (to his knowledge), he would let it. As a result, his observations on how different kinds of “fever” affected the victims became a basis for differentiating diseases from one another. He was one of those to identify scarlet fever, which tended to cause epidemics.

Giovanni Morgagni, an Italian physician who lived from the late 1600s to 1700s, furthered the understanding of differentiating one disease from another. Despite his closeness to the Roman Catholic Church, Morgagni was intent on discovering more about what science could reveal about sicknesses. His specialty was anatomy, the human body, and his experience showed him firsthand how different diseases affected the body differently.

It may seem straightforward to us today, but at the time, identifying what made one disease different from another was a breakthrough. Theories of how to treat diseases were leaving the speculative and entering the scientific. 

Immunization

In the late 1700s, Edward Jenner realized that those who got the milder, rarely-fatal cowpox were unaffected by the smallpox epidemics that swept back and forth across Europe. To demonstrate his theory, he infected a boy with the cowpox and showed how he became immune to smallpox. It took a while for the idea to catch on, but Europe eventually became fully inoculated with smallpox. This knowledge grew up between the ability to differentiate diseases, and the later full germ theory of infection Louis Pasteur proposed. 

Origin

The medical world now knew that quarantine or isolation would limit the spread of a disease, that there were several kinds of disease transmission, and that different diseases had different effects on the human body. Now it learned something else: the origin of diseases. Even though they discovered how infection “seeds” were transmitted, it was mainly basic theory. They did not yet know what, exactly, was being transmitted.

Although the microscope was invented in the late 1500s, it was only used to isolate causes of infection by the 1800s. Louis Pasteur, a familiar name, first used the microscope to study the origin of microorganisms. He discovered that it was microorganisms in milk that turned it sour over time. If microorganisms in milk would make it unfit to drink, what if microorganisms in human bodies made them sick in the same way?

As the 1900s entered, Robert Koch successfully isolated the bacteria of only one disease, anthrax. After gathering the bacteria from an infected host, he placed the bacteria into healthy mice and proved that they became infected by anthrax. More than that, the bacteria that grew in their infected blood was the same as what was first introduced into their bodies. Koch finally proved that diseases originated with microorganisms that infected human bodies.

They also finally discovered that different strains of bacteria could be related, and that one kind of bacteria could cause more than one disease. While disease strains could evolve and reappear, it would now be faster to identify the attack and how to treat it.

Today’s Fight Against Infectious Diseases

Each generation has experienced an epidemic in one form or another, whether it directly affected them or not. The 1918 Spanish Influenza epidemic following World War I was the startling aftermath of both terrible living conditions and unprecedented travel across the world. The 1980s saw the AIDS epidemic, and more recent ones are SARS, MERS-Cov, the Zika virus, and Ebola. The difference is now, for each new epidemic that appears, we draw on the last 750  years of medical development and replicate it within years, months, or even weeks.

Ed Yong writes in The Atlantic that the most recent global epidemic, Covid-19, is a very 2020 epidemic. By this, he points out that everything needed to contain and cure an epidemic–differentiation, transmission, quarantine, and exploration of cures and prevention–all happened within two months. While the long history of our fight against infectious diseases is full of mistakes and corrections, it equipped us to respond globally to defend ourselves against them.