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What is Diphtheria? - Definition & History

Instructor: Bridgett Payseur

Bridgett has a PhD in microbiology and immunology and teaches college biology.

Diphtheria is no longer a major concern in the developed world. But what is diphtheria, anyway? And how did scientists and physicians control this disease? Read on to find out!

What is Diphtheria?

You might have read about someone with diphtheria in an old novel. It sounds like an old-fashioned disease, one that no longer causes problems in developed countries due to widespread immunization.

Diphtheria is a communicable, infectious disease caused by the bacteria species Corynebacterium diphtheriae. It is an airborne infection, meaning it's spread from person to person through coughing or sneezing. Diphtheria can also be transmitted by touching a contaminated object, such as a doorknob. Less commonly, diphtheria can be contracted when bacteria infect an open wound.

Diphtheria is primarily a respiratory infection. It can be diagnosed through its trademark pseudomembrane, a gray layer of film that grows in the back of the throat. Other symptoms include fever, sore throat, and overall weakness.

Microscopic image of the bacteria that cause diphtheria infection.
diphtheria bacteria

While diphtheria only grows in the respiratory tract, it can harm organs all over the body. How does it do this? C. diphtheriae bacteria produce a toxin, a protein that can diffuse throughout the body, causing damage. The diphtheria toxin prevents cells from producing proteins, effectively killing them. This can be fatal if important organs, such as the liver or heart, are attacked.

Diphtheria in the Past

While diphtheria is no longer considered a major public health threat, it previously had a bad reputation. In 1921, over 200,000 people in the United States alone were infected with diphtheria.

It might be difficult to determine how long humans have been dealing with diphtheria, as it went by many different names over the years. It wasn't officially given its name of diphtheria until 1826, by a French physician.

In 1883, Swedish scientist Edwin Klebs discovered the bacterium responsible for causing diphtheria. A year later, German scientist Friedrich Loeffler helped provide more evidence proving that C. diphtheriae was indeed the cause of diphtheria. He also discovered the toxin produced by the bacteria.

Diphtheria Antitoxin

There were very few treatments available for diphtheria initially. One treatment involved a tracheotomy, a surgery to create an opening in the airway to allow the person to breathe. Unfortunately, this surgery could not treat the toxin produced by the bacteria, and was not always successful.

In 1890, Shibasaburo Kitasato and Emil von Behring began studying a way to combat the diphtheria toxin itself. They injected heat-treated diphtheria toxin into guinea pigs, who produced antibodies against the toxin. The guinea pigs' serum was then used to treat other animals with diphtheria. The serum is known as diphtheria antitoxin, meaning it fights off the toxin.

Eventually, Kitasato and von Behring realized they would need serum from larger animals to produce enough antitoxin for humans, and began immunizing horses. During the 1890s, antitoxin treatment began significantly reducing the death toll of diphtheria. Von Behring won the first Nobel Prize in medicine in 1901 for his contributions.

Development of the Diphtheria Vaccine

Of course, an ounce of prevention is worth a pound of cure, so von Behring began to look at ways to induce long lasting immunity against diphtheria infection. He combined purified diphtheria toxin and antitoxin, and found that this combination could create immunity, without causing disease. William Park continued toying with this idea, trying to find an ideal balance between the amount of antitoxin and toxin to provide immunity without causing bad side effects.

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