DIPHTHERIA! KEEP OUT!
As with scarlet fever, diphtheria (Corynebacterium diphtheriae) only becomes the dread disease that was quarantined and feared after it becomes infected with a toxin-producing bacteriophage (bacteria-infecting virus). You can be infected with an uninfected strain of C. diphtheriae and not develop any illness - the disease itself requires both the virus AND bacteria (well, one inside the other, of course).
When C. diphtheriae starts exuding toxins, it’s not surprising that the disease was so frightening. Those toxins enter the cells of the nasopharynx and inhibit protein synthesis, which eventually causes apoptosis (cell death), localized necrosis, and inflammation from the body’s response to the dead and dying cells.
The Strangling Death
The combination of those exotoxins, and the body’s response to the bacteria and affected epithelial cells, creates diphtheria’s strangling effects. Bluish skin, cough, difficult and painful swallowing, and rapid difficult breathing are all a result of the swelling and pseudomembrane formation in the throat.
Despite antitoxins, antibiotics, and incredibly sophisticated intensive care units, this disease still kills nearly 10% of all patients, and 20% of those under five or over forty. Diphtheria can kill either by strangulation or overloading the organs of the body with toxins; when adults die of the disease, toxin overload is more common than strangulation. Even when patients survive, heart damage from myocarditis and lingering pain from peripheral neuropathy can continue to cause problems for months or years.
Textbook of Pediatrics. Julius Parker Sedgwick and Carl Ahrendt Scherer, 1922.