Short answers, pulled from the story.
Diphtheria is a bacterial infection caused by Corynebacterium diphtheriae. The disease's most dangerous effects are produced not by the bacteria themselves but by an exotoxin they release, which can damage the heart, nerves, and kidneys in addition to forming a lethal membrane in the throat.
Among untreated diphtheria patients, roughly 40-50 percent die. Even with treatment, death occurs in 5-10 percent of diagnosed cases. In children under five and adults over forty, the fatality rate can reach 20 percent.
The first diphtheria vaccine, a toxin-antitoxin mixture called TAT, was developed by William H. Park in 1914. The modern toxoid vaccine - based on an inactivated form of the toxin - was introduced in the 1920s and widely adopted after World War II. Alexander Thomas Glenny improved its effectiveness in 1926 by treating the toxoid with aluminum salts.
Emil von Behring won the first Nobel Prize in medicine in 1901 for his work on diphtheria. He and Shibasaburo Kitasato had demonstrated in 1890 that serum from immunized animals could cure the disease in non-immunized animals, and successful treatment of human patients using horse-derived antitoxin began in 1894.
After the breakup of the Soviet Union in 1991, vaccination rates in the newly independent countries fell sharply. Between 1991 and 1998, as many as 200,000 diphtheria cases were reported across the Commonwealth of Independent States, resulting in 5,000 deaths. In 1994 alone, the Russian Federation recorded 39,703 cases.
The pseudomembrane is a thick, grey coating of dead tissue that forms in the throat within two to three days of diphtheria infection. It can extend from the nose across the tonsils, voice box, and into the lungs, blocking the airway and potentially causing death by strangulation. Pierre Bretonneau named the disease in 1826 after the Greek word for leather, describing exactly this membrane.