Diphtheria, an infectious disease caused by the bacterium Corynebacterium diphtheria, primarily infects the throat and upper airways and produces a toxin affecting other organs. Here's more on the disease.

The illness has an acute onset and the main characteristics are sore throat, low fever and swollen glands in the neck, and the toxin may, in severe cases, cause myocarditis or peripheral neuropathy. The symptoms of diphtheria usually begin two to seven days after infection. Symptoms of diphtheria include fever of 38°C (100.4°F) or above, chills,fatigue, bluish skin coloration (cyanosis), sore throat, hoarseness,cough, headache, difficulty swallowing, painful swallowing, difficulty breathing, rapid breathing, foul-smelling and bloodstained nasal discharge, andlymphadenopathy.

Within two to three days, diphtheria may destroy healthy tissues in the respiratory system. The dead tissue forms a thick, gray coating that can build up in the throat or nose. This thick gray coating is called a “pseudomembrane.” It can cover tissues in the nose, tonsils, voice box, and throat, making it very hard to breathe and swallow.

Symptoms can also include cardiac arrhythmias, myocarditis, and cranial and peripheral nerve palsies. The diphtheria toxin causes a membrane of dead tissue to build up over the throat and tonsils, making breathing and swallowing difficult. The disease is spread through direct physical contact or from breathing in the aerosolized secretions from coughs or sneezes of infected individuals.
Human-to-human transmission of diphtheria typically occurs through the air when an infected individual coughs or sneezes. Breathing in particles released from the infected individual leads to infection. Contact with any lesions on the skin can also lead to transmission of diphtheria, but this is uncommon.

Indirect infections can occur, as well. If an infected individual touches a surface or object, the bacteria can be left behind and remain viable. Also, some evidence indicates diphtheria has the potential to be zoonotic, but this has yet to be confirmed. Corynebacterium ulcerans has been found in some animals, which would suggest zoonotic potential.

The disease may remain manageable, but in more severe cases,lymph nodes in the neck may swell, and breathing and swallowing are more difficult. People in this stage should seek immediate medical attention, as obstruction in the throat may requireintubation or a tracheotomy. Abnormal cardiac rhythms can occur early in the course of the illness or weeks later, and can lead to heart failure.