Diphtheriae is an acute, toxin-mediated disease caused by the bacterium C. diphtheria.

The name of the disease is derived from the Greek diphtheria, meaning ”leather hide”, because of the leathery layer that grows on the tonsils, throat, and nasal passage.

Taxonomy
Family: Corynebacteriaceae
- C. diphtheria biotype gravis
- C. diphtheria biotype mitis
- C. diphtheria biotype belfanti
- C. diphtheria biotype intermedius (lipophyl)

Natural habitats
Human carriers are the reservoir for C. diphteriae and are usually asymptomatic.

C. diphtheria can be isolated from the nasopharynx as well as from skin lesions, which actually represent a reservoir for the spread of diphtheria.

Transmission
Transmission is most often person-to-person contact or contact with items that have the bacteria on them, such as an infected person’s cup or used tissue.

Rarely, transmission may occur from skin lesions.

Clinical significance
C. diphtheria infects the nasopharynx or skin.

Toxigenic strains secrete a potent exotoxin which cause diphtheria.

Toxin production (toxigenicity) occurs only when the bacteria itself infected (lysogenized) by a specific virus (bacteriophage) carrying the genetic information for the toxin (tox gene). Only toxigenic strains can cause severe disease.

The symptoms of diphtheria include pharyngitis, fever, swelling of the neck or area surrounding the skin lesion.

Diphtheritic lesions are covered by an adherent pseudomembrane. (characteristic)

The toxin is distributed to distant organs by the circulatory system and may paralysis and congestive heart failure.

C. diphtheria may also cause cutaneous diphtheria.

Some people with poor hygienic standards (e.g., drugs or alcohol abusers) are prone to colonization on the skin, (more often than in the pharynx ) by C. diphtheria strains, which are often nontoxigenic.

Diphtheria spread easily, but can be prevented through the use of vaccines.

If left untreated, diphtheria can cause severe damage to kidneys, nervous system, heart and can be fatal.