Corynebacterium diphtheriae is the pathogenic Gram-positive bacterium that causes diphtheria. Four subspecies are recognized: C. d. mitis, C. d. intermedius, C. d. gravis, and C. d. belfanti. All may be toxigenic.
Although the geographic occurrence for the disease is worldwide, it is mainly to be found in tropical regions and underdeveloped countries. Those facing the greatest risk of contracting the disease are immunocompromised individuals, poorly immunized adults, and unvaccinated children.
When an individual contracts diphtheria, the only affected region of the body is the upper respiratory system. Diphtheria can cause a thick gray coating to build up in the throat or nose making it difficult to breathe and swallow. Once individual contracts the disease, they are contagious for two weeks to a month.
If untreated, the diphtheria toxin can get into the bloodstream causing damage to the kidneys, nerves, and heart.
Cutaneous diphtheria can be caused by both the toxigenic and the nontoxigenic strains of C. diphtheriae. Cutaneous diphtheria presents as nondescript sores or shallow ulcers on the skin, and is usually mild and treatable. Only 1-2% of cutaneous cases become toxigenic.