Diphtheria (cont.)

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What causes diphtheria?

Diphtheria is caused by toxin-producing strains of the gram-positive bacillus Corynebacterium diphtheriae. There are four biotypes of the bacterium (gravis, mitis, intermedius, and belfanti), and each differs in the severity of disease it produces. Nontoxigenic strains are usually responsible for less severe diphtheria involving the skin (cutaneous diphtheria).

The signs and symptoms of respiratory diphtheria are caused by the bacterium's ability to cause a localized inflammatory reaction of the cells lining the upper respiratory tract. In certain cases, the disease can become more severe and widespread, and it can involve other organs of the body as well.

How is diphtheria transmitted?

Diphtheria is transmitted to close contacts via airborne respiratory droplets or by direct contact with nasopharyngeal secretions or skin lesions. Rarely, it can be spread by objects contaminated by an infected person. Overcrowding and poor living conditions can further contribute to the spread of diphtheria.

Humans are the only known reservoir of Corynebacterium diphtheriae. Infected individuals may develop symptoms of diphtheria, or they may become carriers of the bacteria with no symptoms (asymptomatic carriers). These asymptomatic carriers can serve as reservoirs for active infection and may transmit the disease to other individuals.

What are the signs and symptoms of diphtheria?

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The symptoms of respiratory diphtheria usually begin between two to five days after exposure to the diphtheria bacterium (the incubation period). Symptoms of respiratory diphtheria may include the following:

  • Sore throat
  • Fever
  • Malaise
  • Hoarseness
  • Foul smelling nasal discharge
  • Headache
  • Cough
  • Difficulty swallowing
  • Difficulty breathing

With the progression of respiratory diphtheria, the infected individual may also develop an adherent gray membrane (pseudomembrane) forming over the lining tissues of the tonsils and/or nasopharynx. This pseudomembrane is necrotic (dead) tissue that develops from the effects of the diphtheria toxin. Individuals with severe disease may also develop neck swelling and enlarged lymph nodes of the neck, leading to a "bull-neck" appearance. Extension of the pseudomembrane into the larynx and trachea can lead to obstruction of the airway with subsequent suffocation and death.

The dissemination of the diphtheria toxin to the rest of the body can also lead to systemic disease, causing complications such as inflammation of the heart (myocarditis) and neurologic problems such as paralysis of the soft palate, vision problems, and muscle weakness.

Cutaneous diphtheria is characterized by a nonhealing skin ulcer covered by a gray-brown membrane. It is typically a localized infection that is rarely associated with systemic complications.

Medically Reviewed by a Doctor on 11/26/2013

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