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Diphtheria Causes and Risk Factors
Diphtheria is caused by the bacterium Corynebacterium diphtheriae, a gram-positive bacillus. There are three biotypes of the bacterium (gravis, mitis, and intermedius) capable of producing diphtheria, though each biotype varies in the severity of disease it produces. The Corynebacterium diphtheriae bacterium causes disease by invading the tissues lining the throat and producing diphtheria toxin, a substance which destroys the tissue and leads to the development of the adherent pseudomembrane characteristic of respiratory diphtheria. The diphtheria toxin may be absorbed and disseminated via the blood and lymphatic system to other organs distant from the initial infection, leading to more severe systemic sequelae (pathological conditions resulting from a prior disease, injury, or attack). Cutaneous diphtheria is usually caused by non-toxin-producing organisms, thereby typically causing a milder form of the disease.
Diphtheria is transmitted by infected individuals and asymptomatic carriers (individuals who are infected but do not exhibit symptoms). Transmission occurs via inhalation of airborne respiratory secretions or by direct contact with infected nasopharyngeal secretions or skin wounds. Rarely, infection can be spread by contact with objects contaminated by an infected person.
Risk factors for the development of diphtheria include absent or incomplete immunization against diphtheria, overcrowded and/or unsanitary living conditions, a compromised immune system, and travel to areas where the disease is endemic, especially in individuals who have not obtained booster shots (vaccine).
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