Diphtheria is an infectious disease caused by the bacterium Corynebacterium diphtheriae. This disease primarily affects the mucous membranes of the respiratory tract (respiratory diphtheria), although it may also affect the skin (cutaneous diphtheria) and lining tissues in the ear, eye, and the genital areas.
What is the history of diphtheria?
Throughout history, diphtheria was a leading cause of death among children, and it was once referred to as the "strangling angel of children". Through the ages, several epidemics struck Europe, and even the American colonies were affected by an outbreak in the 18th century. Most recently, in the 1990s, large outbreaks of diphtheria occurred in Russia and in the former independent states of the Soviet Union.
The diphtheria bacterium was first identified in the 1880s. In the 1890s, the antitoxin against diphtheria was developed, with the first vaccine being developed in the 1920s. With the development and administration of the diphtheria vaccine, the incidence of diphtheria has decreased significantly.
Though it is still endemic in many parts of the world, respiratory diphtheria has now became a rare disease in the United States (with up to five cases per year). Furthermore, whereas diphtheria primarily affected younger children in the prevaccination era, an increasing proportion of cases today occur in unvaccinated or inadequately immunized adolescents and adults.
The symptoms and signs of respiratory diphtheria may initially be similar to a viralupper respiratory infection, however, the symptoms become more severe with the progression of the disease.
Generally speaking, individuals exposed to diphtheria begin to experience symptoms between two to five days after the initial infection, though some individuals may not experience any symptoms at all (asymptomatic).
The symptoms and signs of respiratory diphtheria may include the following:
- Sore throat.
- Difficulty swallowing.
- Nasal discharge (that may contain pus or blood-tinged fluid).
- Enlarged lymph nodes in the neck and neck swelling (producing a "bull neck" appearance).
- Difficulty breathing.
As respiratory diphtheria progresses, individuals may develop the classic adherent thick, gray membrane (pseudomembrane) forming over the lining tissue of the tonsils, pharynx and/or nasal cavity.
Extension of this pseudomembrane into the larynx and trachea can lead to obstruction of the airway with subsequent suffocation and death. See reference two for pictures of the bacteria and the pseudomembrane.
The systemic manifestations of diphtheria are caused by the effects of the diphtheria toxin and its subsequent dissemination to other organs away from the initial area of infection.
Commonly affected organs include the heart and nervous system, leading to complications such as inflammation of the heart (myocarditis), cardiac rhythm and conduction disturbances, muscle weakness, numbness (nerve), and vision changes.
Cutaneous diphtheria is characterized by an initially painful red lesion that eventually becomes a non-healing ulcer covered with a gray-brown membrane. This mild localized infection is only rarely associated with systemic complications.
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).
The mainstays of treatment for diphtheria include diphtheria antitoxin, antibiotics, and supportive care. If diphtheria is suspected in a patient, treatment (antibiotics and antitoxin) should be initiated as soon as possible, even before confirmatory diagnostic test results are available, in order to improve the chances of a favorable outcome. Patients with suspected diphtheria should be placed in isolation in order to prevent transmission of the disease to others.
The effective treatment of diphtheria involves the early administration of diphtheria antitoxin, which neutralizes the circulating diphtheria toxin and reduces the progression of the disease. It is not effective against toxin that has already bound to body tissue. Diphtheria antitoxin is derived from horses, and it is only available from the Centers for Disease Control and Prevention (CDC). Individuals who are asymptomatic carriers and those with localized cutaneous diphtheria do not generally require antitoxin but are treated with antibiotics.
Antibiotics are also recommended in the treatment of diphtheria. The prompt administration of either erythromycin or penicillin can eradicate the bacteria and halt the production of further diphtheria toxin. The administration of antibiotics also assists in preventing the transmission of diphtheria to others. Antibiotics are also recommended for asymptomatic carriers of Corynebacterium diphtheriae and to those who come in close contact with individuals suspected or known to have diphtheria.
Supportive measures may also be necessary in the treatment of diphtheria. Airway obstruction from the pseudomembrane may necessitate the insertion of a breathing tube to prevent suffocation and death. Cardiac monitoring is necessary to manage potential cardiac rhythm or conduction disturbances. Consultation with cardiologists, neurologists, pulmonologists, and infectious disease specialists may also be necessary.