Diphtheria

Overview

Diphtheria is an acute, highly contagious bacterial infection caused by the bacterium Corynebacterium diphtheriae. The disease primarily affects the mucous membranes of the respiratory tract but can also affect the skin. Diphtheria is characterized by the formation of a pseudomembrane in the throat, which can lead to severe respiratory obstruction. The disease is transmitted through respiratory droplets from coughing or sneezing and can also spread through direct contact with infected skin lesions.

Etiology and Pathogenesis

Corynebacterium diphtheriae is a Gram-positive, non-motile, rod-shaped bacterium. The pathogenicity of C. diphtheriae is primarily due to the production of diphtheria toxin, an exotoxin that inhibits protein synthesis in host cells. The toxin is encoded by the tox gene, which is carried by a lysogenic bacteriophage. The toxin's mechanism of action involves ADP-ribosylation of elongation factor-2 (EF-2), leading to cell death.

Clinical Manifestations

Respiratory Diphtheria

Respiratory diphtheria typically presents with a sore throat, low-grade fever, and the development of a thick, gray pseudomembrane on the tonsils, pharynx, or nasal cavity. This pseudomembrane can cause significant airway obstruction, leading to difficulty breathing, stridor, and potentially life-threatening respiratory distress. Other symptoms may include malaise, dysphagia, and hoarseness.

Cutaneous Diphtheria

Cutaneous diphtheria manifests as non-healing ulcers covered by a grayish membrane. These skin lesions are typically found on exposed parts of the body and are more common in tropical regions and among individuals with poor hygiene.

Diagnosis

The diagnosis of diphtheria is primarily clinical, supported by laboratory confirmation. Throat swabs or swabs from skin lesions are cultured on selective media such as Loeffler's medium or Tinsdale agar. The presence of C. diphtheriae is confirmed by biochemical tests and toxin production is verified using the Elek test or polymerase chain reaction (PCR) for the tox gene.

Treatment

The treatment of diphtheria involves the administration of diphtheria antitoxin to neutralize the circulating toxin and antibiotics to eradicate the bacteria. The antitoxin is derived from horse serum and should be administered as soon as possible after clinical diagnosis. Antibiotics such as penicillin or erythromycin are used to eliminate the bacterial infection. Supportive care, including airway management and treatment of complications, is also crucial.

Complications

Complications of diphtheria can be severe and include myocarditis, neuritis, and renal failure. Myocarditis can lead to arrhythmias and heart failure, while neuritis can result in peripheral neuropathy and paralysis. Early recognition and treatment are essential to minimize these complications.

Prevention

Diphtheria is preventable through vaccination. The diphtheria-tetanus-pertussis (DTP) vaccine is part of routine childhood immunization schedules. Booster doses are recommended for adults to maintain immunity. In addition to vaccination, public health measures such as prompt identification and treatment of cases, contact tracing, and prophylactic antibiotics for close contacts are essential to control outbreaks.

Epidemiology

Diphtheria was once a major cause of morbidity and mortality worldwide, but widespread vaccination has significantly reduced its incidence. However, the disease remains endemic in some regions, particularly in areas with low vaccination coverage. Outbreaks can occur in settings of poor sanitation, overcrowding, and disrupted healthcare systems.

Historical Perspective

Diphtheria has been recognized since ancient times, with descriptions of the disease dating back to Hippocrates. The development of the diphtheria antitoxin in the late 19th century and the introduction of widespread vaccination in the mid-20th century were pivotal in reducing the burden of the disease. The Schick test, developed in the early 20th century, was used to determine susceptibility to diphtheria before the advent of routine vaccination.

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