DIPHTHERIA

acute infectious disease caused by the bacillus Corynebacterium diphtheriae and characterized by a primary lesion, usually in the upper respiratory tract, and more generalized symptoms resulting from the spread of bacterial toxin throughout the body. Diphtheria was a serious contagious disease throughout much of the world until the 20th century, when its incidence in Europe and North America was greatly reduced by immunization measures. It still occurs mainly in the temperate regions of the world, being more common during the colder months of the year and most often affecting children under the age of 10. The diphtheria bacillus was discovered and identified in Germany by Edwin Klebs (1883) and Friedrich Lffler (1884). In most cases the bacillus is transmitted in droplets of respiratory secretions expelled by active cases or carriers during speaking or coughing. The most common portals of entry of the diphtheria bacillus are the tonsils, nose, and throat; the bacillus usually remains and propagates in that region, but the toxin that it produces is disseminated throughout the body by way of the blood and lymph vessels. This toxin, called diphtheria exotoxin, is responsible for most of the symptoms of the disease. The symptoms of diphtheria include moderate fever, a tired feeling, chills, and a mild sore throat. The propagation of the diphtheria bacilli leads to the formation of a thick, leathery, grayish membrane that is composed of bacteria, dead cells from the mucous membranes, and fibrin (the fibrous protein associated with blood clotting). This primary lesion firmly adheres to the underlying tissues of the mouth, tonsils, pharynx, or other site of localization. The more remote lesions caused by the circulating toxin primarily affect the heart muscle and peripheral nerve tissue; in more severe cases the resulting heart failure and paralysis may lead to death. There are several types of diphtheria, depending in large part on the anatomic location of the primary lesion. They include the following: (1) Anterior nasal diphtheria, in which the membrane appears inside the nostrils. Almost no toxin is absorbed from this site, so there is no danger to life and complications are rare. (2) Faucial, or tonsillar, diphtheria, the most common type, in which the infection is limited mostly to the tonsillar region. Most patients recover if properly treated with diphtheria antitoxin. (3) Nasopharyngeal diphtheria, the most often fatal form, in which the tonsillar infection spreads to the nose and throat structures, sometimes completely covering them with the membrane and causing toxemia (blood poisoning). (4) Laryngeal diphtheria, usually resulting from the spread of the infection downward from the nasopharynx to the larynx; the airway may become blocked, and must be restored by inserting a tube or cutting an opening in the trachea. (5) Extra-respiratory diphtheria, consisting of those forms of the infection that affect parts of the body other than the respiratory tract, notably the skin, following a wound or sore. In response to the presence of diphtheria exotoxin, the body makes a neutralizing substance called antitoxin, which enables the affected person to recover from the disease if produced fast enough and in sufficient quantities. The only effective treatment of diphtheria is in fact the prompt administration of this antitoxin, which is obtained from the blood of horses that have been injected with exotoxin and have responded by producing antitoxin. Besides neutralizing exotoxin in the bloodstream, the antitoxin also confers a relatively long-lasting immunity on the patient. Active protection against diphtheria has become a routine measure in many countries through immunization with diphtheria toxoid, a form of the exotoxin that has been rendered nontoxic but that has retained its capacity to induce antitoxin formation once injected into the body. The diphtheria toxoid is usually first given during the first few months of life, with booster doses within one or two years and again within five or six years of age.