Chapter 1: Introduction

Diphtheria, from the Greek word 6t+€kea for skin (Bretonneau, 1826) referring to a membraneous inflammation of the upper respiratory tract characteristic for the disease, is caused by infection with non-sporulating, obligate aerobic, gram-positive bacilli of the genus Corynebacterium (Mortimer, 1994; McGregor, 1995). This group includes the species of C. diphtheriae (with the subspecies gravis, mitis, intermedius and belfanti), C. ulcerans and C. pseudotuberculosis (C. ovis; Saragea et al,, 1979; Clarridge & Spiegel, 1995). C. diphtheriae is the bacterium causing diphtheria in man. However, C. ulcerans, which usually infects horse and cattle, may in rare cases be a pathogen in man, too (Lipsky et al., 1982). A single human case infected by C. pseudotuberculosis has been described (Lopez et al., 1966). Diphtheria is a communicable disease which besides of the local reaction in the respiratory tract caused by the growth of bacilli also manifests itself by systemic effects of a toxin, most notable in the heart and peripheral nerves (Saragea et al., 1979; Mortimer, 1994; Bethel1 et al., 1995; McGregor, 1995). Clinical symptoms include a slight fever, malaise, sore throat and croup (Scotch word meaning to croak; Park & Bolduan, 1908). Death may result from respiratory obstruction by the membrane or myocarditis caused by the toxin. Mainly in the tropics a cutaneous diphtheria with skin lesions can occur as well, which may disseminate and give rise to nasopharyngeal disease (Liebow, 1958; Ayyagari et al., 1977; Humour et al., 1995). Without specific treatment average case fatality rates ranging between 12 and 86 YO have been reported with the highest mortality in children less than 5 years of age (Park & Bolduan, 1908). By transmitting diphtheria to rabbits and pigeons following exposure of their tracheae to pseudo-membraneous material from human cases, Trendelenburg (1 869) showed that the pseudo-membrane was the contagion. LoefJEer (1884) was the first to isolate C. diphtheriae in pure culture. By infecting various species of animals with different isolates grown on blood agar plates containing 25 YO broth he induced the characteristic symptoms of diphtheria in guinea-pigs and rabbits which finally led to their death, whereas mice and rats remained unaffected. Two years later Roux and Yersin (1888) showed that local lesions could be produced in experimental animals by a lethal, heat-labile toxin from sterile filtered cultures of C. diphtheriae. Brieger and Fraenkel (1 890) isolated the toxin from a culture filtrate by precipitation with ammonium sulphate or alcohol and characterized it as a protein. The precipitate gave rise to necrosis and paralysis of rabbits and guinea-pigs, but did not induce the formation of a pseudo-membrane. They suggested this to depend on the growth of the bacillus. The same year Behring (1 890) immunized guinea-pigs with a culture of C. diphtheriae treated with IC13. In 1913 the first experiments on active immunization of children with a balanced mixture of toxin and horse anti-diphtheria toxin were reported (Behring, 1913). Such a procedure was introduced in North America and used routinely for a number of years. Because the heterologous serum in the vaccination mixture sensitized a considerable proportion of the injected children (Harrison, 1932), the immunization mixture was replaced with vaccines based on toxin detoxified with formaldehyde (Ramon, 1928).