Bacterial Tropical Infections

© 2005 The Medicine Publishing Company Ltd 31 MEDICINE 33:7 Diphtheria is caused by superficial infection of the respiratory tract or skin with toxin-producing strains of the bacterium Corynebacterium diphtheriae. The organisms do not actively invade deep tissue or the blood, but multiply locally, producing diphtheria toxin. This results in necrosis of the mucosal cells and production of a thick, grey pseudomembrane containing fibrin, epithelial cells, bacteria and neutrophils. Diffusion of toxin into the circulation causes toxic neurological and myocardial complications. The clinical manifestations and epidemiology of infection with C. diphtheriae vary between parts of the world and over time, depending on host and environmental factors, some of which are not fully understood. The most important factors are individual and population immunity to the diphtheria toxin mediated by neutralizing antibody; this is induced by immunization with formalin-inactivated toxin (toxoid) and/or natural immunizing events resulting from asymptomatic carriage or low-grade infection (often cutaneous).