Immune Response in Human Pathology: Infections Caused by Bacteria, Viruses, Fungi, and Parasites

In the middle of the nineteenth century, it became clear that micro-organisms could cause disease. Effective treatment, however, was not possible at that time; prevention and spread of infectious diseases depended solely on proper hygienic means. At the beginning of the twentieth century, passive and active vaccination procedures were developed against a number of these PATHOGENIC MICRO-ORGANISMS to prevent the diseases in question (rabies, diphtheria, tetanus, etc.). Thanks to the discovery of antimicrobial chemicals (by Paul Ehrlich) and antibiotics (by Sir Alexander Fleming), the threat of infectious diseases seemed to be minimised. Large-scale vaccination programmes against childhood diseases (diphtheria, whooping cough, and polio), started in the early 1950s, raised hopes of finally being able to eradicate these diseases from the planet. This approach was successful for smallpox (1980). However, new infectious diseases have emerged [e.g., Legionella, HUMAN IMMUNODEFICIENCY VIRUS (HIV), Helicobacter, SARS, etc.], and new vaccines and antibiotics are needed. Furthermore, due to intensive medical treatment with antibiotics and immunosuppressive drugs, hospital infections are a growing problem. Bacteria hitherto deemed harmless are causing OPPORTUNISTIC INFECTIONS in immunocompromised patients. The pathogens have developed resistance to many antibiotics, and sometimes no effective antibiotics are available to treat these patients.