Prevention is much more efficient than treating infectious diseases. Prevention may involve general improvements in sanitation and the nutritional state of the population or more specific maneuvers such as immunization. Toxoids, or altered toxins, are used to immunize against tetanus and diphtheria, two diseases where the major damage is done by the toxin rather than invasion by the microbe. Attenuated, or weakened, live viruses are used to immunize against poliomyelitis and rubella (German measles). Killed organisms or fractions of organisms are the immunizing agents for influenza and typhoid fever. The live virus vaccines usually give longer-lasting protection than killed vaccines. Immunization with a related virus (vaccinia, or cowpox virus) has been effective in eliminating smallpox as a threat to humans.
Patients who may spread highly contagious diseases to other patients may have to be isolated while they are undergoing treatment. Thus, before chemotherapy for tuberculosis was available, patients with this disease were separated from the rest of society in sanitoriums. Now, because therapy is so effective, these patients may be treated in general hospitals or even in their own homes. Infections that may be acquired in a hospital can be eliminated or reduced by strict attention to cleanliness and avoidance of cross-contamination from one patient to another, from patients to hospital personnel, and from personnel to susceptible patients.
THERAPY OF INFECTIOUS DISEASES
Most infections are self-limited and require no therapy. Appropriate therapy, however, is effective in shortening the course of illness, reducing the risk of transmission to other patients, and, in the case of severe infections, reducing mortality. No truly effective agents for the therapy of infection were available until the 1930s, when sulfonamides were developed. These agents interfere with steps in the metabolism of bacteria and are effective therapy for certain bacterial diseases. Penicillin, the first of the antibiotics, became available in the 1940s. Antibiotics are substances produced by microbes that act against other microbes. The useful antibiotics are relatively nontoxic to mammalian systems. Antibiotics have a specific spectrum of action, and thus some agents are more effective for certain infections. Commonly used antibiotics include the penicillins, tetracyclines, cephalosporins, and the aminoglycosides. In addition, several nonantibiotic drugs are effective against bacterial infections. Fungal infections will respond to chemotherapy, and drugs effective against a few viral infections have been developed. The vast majority of viral infections, however, remain unaffected by any known therapeutic agents. New antimicrobials are constantly being developed and tested. This research is important because microbes can develop resistance to established agents.
Although the major infectious scourges of society have been eliminated or reduced, infectious-disease research is still of major importance. Infections continue to afflict millions of people each year and are still a significant cause of discomfort, severe illness, and death. Advances in medical technology help many patients overcome serious disease, but these new treatments also impair the defenses of these patients, leaving them susceptible to other severe infections. Therefore, if advances in cancer therapy and organ transplantation are to continue, better methods of preventing and treating accompanying infections in these patients are vital. Some of the chronic debilitating diseases that have been previously thought to be noninfectious may in fact be related to infectious organisms. Thus, such diverse conditions as diabetes mellitus and multiple sclerosis may be caused by infectious agents. The new science of genetic engineering may enable scientists to alter the properties of microbes so that they can serve as effective immunizing strains without causing disease. In addition, alterations in microbes may result in production of antibiotics that may be more active and less toxic than those previously available. A more complete understanding of normal host defenses allows the manipulation of these mechanisms in an effort to prevent, control, and treat infections.