INFECTIOUS DISEASES AND TREAMENT

WHEN DISEASE is the result of invasion of the human tissues by bacteria and other micro-organisms, the condition is called an infection. Those infections which are transmitted naturally from one person to another are broadly classed " infectious diseases ". For various reasons, including administrative expediency, a number of these diseases are regarded as the responsibility of special hospitals—the infectious diseases hospitals. Although the classification is arbitrary rather than strictly scientific, it accounts for the selection of diseases included in this chapter. It also explains, why venereal diseases, tuberculosis, parasitic infections and tropical diseases are dealt with elsewhere in this site.
The more we know about the natural history of infections, the more rational is our treatment likely to be ; and we shall be more skilful in protecting our patients against the hazards of complications. Stated briefly, the effects of bacterial invasion are determined principally by the virulence of the micro­organism and the efficiency of the defense mechanism of the host. There is a very wide range of possibilities: infection may occur without perceptible illness; and at the other end of the scale the infection may overwhelm the body defenses and cause death in a few hours.
An acute infection may thus be regarded as a struggle between a susceptible host and a pathogenic organism. To achieve success, whether in prevention or treatment, it is necessary to realize that measures which enhance the recuperative capacity of the host are no less important than those which diminish the attacking power of the micro-organism. The febrile period is so short—following effective chemotherapy—that the value of general nursing management is easily overlooked ; but there is no doubt of its importance in severe infection with constitutional upset.
At the outset, it is worth while to draw attention to an important contrast between bacterial and viral infections. In almost all bacterial infections the organism remains mainly extracellular and can thus be reached with comparative ease by substances which are present in the blood stream. Although it is reasonable to assume that there is a temporary stage of virasmia in many of the virus diseases, the causative organism is capable of growth only inside the cell so that it rapidly becomes inaccessible to the usual methods of treatment. Such localization of the virus in body cells has often occurred by the time the infection becomes manifest, and up to the present no practicable method has been devised of modifying the effect after the cell has been invaded. The . specific treatment of nearly all virus diseases therefore still remains beyond our reach. Cellular damage by a virus may be followed by secondary bacterial infection. This complication may call for the use of specific therapy; and such treatment is often used preventively—in anticipation of bacterial invasion.