1. CLASSIFICATION OF INFECTIOUS DISEASES. INFECTION PROCESS AND INFECTIOUS DISEASE
Medical research and practice require a systematic approach; therefore, there is a need for classification of infectious diseases. The most successful classification was proposed by Lev Gromashevsky in 1947; he based his classification on the pathogen transmission mechanism and location of the infection process corresponding to such a mechanism in the human body. It is still relevant in the epidemiology, but it is considered as inadequate for infectiologists as many infectious diseases have different transmission mechanisms (plague, tularemia, herpetic infections, etc.), and a pathogen transmission mechanism does not always correspond to its location in the body (for example, brucellosis is classified as an intestinal infectious disease, although it does not affect the digestive system, etc.). The classification of infectious diseases should be based on the principle reflecting some essential features of these diseases. Their key feature is a specific nature of the pathogen, for this reason a classification based on the etiological principle, which does not reject epidemiologic criteria (pathogenic source, transmission mechanism), seems to be the most acceptable. Such classification is scientifically justified, and the common pathogenesis of infectious diseases, aroused by biologically close agents, has practical significance as the etiological factor identifies the principles of infectious disease diagnosis and treatment.
2. ETIOLOGIC CLASSIFICATION
► Bacterioses, including chlamydia infections, mycoplasmoses, and rickettsioses.
► Viral infections.
► Prion diseases.
► Protozoan disease.
► Mycoses.
► Helminthiases.
The diseases inside each group are also divided into anthroponoses, i.e. infectious diseases that make a human being a reservoir and a source of infection, zoonoses, i.e. infectious diseases that make animals a reservoir and a source of infection, but that are also transmissible to humans; sapronoses, i.e. infectious diseases that make abiotic (non-living) environment (soil, water) a reservoir of pathogens. Depending on the pathogen transmission, mechanism of infectious diseases can be divided into the following types: