Veterinary Clinical Medicine-I (General and Systemic)

Current concepts of diseases

CURRENT CONCEPTS OF ANIMAL / HUMAN DISEASES

• While many diseases are infectious, research in the twentieth century has revealed other kinds of cause of disease: genetic, nutritional, immunological, metabolic, and cytological. The Hippocratics saw some traits such as being phlegmatic as hereditary, but the first demonstration of the genetic basis of a disease was Archibald Garrod's work on alkaptonuria in 1901. Many other kinds of genetic disorders have been identified, and in recent years genetic engineering has offered the possibility of new kinds of treatment for such disorders.
• Hippocrates placed great emphasis on diet as a factor on disease, and the value of citrus fruits in preventing scurvy was established in 1747, but identification of vitamin C as a nutritional requisite of health occurred only in 1932. Diseases caused by nutritional deficiencies can easily be treated by providing the missing vitamins or other nutrient.
• Knowledge of the immune system advanced rapidly in the 1950s, making possible the understanding of diseases that arise from attacks by the immune system on the body's own organs, as occurs in diseases such as lupus erythematosus.
• Metabolic disorders such as diabetes have become increasingly understood as knowledge increases of the physiology of organs such as the pancreas, but causality in such cases is complex, involving an interaction of hereditary and environmental factors.
• Similarly, although knowledge is developing rapidly concerning the nature of the cells and genes involved in the growth of cancers, the causal interactions are enormously complex and hard to identify.
• Currently the authoritative Textbooks of Medicine are divided into parts that implicitly classify diseases in two complementary respects: organ systems and pathogenesis. Most of these are organized around physiological systems, such as the cardiovascular and respiratory systems. But there are also parts that group diseases in terms of pathogenetic mechanisms that can affect various organ systems: oncology, metabolic diseases, nutritional diseases, infectious diseases, and so on. Some diseases are naturally discussed in more than one part, as when myocarditis occurs both under cardiovascular diseases and infectious diseases. Modern medical classification thus blends two overlapping taxonomies of disease.
  • Cardiovascular diseases
  • Respiratory diseases
  • Renal diseases
  • Gastrointestinal diseases
  • Diseases of the liver, gall bladder, and bile ducts
  • Hematologic diseases
  • Oncology
  • Metabolic diseases
  • Nutritional diseases
  • Endocrine and reproductive diseases
  • Diseases of the bone and bone mineral metabolism
  • Diseases of the immune system
  • Musculoskeletal and connective tissue diseases
  • Infectious diseases
  • HIV and associate disorders
  • Diseases caused by protozoa and metazoa
  • Neurology
  • Eye diseases
  • Skin diseases
• The shift from the humoral to the germ theory of disease required a conceptual revolution: the old conceptual and explanatory system was replaced by a radically different one. In contrast, the development in the twentieth century of concepts of genetic, nutritional, immunological, and metabolic diseases were relatively conservative extensions of the nineteenth century ideas: new causes were introduced without denying that the germ theory was right about the causes of diseases to which it had been applied.