BIOLOGY Volume 2 - A Guide to General Biology - 2004

15. HEALTH AND DISEASE

15.1. What are health and disease?

The World Health Organization (WHO) defines health as "a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity." Thus, the term health encompasses three components: physical, mental, and social. Defining what constitutes a disease proves to be considerably more difficult than defining health, since being unwell does not always mean having a disease. For instance, we would readily classify tuberculosis, alcoholic Liver degeneration, and Lung Cancer as diseases, but what about a broken arm? Can a physical injury be considered a disease? In many cases, it is indeed more accurate to speak of an impairment, pathology, anomaly, or disorder rather than a disease. A Classification scheme can help us better understand what should be regarded as a disease.

Classification of Diseases

It is customary to divide diseases into the following six main groups.

1. DISEASES CAUSED BY PATHOGENIC ORGANISMS. Pathogens, or disease-causing organisms, typically include Viruses, Bacteria, Fungi, Protozoa, as well as Flatworms and Roundworms. All of them in one way or another disrupt the normal functioning of the Organism. Diseases caused by bacteria (such as cholera), viruses (such as measles), and fungi (such as ringworm) are referred to as infectious diseases (or simply infections). When the causative agents are protozoa or worms, it is customary to speak of parasitic diseases, or infestations. The most widely known example of such a disease is malaria (caused by a protozoan).

2. "ANTHROPOGENIC" DISEASES. These are also known as social diseases or diseases of civilization. Many of them are particularly characteristic of modern industrial society, such as CORONARY Heart DISEASE, alcoholism, drug addiction, lung cancer, occupational diseases, and pathologies associated with environmental pollution. The latter group includes lead or mercury poisoning, certain cases of asthma, and specific forms of cancer in people living near nuclear power plants.

3. DIETARY DEFICIENCIES. A lack of certain components in the diet leads to severe forms of pathology. A deficiency of such an essential nutrient as protein causes kwashiorkor and marasmus (Ch. 8). The lack of specific Vitamins leads to characteristic avitaminoses, such as pellagra (vitamin B deficiency), scurvy (Vitamin C Deficiency), or Rickets (Vitamin D deficiency). A deficiency of dietary minerals is also hazardous: a lack of Calcium and phosphorus can cause rickets, while iodine deficiency leads to endemic goiter. Dietary deficiency diseases are discussed in Chapter 8.

4. INHERITED AND CONGENITAL PATHOLOGIES. These conditions are causing growing concern among medical professionals and society as a whole. The most well-known Examples of genetic anomalies are cystic fibrosis, Huntington's disease (chorea), and Down syndrome. Along with other pathologies of a genetic nature, these are discussed in Chapter 25. Congenital defects (developmental malformations) are associated with abnormal fetal development, though they are not necessarily genetic in origin. Thanks to advancements in medical science, many children who previously would have died in infancy from such anomalies now survive into adulthood. This places a responsibility on society to ensure a fulfilling life for individuals with sometimes severe mental or physical disabilities. However, The Development of genetic screening increasingly allows hereditary anomalies to be detected at an early Embryonic Stage when Pregnancy can still be terminated. In general, the issue of congenital defects involves many social and ethical aspects, and therefore continues to provoke ongoing debate in society. Some of these details are discussed in Chapters 21 and 25.

5. AGE-RELATED DISEASES. The natural degeneration of Tissues as an organism ages can also lead to anomalies and diseases. For example, the weakening of the eye Muscles in elderly people causes presbyopia, which is very common at this age. Age-related changes in Bones and joints cause Arthritis, while a loss of elasticity in the arterial walls leads to atherosclerosis.

6. MENTAL DISORDERS. This group includes a wide range of anomalies, examples of which are Schizophrenia, senile dementia, and depression. Medications have been developed that can significantly alleviate—to the point of eliminating clinical symptoms—some forms of such disorders. Public attitudes toward the "mentally ill" have also changed dramatically over the past century; instead of forced hospitalization for months or even years, outpatient care and day hospitals are becoming increasingly widespread.

The six groups described above can be combined into two major categories.

1. Infectious (communicable) diseases. This term refers to pathologies that can be transmitted from a diseased organism to healthy ones. All of them belong to Group 1. Pathogens of infections or infestations are spread among people via airborne droplets (through sneezing, coughing, or talking) or through direct contact with an infected person, their feces, or biological fluids (Blood, secretions, semen, etc.), including sexual intercourse, as well as via shared objects, food, and Water. In many cases, the pathogen is transmitted from a sick person to a healthy one by a specific vector. For example, contracting malaria requires being bitten by a mosquito carrying the malaria parasite (Section 15.3.3); bubonic plague is transmitted by fleas, epidemic typhus by lice, and so on.

2. Non-infectious (non-communicable) diseases. These include diseases from groups 2 through 6. A special case is represented by inherited anomalies (Group 4), which parents pass on to their children by transmitting a defective set of genes.

It is difficult to draw a sharp line between different groups of diseases. For instance, many cardiovascular (Group 2) and mental (Group 6) disorders, although not considered genetic (i.e., lacking a clear, well-defined inheritance pattern), require a genetic predisposition to manifest. Disease, much like health, encompasses physical, mental, and social dimensions. For example, tuberculosis or nutritional deficiencies are associated with poverty, while many infectious diseases are linked to poor sanitation—meaning they are rooted in the social conditions in which people live.