Causation of Diseases

CAUSATION OF DISEASES

Introduction  

Health and diseases have always been matters of concern of the society. This resulted in constant search for improvement in the quality of living and maintenance of a healthy society. In that process various concepts on health, diseases and treatment emerged, thereby the practice of medicine got refined on scientific basis. The emergence of biomedicine with the advent of Germ theory completely changed the outlook towards health and diseases and efforts in scientific investigation started finding correlation with material cause to every diseases. Though this helped in rational explanation to certain group of diseases, it opened up more questions on causation of several other diseases.  In spite of development in more theories and concepts, there is a consensus that health and well-being does not simply mean the absence of pain and suffering or the lack of disease, disability, defect and death, but has a positive dimension. This call for holistic approach in health care.

Understanding the cause of disease is the key to begin the process of finding remedies that could cure them. Every medical system has its own models of identifying the reason of diseases. Based on those concepts they develop models of treatment. The biomedicine uses the knowledge of pathogens as the root cause of the infectious diseases and therefore, uses antibiotics and anti viral therapies to overcome such diseases. Based on the theory of Tridosha, Ayuveda explore treatment to bring harmony of the doshas. Homeopathy considers all chronic diseases due to miasms.  Though all these models are divergent in nature, the goal of every medical system has been to provide rational treatment to the diseases. The basic effort of every medical system is to bring homeostasis (balance) with one’s surroundings based on their medical philosophy to extend a healthy state to the sick and tackle diseases.

Factors of disease causation

Predisposing factors are the factors which create a state of susceptibility, making the host vulnerable to the agent. These are age, sex and previous illnesses.

Enabling factors are those which assist in the development of (or in recovery from) the disease; e.g. housing conditions, socio-economic status.

Precipitating factors are those which are associated with immediate exposure to the disease agent or onset of disease, e.g. drinking contaminated water, close contact with a case of pulmonary TB.

Reinforcing factors are those which aggravate an already existing disease, e.g. malnutrition, repeated exposures. 

Risk factors are the conditions, quality or attributes, the presence of which increases the chances of an individual to have, develop or be adversely affected by a disease process. The risk factor need not necessarily cause the disease but does increase the probability that the person exposed to the factor may get the disease easily.

Different concepts on causation of diseases

ANCIENT VIEWS

Demonic theory

Religion, philosophy and medicine were integral part in the early part of civilization. Religion recognized multiplicity of Gods, both good and evil. Philosophy accepted the influence of inanimate bodies such as sun, moon and stars on living bodies. Thus a co relation between these with health and disease was established in primitive ages.

One concept prevalent was that the evil spirit entering the body directly and pursuing nefarious actions.  Another concept was the evil spirit   as  a messenger of Gods giving warnings in the form of diseases. Some other concept was a human enemy with supernatural powers, send evil spirits to harm others. The souls of dead ancestors influencing his family members were another belief.

Demonic possession is held by many belief systems to be the control of an individual by a malevolent supernatural being. Expressions include erased memories or personalities, convulsions, “fits” and fainting as if one were dying, access to hidden knowledge and foreign languages, drastic changes in vocal intonation and facial structure, sudden appearance of injuries (scratches, bite marks) or lesions, and superhuman strength.

Many cuneiform tablets contain prayers to certain gods asking for protection from demons, while others asked the gods to expel the demons that invaded their bodies.

Punitive theory

Punitive theory has its origin with the religion with the belief that one's attitude toward the deity is responsible as a cause of sickness. From a period centuries prior to the Christian era down to the present time, there have been beliefs   that disease was a punishment meted out by an outraged God for the sins of the individual or the race. There are recorded statements in biblical writings where in punishment is meted  for  a sin of David,  with devastating plague in which the whole nation suffered and which was stayed only by David's repentance and the making of a sacrifice.

Such references are abundantly available in Hindu mythology also especially those related to eruptive fevers such as Small pox, Chicken Pox etc.

Humoral theory

The Greeks rejected the super natural theories and looked up on disease as a natural process. They advocated that the matter is made up of four elements- Earth, Air, Fire and Water and these elements have the corresponding qualities of being  Cold, Dry, Hot and Moist.  With this concept they hypothesized that these qualities are represented in the body by four humors- Phlem, yellow bile,  black bile and blood. According to this theory, the equilibrium among these humours characterizes health (eucrasia), and disequilibrium (dyscrasia) characterizes disease.

Hippocrates moved medicine from magic and metaphysics to give it a scientific basis. He introduced logic into medical thinking, elaborated the theory of humours and recognized the importance of the environment in health. He also suggested that an excess of one of the humours would result in various idiosyncrasies - hematic, phlegmatic, choleric and melancholic.

The theory of humours was known in India, China, Egypt and Greece.

Miasmatic theory

Miasmatic theory is based on the inference that the air arising from certain kinds of ground, especially low, swampy areas, was a cause of disease. Certain places were thus given a very evil reputation, because the ground was said to exude some invisible, insensible vapour, called it  miasm, which produced disease.

The invention of miasma was really beginning to be scientific medicine. People were searching for a material and natural causes, instead finding shelter on god or a devil. Rational thinking that something cannot come out of nothing was the basis of this concept. The fact that malaria was prevalent in the vicinity of swampy land, and some evidence that people who ventured out in these swampy places were more likely to get the disease, lent plausibility to this theory. It was the belief in the air as the causative agent that gave malaria its name, mal aria ('bad air' in Medieval Italian).

Hahnemann was fascinated with this concept and further studied the cause of chronic diseases.  He observed suppression of diseases with heroic treatment available at that time was a major basis for  many of the chronic diseases.  He brought out new concept that suppression of itch to a miasm called Psora and venereal diseases to Sycosis and Syphilitic miasms.

Contagion theory

Some Hippocratic writings recognized that consumption (tuberculosis) is contagious. However, contagion played little role in medical explanations of disease until the work of Fracastoro who published his major treatise on contagion. Girolamo Fracastoro (1478-1553), an Italian physician, contended that there is a large class of diseases caused by contagion rather than humoral imbalances.

This was based on the observation that persons could contract infections even if their humors are normally balanced. Fracastoro defined a contagion as a "corruption which develops in the substance of a combination, passes from one thing to another, and is originally caused by infection of the imperceptible particles”. He called the particles the seminaria (seeds or seedlets) of contagion. Fracastoro was unable to say much about the nature of these suspected particles; bacteria were not observed by van Leeuwenhoek until 1683, and their role in infection was not appreciated until the 1860s.

Fracastoro nevertheless discussed the causes and treatment of various contagious diseases. He described how contagion can occur by direct contact, by indirect contact via clothes and other substances, and by long-distance transmission. In addition, he stated that diseases can arise within an individual spontaneously. His book has chapters for the arrangement of contagious diseases. His theory remained influential for nearly three centuries, before being superseded by a fully developed germ theory.

MODERN VIEWS

Germ Theory

Germ theory was proposed by Louis Pasteur (1822 –1895) and Robert Koch (1843 –1910). Germ theory postulates that every human disease is caused by a microbe or germ, which is specific for that disease and one must be able to isolate the microbe from the diseased human being.

The Germ theory viewed diseases in terms of a causal network similar to that of Fracastoro, but with much more detail about the nature of germs and possible treatments.

Organisms that cause disease inside the human body are called pathogens. Bacteria and Viruses are the best know pathogens. Fungi, protozoa’s and parasites can also cause disease.  Infectious diseases are typically classified as bacterial, viral, protozoal and so on. Knowing what bacteria are responsible for a particular disease indicates what antibiotic treatment to apply. Diseases are said to be infectious or communicable if pathogens can be passed from one person to another.

Epidemiological Triad

The standard model of infectious disease causation under the epidemiological triad theory states that an external agent can cause diseases on a susceptible host when there is a conducive environment

Within the epidemiological triad the agent is known as a ‘necessary’ factor. It has to be present for morbidity, although it may not inevitably lead to disease. For the disease to occur it needs the combination of what have been called ‘sufficient’ factors. These would include a host, which might be an individual or group of individuals who are susceptible to the agent. Susceptibility might be on the basis of age, sex, ethnic group or occupation. Environmental factors can also be sufficient factors that combine with the agent    

The epidemiological triad can be applied to non-infectious diseases where the agent could be ‘unhealthy behaviours, unsafe practices, or unintended exposures to hazardous substances’

Epidemiological Tetrad

Agent

Host

Environment

Time

Multi factorial theory

When the knowledge on diseases increased, one theory was not able to explain the causation of all the diseases. This lead to multi factorial theory to find rational explanation.  Though many diseases are infectious, other causative factors such as Genetic, Nutritional, Immunological, Metabolic, Cytological factors were identified as the cause for specific diseases.

Sydenham (1644-1689), often- called the English Hippocrates, first gave the important thought that there are different specific things which should be held responsible for different diseases. Sydenham held that disease was the result of the effort made- by the body to throw off, to expel these iiateries inorbi, the dead materials within it,' which had made the trouble.' The important result of Sydenham's studies was that a little close intelligent observation upon the part of the doctor is worth more than any amount of dosing administered in blind observance of a preconceived notion.

It was a step away from the four humours and from other artificial, theories. In short, Sydenham did much to teach the medical profession the value and importance of "studying the case."

Sir William Osler (1849-1919), a legendary medical teacher and physician of wrote: “The practice of medicine is an art based on science, working with science, in science and for science.”

BEINGS theory

BEINGS concept postulates that human diseases and its consequences are caused by a complex interplay of nine different factors. By coining the first letters of these factors the theory is called BEINGS theory. These are (1) Biological factors innate in a human being, (2) Behavioural factors concerned with individual lifestyles, (3) Environmental factors as physical, chemical and biological aspects of environment,(4) Immunological factors,(5) Nutritional factors, (6) Genetic factors, (7) Social factors, (8) Spiritual factors and (9) Services factors, related to the various aspects of health care services.

Web of causation theory

The “epidemiological triad theory” was very effectively used by Leavel and Clark in explaining the natural history of disease and levels of prevention. The terms primary, secondary and tertiary prevention were first documented in the late 1940s by Hugh Leavell and E. Guerney Clark from the Harvard and Columbia University Schools of Public Health, respectively.  Both were pioneers in Public Health. Leavell and Clark described the principles of prevention within the context of epidemiologic triangle model of Causation of diseases of Host, Agent and Environment.

As per their concept, the primary prevention seeks to prevent a disease or condition at a pre-pathologic state; to stop something from ever happening. Primary prevention strategies emphasize general health promotion, risk factor reduction, and other health protective measures. These strategies include health education and health promotion programs designed to foster healthier lifestyles and environmental health programs designed to improve environmental quality.

Secondary prevention focuses on individuals who experience health problems or illnesses and who are at risk of developing complication. Activities are directed at early diagnosis and prompt intervention, thereby reducing severity and enabling the client to return to normal. Its purpose is to cure disease, slow its progression, or reduce its impact on individuals or communities.

Tertiary prevention occurs when a defect or disability is permanent and irreversible. It involves minimizing the effects of long-term disease or disability by interventions direct at preventing complications and deteriorations. Tertiary prevention strategies are both therapeutic and rehabilitative measures once disease is firmly established.

Wheel theory

As medical knowledge advanced, an additional aspect of interest that came into play is the comparative role of “genetic” and the “environmental” (i.e. extrinsic factors outside the host) factors in causation of disease.

The “triad” as well as the “web” theory does not adequately cover up this differential.

To explain such relative contribution of genetic and environmental factors, the “wheel” theory has been postulated.

The theory visualizes human disease in the form of a wheel, which has a central hub representing the genetic components and the peripheral portion representing the environmental component.

Like any wheel, the outer part (environmental component) has spokes (3 in this model) and the environmental component is thus divided into 3 sub components, representing the social, biological and physical components of the environment.

To maintain health one has to take regular exercises and adequate rest, follow personal hygiene, eat nutritionally balanced diet, abstain from the abuse of drugs and alcohol, take care of one’s mental well-being and develop social skills to interact in a positive manner within society.

References

Park’s Textbook of Preventive and Social Medicine, 21st edition

Leon Gordis, Textbook of Epidemiology,  4th edition.

Textbook of public Health and Community medicine, AFMC,2009

Measures of prognosis, Bloomberg School of Public Health,2008

CDC , Principles of Epidemiology in Public Health Practice, 3rd Edition

The Genius of Homeopathy Lectures and Essays on Homeopathic Philosophy
By Dr Stuart M. CLOSE

http://www.open.edu/openlearn/science-maths-technology/science/health-sciences/epidemiology-introduction/content-section-3.1

Feezer L W, Theories concerning the causation of disease, Minnesota State Board of Health Minneapolis, Minnii. http://ajph.aphapublications.org/doi/pdf/10.2105/AJPH.11.10.908

  • PUBLISHED DATE : May 11, 2016
  • PUBLISHED BY : Zahid
  • CREATED / VALIDATED BY : Dr. Eswara Das
  • LAST UPDATED ON : May 11, 2016

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