Definition of Disease


Concept of Disease

What is  Disease

Many attempts have been made to define disease.

Disease is an unhealthy condition of the body (or part of it) or the mind. Disease is a condition in which body health is impaired, a departure from a state of health, an alteration of the human body interrupting the performance of vital functions. From a sociological point of view, disease is considered a socio phenomenon, occurring in all societies and defines and fought in terms of the particular cultural forces prevalent in the society. The simplest definition of disease is just the opposite of health. Disease also donates the ability to be at ease i.e. any deviation from normal function or state of complete physical or mental well-being, since health and disease are mutually exclusive.

The World Health Organization (WHO) has defined health although criterion but not disease. This is because disease has many shades (Spectrum of diseases) ranging from in-apparent (sub-clinical) cases to serve manifest illness. Disease refers to the harmful departure from the normal functioning of the human system.

Disease can also be viewed as the malfunctioning or disturbance in the normal body physiology. It may be attributed to one causative factor or a conglomerate of factors (a web-of-causation). Disease may manifest in varying degrees, such that individuals may be able to attend to activities of daily living. In other cases disability or incapacitation may e experienced, and the person becomes unable to do a range of thing, or even to be conscious of self environment. In both cases the normal physiology of the body is impaired and the person can no longer manifest his optimal potentials. The disease state produces a negative influence on physical, mental and socio-environment capacity of the individual usually withdraws from activities due to incapacitation.

Types of Disease

Disease may be categorized by the types of causation agent, route of entry of infective agent, or by method of acquiring such disease. In the following examples, disease is categorized by mode of acquisition namely:

Communicable diseases caused by specific biological agents which can be transferred from an infected host (reservoir) to susceptible host (recipient). The agents usually affect body tissues and cause damage to tissues and organs of the body or may produce generalized disorder. This means that they are organic in nature and can attack specific part of the body even when generalization may result eventually. Examples of these includes; malaria, typhoid, tuberculosis, syphilis and Acquired Deficiency Syndrome (AIDS).

Non-communicable Diseases – as the name implies, non-communicable disease are not   transferable from person to person through physical or social interaction. Nevertheless, traits for the problem may be transferred genetically from parents to child while the child was conceived in the womb. Common examples are: Genetic disorder – sickle cell disease, mutation and mongolism.

  Others are:

 Nutritional diseases – anemia and kwashiorkor.

 Degenerative Diseases or Cardio-vascular diseases like Hypertension.

 Metabolic and endocrine – diabetes mellitus.

 Serological disorder – immunological problems.

 Occupational disorder – sight and hearing defects as well as pneumoconiosis.

 Neoplasm – new growth such as breast and cervical cancer, prostate cancer and leucopoenia.

 Allergies – Asthma and some skin diseases – psoriasis.

 Reservoirs of the Infection

 The pathogens (agents of communicable disease) of human infections are relatively fragile and survive   only is selected media. Any medium which provides a favorable environment or harbor for agents of   communicable disease are known agents of infection. It serves as the source of the disease.

 Reservoirs of human infections include.

-            Man, the greatest reservoir of organisms that pathogenic to him. They include:

 a.    Frank case of the disease;

b.    Sub-clinical infection;

c.    Carriers-chronic or permanent, incubatory and convalescent carriers.

-            Lower animals – including animals used as food (Bovine TB i.e from cow, tape worm from pig or           fish, etc). animals also act as vectors of disease (as in the case of animal bites as in rabies in dog,             rat,      etc.).

-      Non living things, e.g soil, food, fomites.


Disease Transmission of Human Infection

Disease transmission donates the spread or transfer of disease from one person to the other.

 Factors Affecting the Transmission of Disease

  The extent to which infectious diseases spread in the community depends on the degree and        frequency   of contact between susceptible individuals and the disease agents. Before transmission occurs, the   following conditions must be present (chain of transmission).

a.      Reservoir of infections (serves as source)

b.       Virulence or the ability of the agent to survive and multiply in an environment and be capable to enter    another host to initiate problem.

c.       Portal of exit from reservoir

d.        Mode of conveyance from reservoir or host

e.        Portal of entry into a new host: and the presence of a susceptible host.

Mode of Transfer of Infection

Mode of Transfer of Infection

Once an agent leaves the host it has to be transferred, conveyed or transported to a new host if the disease is to occur. This transfer is made by some vehicles namely;

(a)        Direct transmission, or (b) Indirect transmission. Direct transmission occurs when the agent is spread from one person to another without an intermediate object. However there has to be an association between host and the new host, without necessarily any physical contact. For instance respiratory diseases like tuberculosis could be spread by direct contact through coughing, sneezing, and so on. Similarly indirect transmission occurs when an intermediate object is involved in the conveyance of pathogens from reservoirs to new host. The mode of transmission maybe by contact, inhalation, infection and infestation, penetration or transplacental. Two basic requirements being about this. First, the organism must be virile or virulent enough to survive long after leaving the host; secondly, there has to be a vehicle of conveyance to transfer it to the new host.

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