Question

Which of the following is not a component of the epidemiology triad?
1. Agent
2. Host
3. Surveillance
4. Environment

Answer 1

Correct Answer - Option 3 : Surveillance

Concept:-

• For the occurrence of a disease in man three things are required, namely AGENT, HOST and ENVIRONMENT.
• These three factors are referred to as the epidemiological triad.
• The disease cannot occur in the absence of any one of these three factors.

Agent factors-

• One of the first requirements for the occurrence of the disease is a disease agent. The disease agent may be living or non-living.
• The disease agents have been classified into 5 broad groups:

1. Biological agents: These are the living agents, e.g., viruses, bacteria, fungi, protozoa, etc. These are found in the reservoir of infection (e.g., man, animal, insect, soil).
2. Nutrient agents: These are proteins, fats, carbohydrates, vitamins, minerals and water. An excess or deficiency of nutrients may lead to nutritional diseases.
3. Physical agents: These are heat, cold, pressure, radiation, electricity.
4. Chemical agents: These may be metals (e.g., lead), fumes, dust, gases, etc.
5. Mechanical agents: Chronic friction and other mechanical forces may cause trauma, injuries and fractures.

Host factors-

• The host-related factors are :

1. Age: Certain diseases are more frequent in certain age groups than in others, e.g., measles in childhood, cancer in middle age, atherosclerosis in old age.
2. Sex: There are sex differences in disease occurrence. Diabetes is more frequent in females; and heart disease in males. No satisfactory explanation has been given for this difference.
3. Heredity: Harmful genes in the constitution may give rise to disease, e.g., haemophilia, colour blindness, albinism. A number of congenital defects (e.g. cleft palate, hare-lip, spina bifida) are due to genetic factors. Essential hypertension, diabetes, mental diseases are all thought to be due to genetic predisposition.
4. Nutrition: Poor nutrition is frequently associated with nutritional deficiency diseases (e.g., kwashiorkor, anaemia). There are also diseases associated with overeating such as obesity and diabetes.
5. Occupation: The occupation of the host may predispose him to certain occupational diseases, e.g., poisoning, silicosis, accidents. lead
6. Customs and habits: Certain customs are prejudicial to health. Smoking is related to oral and lung cancer; open-air defecation, by causing soil pollution, favours the spread of intestinal parasites.
7. Human behaviour Lack of physical exercise, indulgence in alcohol and certain drugs are known to affect health adversely.

Environmental factors-

• A healthy environment is crucial for the health and well-being of individuals and communities. For descriptive purposes, the environment is divided into three components.

1. Physical environment: Much of the ill-health in India is due to poor environment unsafe water, contaminated soil, poor housing, lack of disposal facilities for human excreta and solid wastes.
2. Biological environment: The causes of disease may be found in the biological environment, e.g., animals, insects, rodents, etc.
3. Social environment: The customs, habits, culture, education, the standard of living are all implicated in disease occurrence directly or indirectly.