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Similar to CM 1.3 Agent Host and environmemtal factors ,epidemiological triad ,multi factorial causation od disease.pptx
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CM 1.3 Agent Host and environmemtal factors ,epidemiological triad ,multi factorial causation od disease.pptx
- 1. 6/17/2022
- 2. Agent, Host, and Environmental factors, Epidemiological triad and Multifactorial causation Dr Anjali Mall 6/17/2022
- 3. Specific Learning objectives 1. Introduction and a brief history of the concept of health (10 mts) 2. To enumerate various concepts of causation of disease. (10 mts) 3. To describe and interpret the epidemiological triangle and agent, host, and environmental factors. (15 mts) 4. To explain the multifactorial and web of causation of disease with examples. (10mts) 5. Conclusion and MCQs (15mts) 6/17/2022
- 4. 1. Introduction and Brief History • Health is one of the most precious commodity. • Responsible for socioeconomic development of the country. • Democritus in 5th century BC-without health ,nothing is of use ,not money or anything else. • Concept of health is multidimensional. 6/17/2022
- 5. 6/17/2022
- 9. 2. Various concepts of causation of disease • Old theories • Modern theories – germ theory – epidemiological triad (tetrad) – multifactorial causation – socioeconomic, cultural, genetic, psychological – web of causation – wheel of causation 6/17/2022
- 10. Discovery of microbiology - turningpoint ▶ GERM THEORY OF DISEASE ▶ Microbes as sole cause of disease CONCEPT OF CAUSATION 17 Older theories • Supernatural theory • Theory of Humors • Concept of contagion • Miasmatic theory • Theory of spontaneous generation Contagion theory Miasmatic theory 6/17/2022
- 11. Limitations of Germ Theory • Why only some people suffer from the disease even after exposure • Why do certain people carry pathogens but do not show manifestations of the disease • Why a disease would be epidemic sometimes • It does not take into account the multi- factorial causation even in the diseases in which micro-organism is the “necessary cause”. 6/17/2022
- 12. 3. Epidemiological triad or triangle Epidemiological triad : Arose out of limitations of the Germ Theory of Disease Focuses on outcome of interaction of agent, host and environment More applicable to infectious diseases 6/17/2022 TIME
- 13. Epidemiological triad – 2/3 • Agents -Substance living or non-living, or a force, tangible or intangible, the excessive presence or relative lack of which may initiate or perpetuate a disease process – Biological – Physical – Chemical – Mechanical – Insufficiency or excess of factors, hormones, nutrients, parts, structural defects, chromosomal factors, immunological factors – Social 6/17/2022
- 14. Epidemiological triad – 3/3 • Host – Demographic – Biological – genetic, biochemical, immunological, physio functions – Social and economic condition – Lifestyle – Level of exposure – State of health and overall fitness 6/17/2022 Human host – SOIL ,Disease agent – SEED
- 15. Epidemiological triad – 4/3 • Environmen t – Physical, – Biological, – Psychosoci al 6/17/2022
- 16. Interpretation of the triad 6/3 • : Disease Characteristics: • Toxicity, virulence, infectivity • Susceptibility to antibiotics • Ability to survive outside body Interventions: • Eradicate • Genetically modify Interventions: • remove breeding grounds • Improve sanitations Interventions: • Educate • Change activity patterns • Quarantine Host Characteristics: • Age • Prior exposure • Susceptibility • Co-infection • Immune response Interventions: • Treat, isolate • Immunize • Nutrition Environment Characteristics: Climate Physical Structures Population Density Social Structure Interventions: Housing Quality Sanitation, Water Preventive Measures Interventions: • Protect • Educate • After exposures Agent Pathogen
- 17. An epidemiological triad of Malaria 5/3 • : Malaria Characteristics: • Plasmodium Interventions: • Eradicate • Genetically modify Interventions: • remove breeding grounds • Improve sanitations Interventions: • Educate • Change activity patterns Host Characteristics: • Age • Susceptibility • Immune response Interventions: • Treat, mosquito protective measures • Diet and nutrition Environment Characteristics: Climate Physical Structures Population Density Social Structure Interventions: Breeding places Chemical control Preventive Measures Interventions: • Protect • Educate Agent Pathogen
- 18. 4. Multifactorial causation : Pettenkoffer of Munich(1890-1901) proposed it in the 19th century Aimed to overcome shortcomings of Germ Theory of disease in causation of “modern” epidemic diseases Equal importance to – – Social – Economic – Cultural – Genetic – Psychological factors An advanced model of the Triangle of Epidemiology Replaces “agent” with “causative factors” Purpose to know, quantify and prioritize for modification 6/17/2022
- 19. Poor nutrition Low immunity Concurrent disease Poverty Overcrowding malnutrition Mycobacterium tuberculi Multifactorial causation :Example-TB
- 20. 6/17/2022
- 21. Web of Causation 1/4 Suggested by McMahon and Pugh. Ideally suited for chronic diseases where the agent is not known. Emphasizes breaking the weak link in the chain or web of causation to prevent and/or control disease. “Web of causation” considers all the predisposing factors of any type and their complex interrelationship with each other. Removal or elimination of just one link or chain may be sufficient to control the disease, provided that link is sufficiently important in the pathogenetic process. 6/17/2022
- 22. Web of Causation 2/4 26
- 23. Conclusion There are various concepts for the causation of diseases- • Germ theory of disease- agent and host • Epidemiological triad- interaction and interdependence with Agent, host, and environment and time • Multifactorial causation- multiple factors eg-non communicable disease –prioritize and work • Web of causation-chronic disease- every factor has equal weightage 6/17/2022
- 24. Self assessment tool(MCQ) 1. All of the following are components of the epidemiological triad Except a) Environment b) Agent c) Host d) Manpower 6/17/2022
- 25. (MCQ) 2. Web of causation is most appropriate – a) Mostly applicable to common disease b) Better for all the related factors associated with causation of disease c) Epidemiological ratio d) Helps to interrupt the risk of transmission 6/17/2022
- 26. (MCQ) 3. Epidemiological Web of causation theme was by • Louis Pasteur • Robert Koch • Mc Mohan and Pugh • None 6/17/2022
- 27. (MCQ) 4. Ability to induce clinically apparent illness is a) Infectivity b) Pathogenicity c) Virulence d) Communicability 6/17/2022
- 28. (MCQ) 5. Triangle of epidemiology stands for - a) Interaction of agent, host, and environment. b) Interaction of agent, host environment, and time. c) Interaction and interdependence of agent, host, environment, and time. d) None of the above 6/17/2022
- 29. References 1. WHO. Tech. Report Series 137. WHO. 1952. 2. WHO. Constitution Of World Health Organization. 1946. 3. WHO. Role of Health sector in Food and Nutrition. Tech. Report Series 137. Geneva. 1980. 4. IGNOU. Concepts in Nursing. Available online at: http://www.ignou.ac.in/edusat/BNS/BNS101-Blk2-3- 4/Block1en/38-66color.pdf 5. WHO. Ageing and Health. A health promotion approach for developing countries. WHO, Regional Office for the Western Pacific United Nations Avenue.Manila, Philippines;2000.11- 15. 6. Ghai OP, Gupta P. Essential Preventive Medicine. Vikas Publishing House Pvt Ltd. India;1999:23,817-819. 7. Park K. Park’s textbook of preventive and social medicine. 20th edition, 2009. Banarsidas Bhanot publishers, Jabalpur, India 6/17/2022
Editor's Notes
- Causation of disease has given various concepts- ranging from older theories to modern theories Older theories started from 10,000 years ago back till early 19th century which were based on supernatural theory ,bad air ,living things generation form non livng things These theories were followed by germ theory of disease given in 1960 by louis Pasteur when he demonstrated presence of bacteria in he air and dispaaproved the spontaneous generation of disease 1873 advanced germ theory was establsed 1877 Robert Koch showed that anthra is caused by bacteris After that gonocovvus,typhoid cholers ,TB, and diplhtehieria bacterium werediscovered and finally medicine shed the dogma of magic and superstition and wore the robe of scientific knowledged 1973 it
- Germ theory was given in 19th and early part of 20th century and it gained momentum Though it was a revolutionary concept still it changed in coming years by knowing that several other factors are also responsible for a given disease So it had its own imitation
- The agent is the cause of the disease A host is a human or animal who harbors the disease Environment is surrounding conditions external to animal or human that causes or allows the disease transmission Time is the incubation period The life expectancy of the host Duration of the course of illness
- Biological- bacteria ,fungus, metazoan, protozoa ,virus etc Physical –exposure to air cold heat radiation sound, pressure Chemical Endogenous –urea, creatinine, ketones, bilirubin Exogenous –metals fumes, dust gases by inhalation ingestion or inoculation Mechanical –chronic friction or other mechanical forces leading to crushing tearing, sprain Social factors poverty, smoking,unhealthy lifestyle, drugs , alcohol
- Man's victory over his physical environment has been responsible for most of the improvement in health during the past century. In most developing countries, defective environment (e.g., lack of sanitation) continues to be the main health problem. Man has altered practically everything in his physical environment to his advantage. In doing so. he has created for himself a host of new health problems such as air pollution, water pollution, noise pollution, urbanization, radiation hazards, etc. The increasing use of electrical and electronic devices, including the rapid growth of telecommunication system (e.g., satellite systems), radiobroadcasting, television transmitters and radar installations have increased the possibility of human exposure to electromagnetic energy. Man is living today in a highly complicated environment which is getting more complicated as man is becoming more ingenious. If these trends continue, it is feared that the very "quality of life" we cherish may soon be in danger. Biological The living things are the viruses and other microbial agents, insects, rodents, animals and plants. These are constantly working for their survival, and in this process, some of them act as disease- producing agents, reservoirs of infection, intermediate hosts and vectors of disease. For example, poverty, urbanization, migration and exposure to stressful situations such as bereavement, desertion, loss of employment, birth of a ~andicapped child may produce feelings of anxiety, depression, anger, frustration, and so forth; and these feelings may be accompanied by physical symptoms such as headache , palpitation and sweating. But these emotional states also produce changes in the endocrine, autonomic and motor systems, which, if prolonged and in interaction with genetic and personality factors, may lead to structural changes in various bodily organs. The resulting psychosomatic disorders include conditions such as duodenal ulcer, bronchial asthma, hypertension, coronary heart disease, mental disorders and socially deviant behaviour (e.g. , suicide, crime, violence, drug abuse). Of primary concern is coronary heart disease which may be related to lifestyle and psychosocial stress. In many countries, road accidents are now the principal cause of death in young people. It is related to psychosocial states such as boredom, anxiety, frustration and other pre-occupations that can impair attention.
- The primary mission of epidemiology is to provide information that results in breaking one of the legs of the triangle, thereby disrupting the connection among environment, host, and agent, and stopping the outbreak.
- As a result of advances in public health, chemotherapy, antibiotics and vector control communicable diseases began to decline - only to be replaced by new types of diseases, the so-called "modern" diseases of civilization, e.g., lung cancer, coronary heart disease, chronic bronchitis, mental illness, etc. As already mentioned. tuberculosis is not merely due to tubercle bacilli; factors such as poverty, overcrowding and malnutrition contribute to its occurrence. The doctrine of the one-to-one relationship between cause and disease has been shown to be untenable, even for microbial diseases, e .g., tuberculosis, leprosy. It is now known that diseases such as coronary heart disease and cancer are due to multiple factors. For example, excess fat intake, smoking, lack of physical exercise and obesity are all involved in the pathogenesis of coronary heart disease. Most of these factors are linked to lifestyle and human behaviour. Epidemiology has contributed significantly to our present-day understanding of the multifactorial causation of disease. This new model includes all facets of the communicable disease model, and to make it more relevant and useful with regard to today's diseases, conditions, disorders, defects, injuries, and deaths; it also reflects the causes of current illnesses and conditions. The purpose of knowing the multiple factors of disease is to quantify and arrange them in priority sequence (prioritization) for modification or amelioration to prevent or control the disease. The multifactorial concept offers multiple approaches for the prevention/control of disease.
- The "web of causation" considers all the predisposing factors of any type and their complex interrelationship with each other. Fig. 7 illustrates the complexities of a causal web of myocardial infarction (which is by no means complete). The basic tenet of epidemiology is to study the clusters of causes and combinations of effects and how they relate to each other (88). It can be visualized that the causal web (Fig. 7) provides a model which shows a variety of possible interventions that could be taken which might reduce. the occurrence of myocardial infarction. The web of causation does not imply that the disease cannot be controlled unless all the multiple causes or chains of causation or at least a number of them are appropriately controlled or removed. This is not the case. Sometimes removal or elimination of just only one link or chain may be sufficient to control disease, provided that link is sufficiently important in the pathogenetic process. In a multifactorial event, therefore, individual factors are by no means all of the equal weight. The relative importance of these factors may be expressed in terms of "relative risk" (see page 86).