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Natural History of disease I Pre & Pathogenesis Phases I Dr.Singh
Natural History of Disease: Understanding the Progression of Illness The Natural History of Disease refers to the progression of a disease in an individual over time, from the initial exposure to the causative agent to the final outcome—either recovery, chronic illness, disability, or death—in the absence of intervention. Understanding this natural timeline is crucial in public health for planning preventive, diagnostic, and therapeutic strategies. The concept provides the foundational framework for disease prevention and is central to epidemiology, community medicine, and clinical decision-making. It helps health professionals recognize the window of opportunity where interventions can be most effective and efficient. The natural history of disease is broadly divided into two phases: Pre-pathogenesis phase Pathogenesis phase 1. Pre-pathogenesis Phase This phase precedes the onset of disease and occurs in a healthy individual. The interaction between agent, host, and environment begins during this phase, potentially setting the stage for disease development. For example, exposure to tobacco smoke (agent) in a genetically predisposed individual (host) living in an urban area (environment) may initiate a disease process like chronic bronchitis. Primordial and primary prevention strategies are most effective during this phase. These include health promotion, lifestyle modifications, and specific protections such as immunization and use of safety equipment. 2. Pathogenesis Phase This phase begins when the disease process has actually started. It is further subdivided into: Early Pathogenesis (Preclinical/Subclinical Stage) The disease is present but not yet clinically apparent. There are no signs or symptoms, though pathological changes may be underway. Detection is possible only through screening or laboratory tests. For instance, early cervical dysplasia detected via Pap smear is a classic example. Clinical Stage The disease manifests through recognizable signs and symptoms. At this point, patients seek medical care. The focus now shifts to secondary prevention through early diagnosis and treatment. Advanced Stage If untreated, the disease may progress to complications, chronicity, disability, or death. Here, tertiary prevention like disability limitation and rehabilitation becomes necessary to improve quality of life. Applications in Public Health Understanding the natural history of disease helps in: Designing appropriate screening programs. Identifying the best stages for interventions. Predicting disease burden and outcomes. Planning preventive and curative healthcare services. It also forms the basis for levels of prevention, which align with different stages of the disease process: primordial and primary prevention act in the pre-pathogenesis phase, while secondary and tertiary prevention target various pathogenesis stages.
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Natural History of disease I Pre & Pathogenesis Phases I Dr.Singh
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- 2. Definition of Disease •Disease: Physiological or psychological dysfunction of the body. • Illness: Subjective feeling of being unwell. • Sickness: Social dysfunction; inability to perform social roles.
- 3. Theories of DiseaseCausation • Old Theories: Supernatural Theory: Diseases caused by curses or evil eyes. Ayurveda: Imbalance of Tridoshas Chinese Medicine:
- 4. Germ Theory ofDisease • Key Discoveries in Microbiology: • Louis Pasteur (1860): Bacteria in air. • Robert Koch (1877): Linked anthrax to bacteria. • Rapid discovery of pathogens:
- 5. Koch’s Postulates (Criteriafor causative agents): 1.Organism always found in disease lesions. 2.Must be isolatable from lesions. 3.Inoculation into animals reproduces disease. 4.Organism re-isolable from animal lesions.
- 6. Shift in Focus: •Fromempirical causes (e.g., bad air) to microbes. •Now recognized: Diseases result from multiple contributory factors. Key Limitations: • Not everyone exposed to pathogens develops the disease (e.g., tubercle bacilli exposure). • Some individuals harbor pathogens but remain asymptomatic (healthy carriers, e.g., typhoid carriers).
- 7. Epidemiological Triad • Diseasearises when equilibrium between disrupts
- 8. Theory of MultifactorialCausation (Web of Causation) • Pioneered by: Pettenkofer of Munich (1819–1901). •Diseases arise from multiple contributing factors, not just pathogens.
- 9. Factors Influencing Disease Social,Economic, Cultural, Genetic, Psychological Poverty, illetracy, Lifestyle-related (e.g., lung cancer, diabetes).
- 10. Natural History ofDisease Definition: • Evolution of disease in an individual from early stages to recovery or death, without intervention. • It signifies the way in which a disease evolves over a time from the earliest stage to its treatment as recovery, disability, or death, in the absence of treatment or prevention. •Best established by Longitudinal study Cohort study.
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- 14. • Period beforedisease onset. • Disease agent has not yet entered man but factors which favor its interaction with the human host are already existing in the environment. • Equilibrium = Health Disturbance = Disease process begins Pre - Pathogenesis Phase
- 16. Pathogenesis Phase • Thephase begins when the causative agent enters the body and starts the disease process. Process: 1. The agent reaches its site of action, multiplies, and disturbs the structure and function of the affected organ. 2. This leads to changes in blood and tissue fluids, resulting in the development of signs and symptoms. 3.Final outcome of the disease may be recovery, disability, death
- 17. • Host canbecome a clinical case, subclinical case or carrier • Stages 1. Early Pathogenesis Phase This phase in chronic is referred to as presymptomatic phase 2. Late Pathogenesis Phase By the time sign and symptoms appears the disease is already welladvanced into the late pathogenesis phase.
- 19. Agent Factors inDisease
- 20. Physical Agents Heat, cold,radiation, noise, atmospheric pressure, humidity.
- 21. Chemical Agents Endogenous: Exogenous: Dust,gas, fumes, metals, allergens. Urea, uric acid, bilirubin, ketones, calcium oxalate
- 22. Biological Agents Features neededfor disease: Infectivity: Ability to invade and multiply Pathogenicity: Ability to cause illness Virulence: Ability to cause severity and fatality.
- 23. Mechanical Agents Friction, force, injury,sprains, accidents
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- 25. Host Factors inDisease
- 26. Age measles in childrenhypertension in middle age
- 27. Gender Males Females Lung cancer,coronary heart disease. obesity, diabetes, hyperthyroidism
- 28. Ethnicity: • Example: Sickle-cellanemia common among Negroes, thalassemia in Mediterranean regions. Occupation: • Occupations determine both income and health risks (e.g., pneumoconiosis in miners). Literacy Level: • Higher literacy = Lower disease incidence.
- 29. Marital Status: • Higherrisk of cervical cancer among married women. • Higher risk of STDs and HIV among unmarried individuals. Nutritional Status: • Poor nutrition increases vulnerability to infectious diseases. Lifestyle Factors: • Risk behaviors like smoking, alcohol use, drug abuse, and lack of exercise contribute to disease development.
- 30. Environmental Factors inDisease
- 31. Physical Environment •Air, water,soil, food, etc.
- 32. Biological Environment Plants, animals,insects, rodents, microbes.
- 33. Psychosocial Environment/ Stressful situations/ Cultural Practices Death, divorce, loss of employment, etc., can lead to anxiety, depression, and physical ailments (e.g., hypertension, headache, asthma). Customs, beliefs, taboos, feeding/eating habits
- 34. Risk Factors inDisease Definition: • A risk factor is an attribute associated with the development of disease, especially noncommunicable diseases like coronary artery disease, cancer, diabetes, etc. • It may or may not be modifiable, and indicates potential for unfavorable outcomes (e.g., disease, disability, death).
- 35. Characteristics: • Modifiable RiskFactors: Can be changed or eliminated (e.g., smoking, lack of exercise, obesity, high cholesterol). • Nonmodifiable Risk Factors: Cannot be changed (e.g., age, sex, genetics, race, family history). Environmental Risk Factors: • Air pollution, water contamination, substandard housing, etc. Synergistic Effect: • Risk factors often act together (e.g., smoking + high cholesterol → increased risk of coronary heart disease).
- 36. Risk Groups (SusceptiblePopulations) Definition: • Groups exposed to or associated with risk factors, leading to higher morbidity and mortality due to physical, biological, or sociocultural factors. Significance: • These groups require targeted identification and healthcare services (Risk-approach).
- 37. Examples of At-RiskGroups: 1. Physical Situation: • Poor living conditions, overcrowding, lack of sanitation. 2. Biological Situation: • Age: Newborns (LBW), elderly. • Sex: Women of reproductive age. • Physiological State: Pregnancy, malnutrition. • Genetics: Strong family history of diseases. 3. Sociocultural Situation: • Socioeconomic class, lifestyle, habits, beliefs, customs, and traditions.
- 39. Iceberg Phenomenon of Disease VisibleTip (Clinical Cases): • The portion of the disease that is visible to healthcare providers (e.g., diagnosed and treated cases). Submerged Portion (Hidden Cases): • Latent, inapparent, asymptomatic, undiagnosed, or carrier cases that contribute to the ongoing prevalence of the disease in the community.
- 40. Examples: • Diseases likehypertension, diabetes, anemia, mental illness, and malnutrition often have a larger hidden morbidity (submerged portion) than the known cases. Challenge: • Detecting and controlling these hidden, undiagnosed cases remains a significant challenge in community health.
Editor's Notes
- #3 Vata (air) Pitta (bile) Kapha (mucus) Chinese Medicine: Imbalance between Yang (male) and Yin (female) principles.
- #4 Gonococcus (1847) Typhoid bacillus, (1880) Tubercle bacillus (1882) Vibrio cholerae (1883) Diphtheria bacillus (1884)
- #7 Explanation: Some individuals remain unaffected despite harboring pathogens due to a balanced equilibrium.
- #8 Key Concept:
- #9 Examples: Coronary heart disease: Smoking, poor diet, lack of exercise. Types: Modifiable: Obesity (changeable). Nonmodifiable: Sex (fixed, e.g., gallstones in women).
- #10 Importance: Essential for applying prevention at various stages of disease.
- #19 A substance, living or nonliving, or a force that initiates the disease process.
- #21 Endogenous: Urea, uric acid, bilirubin, ketones, calcium oxalate Exogenous: Dust, gas, fumes, metals, allergens.
- #22 Features needed for disease: Infectivity: Ability to invade and multiply. Pathogenicity: Ability to cause illness. Virulence: Ability to cause severity and fatality.
- #23 Friction, force, injury, sprains, accidents.
- #24 Excess or deficiency of nutrients (proteins, fats, carbohydrates, vitamins, minerals, water) causes disease.
- #25 Factors within an individual that influence the outcome of disease interactions.
- #26 Certain diseases are age-specific (e.g., measles in children, hypertension in middle age).
- #27 Men: Lung cancer, coronary heart disease. Women: , Disease-specific to sex: Prostate (men), pregnancy-related toxaemias (women).
- #28 Income: Key factor in standard of living and disease prevalence. Low income → Increased risk of infectious diseases. High income → Increased risk of noncommunicable diseases.
- #31 Air, water, soil, food, etc.
- #32 Plants, animals, insects, rodents, microbes.
- #33 Death, divorce, loss of employment, etc., can lead to anxiety, depression, and physical ailments (e.g., hypertension, headache, asthma). Stress can also contribute to risky behaviors (e.g., alcohol or drug abuse, violence, suicide). Cultural Practices: Customs, beliefs, taboos, feeding/eating habits influence community health.
- #35 Types of Prevention: Primordial Prevention: Modifying or eliminating modifiable risk factors to reduce disease occurrence.
- #37 Approach: The Risk-approach is a management tool, e.g., Maternal and Child Health (MCH) services, to provide targeted care.
- #39 Visible Tip (Clinical Cases): The portion of the disease that is visible to healthcare providers (e.g., diagnosed and treated cases). Submerged Portion (Hidden Cases): Latent, inapparent, asymptomatic, undiagnosed, or carrier cases that contribute to the ongoing prevalence of the disease in the community.