Natural History of Diseases PDF

Natural History of Diseases BSc Medical Sciences: Epidemiology Assistant Prof. Dr. Soza Th. Baban Introduction and Review In session 6, we discussed: Disease surveillance is essential for detecting, responding to, and preventing outbreaks. Effective disease surveillance systems require accu...

Natural History of Diseases BSc Medical Sciences: Epidemiology Assistant Prof. Dr. Soza Th. Baban Introduction and Review In session 6, we discussed: Disease surveillance is essential for detecting, responding to, and preventing outbreaks. Effective disease surveillance systems require accurate data, timely reporting, and international cooperation. Different types of surveillance systems serve different needs, from local to global. Challenges, importance and the role of disease surveillance in preventing and controlling outbreaks. Learning objectives Explain the natural history of disease and the stages of disease progression and provided with case scenarios. Differentiate between communicable and non- communicable diseases in the context of natural history. Discuss how social, economic, and cultural factors affect disease progression. Let’s go through each of these points in detail!  CONCEPT OF DISEASE "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". 1 Disease is just the opposite of health - i.e., any deviation from normal functioning or state of complete physical or mental well-being. The term "disease" literally means "without ease" (uneasiness) - disease, the opposite of ease - when something is wrong with bodily function. "  Natural History of Disease It signifies the way in which a disease evolves over time from the earliest stage of its prepathogenesis phase to its termination as recovery, disability or death, in the absence of treatment or prevention. ❑ For an infectious disease, the exposure is a causative agent. ❑ For cancer, the exposure may be a factor that initiates the process, such as asbestos fibers ( toxic, carcinogenic and fibrous silicate minerals ) or components in tobacco smoke (for lung cancer), or one that promotes the process, such as estrogen (for endometrial cancer).  Natural History of Disease It signifies the way in which a disease evolves over time from the earliest stage of its prepathogenesis phase to its termination as recovery, disability or death, in the absence of treatment or prevention.  Natural History of Disease The natural history of disease is the uninterrupted progression of disease from its initiation to either spontaneous resolution, containment by the body’s repair mechanisms, or to a clinically detectable problem.  Natural History of Disease It signifies the way in which a disease evolves over time from the earliest stage of its prepathogenesis phase to its termination (outcome) as recovery, disability or death, in the absence of treatment or prevention.  Natural History of Disease Susceptibility Stage: Before the onset of the disease. Subclinical Disease Stage: Pathological changes occur, but no symptoms are present (e.g., incubation period for infectious diseases, latency period for chronic diseases). Clinical Disease Stage: Symptoms becomes visible, and the disease is diagnosed. Recovery, Disability, or Death: The final outcomes of the disease. Natural History of Disease Infectious disease as a model The natural history of disease in a patient The progression of the disease process (A): Biologic onset of disease. Often, this point cannot be identified because it occurs subclinically, perhaps as a subcellular change, such as an alteration in DNA. (P): Pathologic evidence of disease could be obtained if it were sought by population screening or by a physician. (S): signs and symptoms of the disease develop in the patient. (M): the patient may seek medical care. (D): The patient may then receive a diagnosis; (T): Treatment may be given; (OUTCOME): The subsequent course of the disease might result in cure or remission, control of the disease (with or without disability), or even death.  Natural History of Disease 1. Prepathogenic phase This refers to the period preliminary to the onset of disease in human. The disease agent has not yet entered human body, but the factors which favour its interaction with the human host are already existing in the environment. This situation is frequently referred to as “human in the midst of disease" or “human exposed to the risk of disease". Potentially we are all in the prepathogenesis phase of many diseases, both communicable and non-communicable.  Natural History of Disease 1. Prepathogenic phase The causative factors of disease may be classified as AGENT, HOST and ENVIRONMENT. An interaction of these three factors is required to initiate the disease process in human; - determine the onset of disease which may range from a single case to epidemics; - the distribution of disease in the community.  Natural History of Disease 1. Prepathogenic phase Screening is the application of tests to diagnose disease (or precursors) in an earlier phase of the natural history of disease, often in well people, or in a less severe part of the disease spectrum than is achieved in routine medical practice. Natural History of Disease 1. Pathogenesis phase In infectious diseases; The pathogenesis phase begins with the entry of the disease "agent" in the susceptible human host. Disease agents include: Biological agents → microbes Nutrient agents→deficiency in vitamins Physical agents → radiation Chemical agents → jaundice (serum bilirubin), heavy metals, insecticides Mechanical agents → chronic frinction Social agents → smoking Natural History of Disease 1. Pathogenesis phase The disease agent multiplies and induces tissue and physiological changes, the disease progresses through a period of incubation and later through early and late pathogenesis. Natural History of Disease 2. Pathogenesis phase It is useful to remember at this stage that the host's reaction to infection with a disease agent is not predictable. The infection may be clinical (clear symptoms) or subclinical (no symptoms at all); typical (e.g., fever and rash are typical symptoms of measles) or atypical (unusual symptoms) or the host may become a carrier with or without having developed clinical disease as in the case of diphtheria and hepatitis B. Natural History of Disease 2. Pathogenesis phase In chronic diseases (e.g., coronary heart disease, hypertension, cancer), this phase is referred to as presymptomatic phase. During the presymptomatic stage, the pathological changes are essentially below the level of the "clinical horizon". The clinical stage begins when recognizable signs or symptoms appear. By the time signs and symptoms appear, the disease phase is already well advanced into the late pathogenesis phase.  (Session7 – Scenario descriptions) Scenario 1: Outbreak of Measles in a Low-Income Urban Community Scenario 2: Rising Diabetes Rates in a Rural Community Scenario 3: Tuberculosis in an Overcrowded Refugee Camp  Communicable vs. Non-Communicable Diseases Communicable Diseases: Spread from one person to another (e.g., Flu, COVID-19). Usually have a clear incubation period and rapid progression. Non-Communicable Diseases: Chronic diseases not passed from person to person (e.g., Diabetes, Cancer). Often long-term, with a slower progression, influenced by lifestyle and environment.  Impact of Social, Economic, and Cultural Factors Factors that influence disease progression include: Social: Access to healthcare, education, and social networks. Economic: Income, employment, and the ability to afford treatment. Cultural: Beliefs, practices, and attitudes towards health and treatment.  Applying the Natural History of Disease in Public Health Public health strategies use the knowledge of disease progression to: Design effective interventions targeting early stages. Implement vaccination, screening, or early treatment programs. Monitor and assess outcomes based on disease patterns.  (Session7 – The worksheet) Applying the Natural History of Disease to Public Health Planning 1. Chronic Disease: Type 2 Diabetes 2. Communicable Disease: an outbreak of measles  Recap and Q&A Key Points from Today’s Lecture: Identified the stages of disease progression and discussed with different case scenarios. The social, economic, and cultural factors on disease progression discussed with the activity of applying the natural history of disease to public health planning and designing the intervention plan for chosen disease. Preparation for Next Session In the next session we'll explore the Descriptive studies in epidemiology. i. Read Chapter 4 (Pages 70-78) from "Parks Textbook of Preventive & Social Medicine" by K. Park. ii. Review Chapter 7 (Pages 149-177) from "Gordis Epidemiology" by Celentano DD and Szklo M. iii. Research examples of descriptive epidemiological studies and their contributions to public health. iv. Prepare to discuss the types and uses of descriptive studies in the next session.