T.Y.B.Sc. Paper IV Unit III- Epidemiology PDF

T.Y.B.Sc. Paper IV Unit III- Epidemiology UNIT III Syllabus 3.1 Scope of epidemiology: Perspective of epidemiology, descriptive and analytical epidemiology, Epidemiological triad, Stages of disease, Screening of disease 3.2 Epidemiology of communicable disease: Defini...

T.Y.B.Sc. Paper IV Unit III- Epidemiology UNIT III Syllabus 3.1 Scope of epidemiology: Perspective of epidemiology, descriptive and analytical epidemiology, Epidemiological triad, Stages of disease, Screening of disease 3.2 Epidemiology of communicable disease: Definition of common terms 3.3 Dynamics of Disease transmission: Reservoir, Route of transmission, Incubation 3.2 Epidemiology of Communicable disease: Definition of common terms Epidemiology (Greek word epi- on or upon, demos- people, logos- study) It is the study of distribution and determinants of health-related problems in specific population and application of this study to control or eradicate those health problems. Distribution – Frequency, pattern Determinants – Causes, risk factors Population- neighborhood, school, city, state, country, global Following are the terms frequently used in epidemiological studies: Infection: Infection is the entry and development or multiplication and secretions of toxins in the body of an infectious agent (pathogen) in the body of man or animals. An infection does not always cause illness. Infectious disease: It is the manifestation of infection of a victim by a pathogen and is identified by a set of ‘symptoms. ’ Parasite / Pathogen: It is a causative agent – virus, bacterium, fungus, protozoan, nematode etc., which forcibly removes nutrients from the victim and discharges toxins to create illness. Host: It is the victim that feeds and harbors the parasite. Primary/Definitive host: It is called primary host when it harbors the parasite for most of the time and often as an adult parasite. Secondary/ intermediate host: When it harbors only terminal stage in the life cycle of the parasite or the adult parasite only for a short while (temporarily). Infestation: It is the establishment of the parasite in or on the body of host. 1 T.Y.B.Sc. Paper IV Unit III- Epidemiology Contamination: It is the presence (or release) of infectious agent in the abiotic environment of the host like soil, water, food, air, etc. Contagious disease: It is a disease spread by direct contact (for example, skin or sexual contact that can cause scabies and sexually transmitted disease respectively). Communicable disease: It is a disease that can be transferred from a man, animal or non–living environment to a victim. It may be communicated by infection, infestation or contagion (contact). Endemic disease: It is a disease confined to an area/community, recurring and not disappearing (malaria, typhoid, plague, etc. are the examples). Epidemic disease: It is a disease capable of spreading from the place of origin (or occurrence) in successively larger sphere (area) and not getting c onfined to an area or a community. Cholera, T.B., Hepatitis –A, etc. are the examples. Pandemic disease: It is a disease spreading fast and wide, crossing the borders of countries so that there are cases in many countries at the same time. AIDS, Influenza, Plague, Cholera etc. are the examples. Sporadic disease: It is a disease that occurs in few scattered areas at random. Polio is an example. Zoonosis: They are the diseases transmitted from animals to man or vice versa. The simplest definition of a zoonosis is a disease that can be transmitted from other vertebrate animals to humans. A slightly more technical definition is a disease that normally infects other animals, but can also infect humans. Epizootic: It is an epidemic in animals (mostly pets or comm ercially valuable animals) Immunity: Ability to resist the disease even though the pathogen invades. It is due to sensitization of the person naturally or artificially so that there is synthesis and accumulation of antibodies capable of deactivating or kil ling the pathogen or the toxins released by it. Susceptibility: It is the predisposition of a person to an infection. It may be due to lack of resistivity or genetic constitution or physiological defect or nutrient deficiency, which may increase the possib ility of a person to contract a disease. Incidence of disease: Occurrence or detection or report of new cases of a disease within a certain period (for example one year) in a community is incidence of disease. Prevalence of disease: The total of new and old cases of disease, in a given community, in certain duration, constitutes prevalence of diseases. Trachoma 2 T.Y.B.Sc. Paper IV Unit III- Epidemiology Incubation period: It is the time lapse between invasion of a victim’s body by a pathogen and its subsequent multiplication till enough toxins accumulates or enough damage is sustained for manifestation of symptoms of a disease. Prodomal period: It is a short period (1 to 4 days) marked by vague signs of the entry of a pathogen. Exact diagnosis of the disease is often impossible at this stage. Infective period: It is a period for which the victim can potentially spread the disease in a community. Control: It is the deliberate effort to contain the incidences of a disease or spread of a disease though the disease may persist in a community or locality. Eradication: It is the exclusion of a disease totally from all the areas or countries so that not a single case appears anywhere. Carrier: A person who harbors the disease-causing agent without himself getting affected but able to transmit the disease is called carrier. Temporary carrier: A person excreting pathogen for a short period only is a temporary carrier. It may be cholera or polio like disease that may have temporary carriers. Chronic carrier: A person who keeps on eliminating / exuding a pathogen for an indefinite, prolonged period is a chromic carrier. Typhoid, amoebiasis, HIV, etc. can be transmitted over long durations by the chromic carriers. Fomites: Inanimate or non–living articles, other than food & water, contaminated with a pathogen (infections discharges) capable of transferring the pathogen to a healthy person are fomites. Handkerchief, napkins, towels, toys, pencils, stencils, toothbrush, shaving, drinking etc. are fomites. Vector: It is the intermediate or secondary host, usually an arthropod that transmits an infectious agent from an infected person to a healthy one without itself getting affected. Mosquitoes are vectors of malaria. 3