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Transcript
Chapter 3 Practical Disease Concepts in Epidemiology What Is Disease? Disease is an interruption, cessation, or disorder of body functions, systems, or organs Diseases arise from infectious agents, inherent weaknesses, lifestyle, or environmental stresses Environment – all that is external to the human host (physical, biological, social, cultural, etc.) Causes of Disease Identifying the causes of disease and the mechanisms by which it spreads remains a primary focus in epidemiology The science and study of the causes of disease and their mode of operation is referred to as etiology Disease Transmission The ability of a disease to be transmitted from one person to another or to spread through the population is called communicability Classify acute and chronic diseases according to infectivity and communicability When an infectious disease is contagious, or capable of being communicated or transmitted, it is called a communicable disease HIV/AIDS Cholera Influenza Cryptosporidiosis What are two general types of disease transmission? Vertical transmission – transmission from an individual to its offspring through sperm, placenta, milk, or vaginal Horizontal transmission – transmission of infectious agents from an infected individual to a susceptible contemporary Pathogens Organisms or substances such as prions, bacteria, viruses, fungi, or parasites that are capable of producing diseases The ability to get into a susceptible host and cause disease is termed invasiveness The disease-evoking power of a pathogen is called virulence Toxins – kill pathogens by poisoning them Antibiotics work against pathogens because of their toxicity What are two general classifications of disease? Acute – disorder with sudden onset, relatively severe, and short duration of symptoms Chronic – less severe but of long and continuous duration, lasting over long periods, if not a lifetime Questions Are all infectious diseases communicable? What is an example of a chronic communicable disease? What is an infectious disease that is chronic? Examples of diseases according to selected classifications What are the major stages in the disease process? Stages relevant to most health-related states or events 1. Stage of susceptibility 2. Stage of pre-symptomatic disease • • Incubation period Latency period Stage of clinical disease 4. Stage of recovery, disability, or death 3. Natural course of communicable disease Breaking the Cycle Viability – The capacity of the pathogen or disease-causing agent to survive outside the host and to exist or thrive in the environment Viability – Guinea worm is 1 year Solution – Break the cycle for 1 year What are the five major categories of disease? Congenital and hereditary diseases Allergies and inflammatory diseases Degenerative diseases Metabolic diseases Cancer Congenital and Hereditary Diseases Familial tendencies toward certain inborn abnormalities Injury to the embryo or fetus by environmental factors Examples – Down syndrome, hemophilia, heart disease at an early age Allergies and Inflammatory Diseases Body reacting to an invasion of or injury by a foreign object or substance Degenerative Diseases Deterioration of body systems, tissue, and functions Often associated with the aging process Metabolic Diseases Cause the dysfunction, poor function, or malfunction of certain organs or physiological processes within the body leading to disease states Example – Cells may no longer utilize glucose normally causing diabetes Cancer Characterized by abnormal growth of cells that form a variety of tumors, both benign and malignant Common modes of entry into the body of infectious disease agents Respiratory Oral Reproductive Intravenous Urinary Skin Gastrointestinal Conjunctival Transplacental Zoonosis and Disease in Humans Animals can be the host, vector, or source of certain infections and diseases A zoonosis (plural, zoonoses) is an infectious organism in vertebrate animals (e.g., rabies or anthrax) that can be transmitted to humans through direct contact, a fomite, or vector The word comes from the Greek words zoon (animal) and nosos (ill) Common Zoonotic Diseases • • • • • • • • • AIDS Amebiasis Anthrax Bovine papular stomatitis Brucellosis California encephalitis Cat-scratch fever Colorado tick fever Cowpox • • • • • • • • • • • Dengue fever Dermatophilosis Leprosy Lyme disease Pasteurellosis Plague Q-fever Rabies Rat-bite fever Rickettsialpox Rocky mountain spotted fever • Salmonellosis • Shigellosis • Streptococcus infections • Tetanus • Trichinosis • Tularemia • Yellow fever • Zoonotic scabies Notifiable Diseases in the United States Notifiable diseases are those of considerable public health importance because of their seriousness Such diseases Cause serious morbidity or death Have the potential to spread Can be controlled with appropriate intervention Immunity and Immunizations Against Infectious Diseases According to the Centers for Disease Control and Prevention, if fewer than 80% of the children in a given area have been inoculated for one of the contagious diseases, the danger of serious outbreaks or localized epidemics remains; every unvaccinated child is at risk. What Is Active Immunity? Active immunity – The body produces its own antibodies. This can occur through a vaccine or in response to having a specific disease pathogen invade the body. What Is Passive Immunity? Passive immunity – acquired through transplacental transfer of a mother’s immunity to diseases to the unborn child Diseases for Which Vaccines Are Used • • • • • • • • • • • • • • Anthrax Cervical Cancer (HPV) Cholera Chickenpox Diphtheria German measles (rubella) Haemophilus influenzae type b (Hib) Hepatitis A Hepatitis B Influenza Japanese encephalitis Lyme disease Measles Meningitis • • • • • • • • • • • • • • Mumps Pertussis Plague Pneumonia Polio Rabies Smallpox Spotted fever Tetanus Tuberculosis Typhoid fever Typhus Whooping cough Yellow fever What Is Herd Immunity? Viewed as the resistance a population has to the invasion and spread of an infectious disease Based on the notion that if a population or group is mostly protected from a disease by immunizations (say 80% or more), then the chance of a major epidemic occurring is highly limited Estimated herd immunity thresholds for vaccine-preventable diseases Is there a changing emphasis in epidemiology? Increasing life expectancy in modern times and higher levels of chronic disease has produced a change in the emphasis of epidemiologic studies Host-Related Control and Prevention Isolation applies to persons who are known to be ill with a contagious disease. It is often conducted on an inpatient basis in hospitals or nursing homes. Most state laws, as well as accrediting organizations, require one or two beds to be kept, designated, and equipped in a hospital or nursing home as isolation beds. Host-Related Control and Prevention Quarantine applies to persons who have been exposed to a contagious disease but may or may not become ill What Is Malnutrition? A condition that arises when the body does not get the right amount of vitamins, minerals, and other nutrients to maintain healthy tissues and proper organ function. Malnutrition occurs in people experiencing either undernutrition or overnutrition. What are some common nutritional deficiency diseases and disorders? Kwashiorkor – protein deficiency Marasmus – protein-calorie malnutrition, chronic undernutrition Iron-deficiency anemia Folic acid-deficiency anemia Vitamin B12-deficiency anemia Xerophthalmia – vitamin A deficiency Endemic goiter – iodine deficiency Beriberi – thiamine deficiency What are some common nutritional deficiency diseases and disorders? Ariboflavinosis – riboflavin deficiency Pellagra – niacin and amino acid tryptophan deficiency Scurvy – vitamin C deficiency Rickets – vitamin D deficiency Tetany – mineral deficiency Osteomalacia and osteoporosis – impaired calcium and phosphorus metabolism affecting bone formation Undernutrition A consequence of consuming too little essential vitamins, minerals, and other nutrients, or excreting them faster than they can be replenished Inadequate intake may result from excessive dieting, severe injury, or serious illness Excessive loss may result from diarrhea, heavy sweating, heavy bleeding, or kidney failure Overnutrition The consumption of too much food, eating too many of the wrong things, too little physical activity and exercise, or taking too many vitamins or dietary supplements Selected Chronic Diseases and Conditions Cardiovascular disease, cancer, chronic obstructive pulmonary disease, diabetes mellitus, and mental health disorders Chronic diseases are not typically caused by an infectious agent (pathogen), but result of genetic susceptibility, lifestyle, or environmental exposures Some exceptions are cancers of the cervix, liver, and stomach Characteristics of Chronic Diseases The latency period for chronic diseases is typically more difficult to identify than is the incubation period for acute infectious diseases This is explained by the multifactorial etiology that characterizes many chronic diseases Disability Umbrella term for impairments, activity limitations, and participation restrictions Impairments – any loss or abnormality of psychological, physiologic, or anatomic structure or function Activity limitations – difficulties an individual may have in executing activities Participation restrictions – problems an individual may experience in involvement in life situations