Chapter 14 Principles Of Diseases And Epidemiology PDF

Chapter 14 Principles of Disease and Epidemiology Copyright © 2021 Pearson Education Ltd. All Rights Reserved Pathology, Infection, and Disease Pathology: the study of disease Etiology: the cause of a disease Pathogenesis: the development of disease Infection: invasion or colonizatio...

Chapter 14 Principles of Disease and Epidemiology Copyright © 2021 Pearson Education Ltd. All Rights Reserved Pathology, Infection, and Disease Pathology: the study of disease Etiology: the cause of a disease Pathogenesis: the development of disease Infection: invasion or colonization of the body by pathogens. Disease: an abnormal state in which the body is not performing normal functions Copyright © 2021 Pearson Education Ltd. All Rights Reserved  Relationships between the Normal Microbiota and the Host Symbiosis is the relationship between normal microbiota and the host (or between 2 organisms) – Commensalism: one organism benefits, and the other is unaffected – Mutualism: both organisms benefit – Parasitism: one organism benefits at the expense of the other Some normal microbiota are opportunistic Copyright © 2021 Pearson Education Ltd. All Rights Reserved Figure 14.2 Symbiosis Copyright © 2021 Pearson Education Ltd. All Rights Reserved Relationships between the Normal Microbiota and the Host Microbial antagonism (competitive exclusion) is a competition between microbes Normal microbiota protect the host by: – Competing for nutrients – Producing substances harmful to invading microbes – Affecting pH and available oxygen Copyright © 2021 Pearson Education Ltd. All Rights Reserved Disadvantages: Some members of the human microbiota can cause disease in certain cases: 1. Weakening or collapse of the immune system 2. Translocation into a sterile body site that are not supposed to be at (such as blader, kidneys, blood stream, lungs, peritoneal cavity, CNS, muscle tissue) 3. Overgrowth of some members of normal flora during antibiotic administration (sensitive members of normal flora die while resistant members overgrow) Note: members of microbiota that can cause disease are known as opportunistic pathogens (secondary pathogens). Copyright © 2021 Pearson Education Ltd. All Rights Reserved Human Microbiome Human Microbiome Project analyzes relationships between microbial communities on the body and human health Normal microbiota permanently colonize the host and do not cause disease under normal conditions Transient microbiota may be present for days, weeks, or months. Copyright © 2021 Pearson Education Ltd. All Rights Reserved Figure 14.1 Representative Normal Microbiota for Different Regions of the Body Copyright © 2021 Pearson Education Ltd. All Rights Reserved Human Microbiome Distribution and composition of normal microbiota are determined by many factors: – Age: physiological changes associated with human age affect microbiota – Nutrients: food habits of individuals or communities – Physical and chemical factors – Host defenses: which can be affected by genetic mutations that affect the immune system, age, AIDS, cancer, chemotherapy, diabetes, immunosuppressive drugs… – Mechanical factors – Antibiotics Copyright © 2021 Pearson Education Ltd. All Rights Reserved Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Infectious Diseases Some diseases have a well-known etiology, and have an etiology that is not completely understood or unknown. There are several categories of disease, such as: - Inherited (genetic) disease - Degenerative diseases - Infectious diseases: diseases that are caused by microorganisms Figure 14.3 Koch’s Postulates: Understanding Disease. Infectious Diseases Symptoms: changes in body function that are felt by a patient as a result of disease Signs: changes in a body that can be measured or observed as a result of disease Syndrome: a specific group of signs and symptoms that accompany a disease Copyright © 2021 Pearson Education Ltd. All Rights Reserved Classifying Infectious Diseases Communicable disease: a disease that is spread from one host to another Contagious diseases: diseases that are easily and rapidly spread from one host to another Noncommunicable disease: a disease that is not spread from one host to another Copyright © 2021 Pearson Education Ltd. All Rights Reserved Occurrence of a Disease Sporadic disease: disease that occurs only occasionally Endemic disease: disease constantly present in a population Epidemic disease: disease acquired by many people in a given area in a short time Pandemic disease: worldwide epidemic Copyright © 2021 Pearson Education Ltd. All Rights Reserved Severity or Duration of a Disease Acute disease: symptoms develop rapidly but the disease lasts only a short time Chronic disease: symptoms develop slowly Subacute disease: intermediate between acute and chronic Latent disease: causative agent is inactive for a time Copyright © 2021 Pearson Education Ltd. All Rights Reserved Extent of Host Involvement Local infection: pathogens are limited to a small area of the body Systemic infection: an infection throughout the body Focal infection: systemic infection that began as a local infection Copyright © 2021 Pearson Education Ltd. All Rights Reserved Extent of Host Involvement Primary infection: acute infection that causes the initial illness Secondary infection: opportunistic infection after a primary infection Subclinical infection: no noticeable signs or symptoms (inapparent infection) Copyright © 2021 Pearson Education Ltd. All Rights Reserved Extent of Host Involvement Sepsis: toxic inflammatory condition arising from the spread of microbes, especially bacteria or their toxins, from a focus of infection Septicemia: also known as blood poisoning; growth of bacteria in the blood. Bacteremia: presence of bacteria in the blood Toxemia: presence of toxins in the blood Viremia: presence of viruses in the blood Predisposing Factors Make the body more susceptible to disease – Gender – Inherited traits – Lack of vaccination – Fatigue – Age – Lifestyle – Nutrition – Chemotherapy Copyright © 2021 Pearson Education Ltd. All Rights Reserved Development of Disease Incubation period: interval between initial infection and first appearance of signs and symptoms Prodromal period: short period after incubation; early, mild symptoms Period of illness: disease is most severe, all disease signs and symptoms apparent. Period of decline: signs and symptoms subside Period of convalescence: body returns to its prediseased state Copyright © 2021 Pearson Education Ltd. All Rights Reserved Figure 14.5 The Stages of a Disease Copyright © 2021 Pearson Education Ltd. All Rights Reserved Reservoirs of Infection Continual sources of infection – Human reservoirs Carriers may have inapparent infections or latent diseases – Animal reservoirs Zoonoses are diseases transmitted from animals to humans – Nonliving reservoirs Soil and water Copyright © 2021 Pearson Education Ltd. All Rights Reserved Transmission 1.Contact Transmission 2.Vehicles Transmission Direct contact Airborne transmission Waterborne Congenital Foodborne transmission Indirect contact 3.Vectors Transmission transmission Mechanical transmission Biological transmission Copyright © 2021 Pearson Education Ltd. All Rights Reserved  Contact Transmission Direct contact transmission: requires close association between the infected and a susceptible host (person-to- person transmission) touching, kissing, and sexual intercourse, animal bites Congenital transmission: transmission from mother to fetus or newborn at birth passes placenta Indirect contact transmission: spreads to a host by a nonliving object Copyright © 2021 Pearson Education Ltd. All Rights Reserved Vehicle Transmission Transmission by an inanimate reservoir (Vehicle transmission is the transmission of disease agents by a medium) Airborne = refers to the spread of agents of infection by droplet nuclei in dust that travel more than 1 meter from the reservoir to the host Waterborne = pathogens are usually spread by water contaminated with untreated or poorly treated sewage Foodborne = pathogens are generally transmitted in foods that are incompletely cooked, poorly refrigerated, or prepared under unsanitary conditions. Both waterborne and foodborne transmission also provide a transfer of microbes by fecal-oral transmission. Copyright © 2021 Pearson Education Ltd. All Rights Reserved Vectors Arthropods, especially fleas, ticks, lice, and mosquitoes Transmit disease by two general methods – Mechanical transmission: arthropod carries pathogen on its feet – Biological transmission: pathogen reproduces in the vector; transmitted via bites or feces Copyright © 2021 Pearson Education Ltd. All Rights Reserved Figure 14.8 Mechanical Transmission Copyright © 2021 Pearson Education Ltd. All Rights Reserved Healthcare-Associated Infections Acquired while receiving treatment in a health care facility – Also known as nosocomial infections Affect 1 in 25 hospital patients – 2 million per year infected; over 70,000 deaths Copyright © 2021 Pearson Education Ltd. All Rights Reserved Healthcare-Associated Infections Result from: – Microorganisms in the hospital environment – Weakened status of the host – Chain of transmission in a hospital Compromised host: an individual whose resistance to infection is impaired by disease, therapy, or burns Copyright © 2021 Pearson Education Ltd. All Rights Reserved Figure 14.9 Healthcare-Associated Infections Copyright © 2021 Pearson Education Ltd. All Rights Reserved Figure 14.10 Principal Sites of Healthcare-Associated Infections Copyright © 2021 Pearson Education Ltd. All Rights Reserved Control of Healthcare-Associated Infections Universal precautions – Standard precautions: basic, minimum practices – Transmission-based precautions: supplemental to standard precautions; designed for known or suspected infections Contact precautions Droplet precautions Airborne precautions Copyright © 2021 Pearson Education Ltd. All Rights Reserved Control of Healthcare-Associated Infections Reduce number of pathogens – Handwashing – Disinfecting tubs used to bathe patients – Cleaning instruments – Using disposable bandages and intubation Infection control committees Copyright © 2021 Pearson Education Ltd. All Rights Reserved Emerging Infectious Diseases Diseases that are new, increasing in incidence, or showing a potential to increase in the near future Most are zoonotic, of viral origin, and likely to be vector-borne Copyright © 2021 Pearson Education Ltd. All Rights Reserved Emerging Infectious Diseases Contributing factors – Genetic recombination: New strains, such as E. coli O157:H7 and avian influenza (H5N1) – Evolution of new strains – Widespread use of antibiotics and pesticides Antibiotic-resistant strains – Changes in weather patterns Copyright © 2021 Pearson Education Ltd. All Rights Reserved Emerging Infectious Diseases Contributing factors – Modern transportation (e.g. Zika virus) – Insect vectors (e.g. mosquito) transported to new areas can transmit infections brought by human travelers – Ecological disaster, war, and expanding human settlement – Animal control measures may affect the incidence of a disease. The increase in Lyme disease in recent years could be due to rising deer populations resulting from the killing of deer predators. Copyright © 2021 Pearson Education Ltd. All Rights Reserved Morbidity and Mortality – Morbidity: incidence of a specific notifiable disease – Mortality: deaths from notifiable diseases  Morbidity rate: number of people affected in relation to the total population in a given time period  Mortality rate: number of deaths from a disease in relation to the population in a given time Copyright © 2021 Pearson Education Ltd. All Rights Reserved