Microbiology Chapter 2 PDF

CHAPTER 2 Basic Concepts of Infectious Disease Copyright © 2020 W. W. Norton & Company 1 Objectives ▪ Describe the relationships among a host, its microbiome, and pathogens. ▪ Apply the basic concepts of pathogenesis to specific infections. ▪ Discuss how infectious diseases imp...

CHAPTER 2 Basic Concepts of Infectious Disease Copyright © 2020 W. W. Norton & Company 1 Objectives ▪ Describe the relationships among a host, its microbiome, and pathogens. ▪ Apply the basic concepts of pathogenesis to specific infections. ▪ Discuss how infectious diseases impact communities and how communities shape emerging pathogens. 2 The Broker’s Secret – 1 Scenario ▪ Brandon, a 30-year-old stockbroker living in Chicago, visited his physician’s office. ▪ When the nurse asked Brandon why he was there, he blushed and said that he wanted to wait to talk with his physician about his health problem. 3 The Broker’s Secret – 2 Signs and Symptoms ▪ In the physical exam, Brandon’s physician observed a small lesion that appeared to be leaking a clear fluid at the end of his penis, which Brandon said did not really hurt. ▪ In response to direct questions from his physician, Brandon stated that he was sexually active with more than one partner. 4 The Broker’s Secret – 3 Testing ▪ The physician quickly sent a sample of the fluid to the clinical laboratory. ▪ The sample was found to contain fast- moving corkscrew-shaped bacteria. 5 The Broker’s Secret – 4 Diagnosis and Treatment ▪ The diagnosis was syphilis, caused by Treponema pallidum. ▪ The physician gave Brandon a shot of long-acting penicillin, and the lesion rapidly disappeared. ▪ Brandon’s sexual partners were contacted and made aware of his diagnosis. 6 2.1 Normal Microbiota versus Pathogens Section Objectives ▪ Describe differences between “normal” microbiota and pathogens. ▪ Discuss the relationship between infection and disease and between virulence and pathogenicity. ▪ Differentiate between infectious dose and lethal dose. ▪ Discuss the fundamental attributes of a successful pathogen. 7 What Is a Pathogen? – 1 ▪ Many areas of the human body are colonized with microbes. The collection of all microbes on the human body is called the human microbiota. (Commensalism or mutualism organisms?) ▪ Colonization refers to the ability of the microbe to stay attached to the body surface and replicate. Adhesins enable the microbiota to attach to host cells. 8  Athlete’s foot is caused by the What Is a Pathogen? – 2 fungus Trichophyton rubrum. ▪ A pathogen is any bacterium, virus, fungus, protozoan, or worm (helminth) that causes disease in humans. ▪ Pathogenicity is the ability of the organism to cause disease. ▪ Parasites are microbes that cause harm- inducing infections. Ectoparasites Endoparasites The disease filariasis (elephantiasis). 9 The Lingo of Pathogenesis – 1 ▪ An infection occurs when a pathogen or parasite enters and begins to grow on the host. Most infections do not cause symptoms and go unnoticed. ▪ Disease occurs when the patient develops symptoms. During an acute infection, symptoms develop and resolve rapidly. ― The common cold A chronic infection involves symptoms that develop gradually and resolve slowly. ― Tuberculosis 10 The Lingo of Pathogenesis – 2 ▪ Primary pathogens are likely to cause disease after infection in a healthy host. Rapidly reproduce/increase in number Moderate to high virulence ▪ Opportunistic pathogens are less Pneumocystis jirovecii cysts in bronchoalveolar likely to cause disease in a healthy host. material. Low virulence ▪ Some pathogens have a latent state. Pathogen cannot be found in culture. 11 Cold sore The Lingo of Pathogenesis – 3 ▪ Virulence describes the level of harm caused by a pathogen following infection. (degree of disease) ▪ Virulence can be measured by Lethal dose 50% (LD50) Infectious dose 50% (ID50) 12 The Lingo of Pathogenesis – 4 13 The Lingo of Pathogenesis – 5 ▪ Aspects of the pathogen that contribute to virulence: Invasion, the entry of a pathogen into a living cell, where it then lives Invasiveness, the ability of a bacterial pathogen to spread rapidly through tissues 14 The Lingo of Pathogenesis – 6 ▪ The host range refers to the animals a pathogen can infect and produce disease in. Some organisms can infect only one type of host to produce disease. ― Narrow o Salmonella enterica serovar Typhi infects humans only. ― Broad o Salmonella enterica serovar Typhimurium infects other animals in addition to humans. 15 2.2 Basic Concepts of Disease Section Objectives ▪ Distinguish between the signs and symptoms of a disease. ▪ Explain the role of immunopathogenesis in infectious disease. ▪ Describe the five basic stages of infectious disease. 16 How Do We Define Disease? ▪ Disease is a disruption of the normal structure or function of any body part, organ, or system that can be recognized by a characteristic set of symptoms and signs. ▪ Infectious disease A disease caused by a pathogen (bacterial, viral, or parasitic) that can be transferred from one host to another 17 Signs, Symptoms, and Sequelae – 1 ▪ Diseases are identified by characteristic signs and symptoms. Signs can be observed by examination (objective marker of disease). ― Fluid-filled rash ― Fever of 40°C Symptoms are experienced by the person (subjective indicator of disease). ― Pain ― Fatigue ▪ A syndrome is a collection of signs and symptoms that occur together and collectively characterize a condition. 18 19 Signs, Symptoms, and Sequelae – 2 ▪ Many of the signs and symptoms of disease are caused by the host’s response to the infection, called immunopathology. Cells damage nearby host tissue when killing the microbe. ▪ After a disease resolves, pathological consequences called sequelae may develop. For example, the immune response to strep throat can cause heart damage weeks after the infection has resolved. 20 ▪ Study terminology from Table 2.1 “Terms Used to Describe Infections and Infectious Diseases”, only definitions. 21 Stages of an Infectious Disease – 1 ▪ Characteristic stages of an acute infectious disease 22 Stages of an Infectious Disease – 2 ▪ Public health agencies track disease rates and severity. Morbidity is the rate of illness due to a disease = How many are sick from a disease. Mortality is the rate of death due to a disease = How many died from a disease. 23 2.3 Infection Cycles and Disease Transmission Section Objectives ▪ Describe complex versus simple infection cycles. ▪ Differentiate between endemic, epidemic, and pandemic disease. ▪ Explain animal reservoirs and incubators. 24 Modes of Transmission – 1 ▪ The route of transmission from one person or animal to another is called an infection cycle. Horizontal transmission occurs when the infectious agent is transferred from one person or animal to the next. Vertical transmission occurs when the infectious agent is transferred from parent to offspring. 25 Modes of Transmission – 2 ▪ Cycles of infection can be simple or complex Direct contact transmission ― Organisms may spread directly from person to person. o Touching, kissing, sex… 26 Modes of Transmission – 3 ▪ Indirect Transmission Pathogens may spread indirectly through an intermediary, which may be living or nonliving. ― Airborne transmission ― Vehicles any medium that can transport infectious agents such as food, water, or air ― Fomites (inanimate objects) ― Vectors (ticks, mosquitoes) 27  Modes of Transmission – 4 Reservoir: Nonhuman animal, plant, human, or environment that can harbor the organism; a reservoir may or may not exhibit disease. 28 Reservoirs of Infection ▪ A reservoir is an animal (including humans) or an environment that normally harbors the pathogen. It may or may not exhibit the disease. ▪ An asymptomatic carrier harbors the potential disease agent but does not have the disease. Neisseria meningitidis is an important cause of meningitis. ― It has no animal reservoir and is maintained in the human population by asymptomatic hosts. 29 ▪ Study terminology from Table 2.2 “Terms Used to Describe Disease Transmission and Frequency” 30 Endemic, Epidemic, or Pandemic? ▪ Endemic disease is one that is always present in a community at a low rate, often in an animal reservoir. ▪ Epidemic disease is one in which the number of cases increases in a community in a short time. ▪ Pandemic disease is an epidemic that spreads worldwide. Influenza HIV COVID-19 31 Zoonotic Diseases – 1 ▪ Zoonotic diseases are infections of animals that can be transmitted to humans. Pathogens may or may not cause the animal reservoir to have a disease. Transmission may be direct or indirect “spillovers” from animal to human. ― Lyme disease: Pathogen does not cause disease in the animal host but does cause disease when bacteria “spill over” to humans. ― Ebola: Virus does cause disease in the animal host and also in humans. 32 Zoonotic Diseases – 2 ▪ Animal and insect reservoirs can also function as “incubators” for new infectious diseases yet to emerge in humans. Two different strains of influenza virus can infect the same animal (usually pigs) at the same time. The two viruses can exchange discrete chunks of their genomes, and a new virus—more infectious and deadly than either of the original forms—can emerge. 33 2.4 Disease Portals and Biosafety Section Objectives ▪ Describe the various portals of entry and exit for microbial pathogens. ▪ Discuss concepts of biosafety and biocontainment. 34 How Do Infectious Agents Gain Access to the Body? ▪ From one host to the next: Portals (routes) of exit/entry Fecal-oral: Portal is the mucosa of the GI tract. Skin: Portal is the skin epithelium. Respiratory: Portal is the mucosa of the respiratory tract. Urogenital: Portal is the mucosa of the genital and urinary tracts. Parenteral: Portal is through breaks in the skin. Entry via the eye: Portal is conjunctiva. 35 Portals of Entry/Modes of Transmission 36 2.5 Host Factors in Disease Section Objectives ▪ Define the biological features of human hosts that influence the course of an infection. ▪ Explain how host behavior can impact susceptibility to disease. 37  How Does Health or Lifestyle Factor into Contracting an Infectious Disease? – 1 ▪ Age: greatest susceptibility among the very young (under 3) and very old (over 60) ▪ Host genetic makeup: host receptors to which bacteria and viruses bind ▪ Host hygiene and behavior: hand washing/hand sanitizers proper cooking of food sexual activity ▪ Nutrition and exercise: good nutrition and moderate exercise enhances the immune system. 38  How Does Health or Lifestyle Factor into Contracting an Infectious Disease? – 2 Pre-existing conditions: chronic infections, autoimmune disease, cancer, innate or acquired immunosuppression Occupation: Health care workers, laboratory personnel, agricultural workers, hunters, prostitutes are at higher risk of exposure. Immune status and immunopathogenesis: Immune cells can cause collateral damage to the healthy host tissues. 39 Clicker Question 1 Based on the information in the graph below, which organism is more virulent? a) Agent 1 b) Agent 2 c) Both organisms are equally virulent. d) This answer cannot be determined from the graph. 40 Clicker Question 2 Mahdu comes to the clinic experiencing a fever, rash, and high blood pressure. He is experiencing a) symptoms. b) signs. c) symptoms and signs. d) a syndrome. 41 Clicker Question 3 An epidemic is a) the continuous but low-level presence of a disease in a community. b) an increase in the number of cases of a disease in a community. c) caused only by airborne viruses. d) a disease that rapidly spreads worldwide. 42 Clicker Question 5 According to the following graph, a) rates of malaria and forest loss are not correlated. b) rates of malaria increase with forest loss. c) rates of malaria decrease with forest loss. d) the number of malarial vector mosquitoes increases as forest loss increases. 43