Lecture 2 Slides: Basic Concepts of Infectious Disease PDF

CHAPTER 2 Basic Concepts of Infectious Disease Copyright © 2021 W. W. Norton & Company, Inc. 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 comm...

CHAPTER 2 Basic Concepts of Infectious Disease Copyright © 2021 W. W. Norton & Company, Inc. 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. § 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 What Is a Pathogen? – 2 § Parasites are microbes that cause harm-inducing infections. Ectoparasites Endoparasites § 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. 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 likely to cause disease in a healthy host. Low virulence § Some pathogens have a latent state. Pathogen cannot be found in culture. 11 The Lingo of Pathogenesis – 3 § Virulence describes the level of harm caused by a pathogen following infection. § 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 – Salmonella enterica serovar Typhi infects humans only. Broad – 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 102°F 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 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. 19 Stages of an Infectious Disease – 1 § Characteristic stages of an acute infectious disease 20 Stages of an Infectious Disease – 2 § Public health agencies track disease rates and severity. Morbidity is the rate of illness due to a disease. Mortality is the rate of death due to a disease. § The Centers for Disease Control and Prevention (CDC) publishes the Morbidity and Mortality Weekly Report, which discusses current outbreaks, statistics, and other health topics affecting people in the United States. 21 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. 22 Case History: A Hike, a Tick, and a Telltale Rash – 1 § Emma Katherine, a 21-year-old college student attending school in MA, started to feel sick during one of her classes. By the time she returned to her residence hall, she had a fever, nausea, headache, and body aches. Thinking it was the flu, she tried staying in bed, until she noticed a rash showing up on her arms—small, flat, pink, non-itchy spots. 23 Case History: A Hike, a Tick, and a Telltale Rash – 2 § At the health center, the PA asked Emma what activities she’s been involved in over the past month. She told the PA about a trip taken three weeks earlier to North Carolina, where she hiked and camped in the woods for a couple of days. Emma reported that a friend did notice a tick on her back one morning, which hadn’t been there the night before. The friend removed the tick and threw it in the woods. 24 Case History: A Hike, a Tick, and a Telltale Rash – 3 § Emma’s signs, symptoms, and travel history led the PA to suspect that Emma might have Rocky Mountain Spotted Fever (RMSF), caused by the bacterium Rickettsia rickettsii. § No one with Emma on the trip, or back at the college, had RMSF. § So how did Emma get this disease? 25 Modes of Transmission – 1 26 Modes of Transmission – 2 § 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. 27 Modes of Transmission – 3 § Cycles of infection can be simple or complex. Direct contact transmission – Organisms may spread directly from person to person. o Touching, kissing, sex 28 Modes of Transmission – 4 § Indirect Transmission Pathogens may spread indirectly through an intermediary, which may be living or nonliving. – Airborne transmission – Fomites (inanimate objects) – Vehicles such as food, water, or air – Vectors (ticks, mosquitoes) 29 Reservoirs of Infection § A reservoir is an animal (including humans) or an environment that normally harbors the pathogen. § 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. 30 Case History: The Third Pandemic – 1 § In 1884, Yong Ding was 38 years old and living in Canton in Southern China. Life was hard, but Yong Ding, a cook, still managed to support his family. § Disease was rampant that year. Victims of the Shuyi (rat epidemic) were stacked like firewood in the streets, five bodies high in places, waiting to be taken for burial. 31 Case History: The Third Pandemic – 2 § Then, one morning, Yong Ding noted the first sign of Shuyi, a darkened swelling in his armpit. Within days, Yong Ding began coughing blood, as the agent (a mystery at the time) spread through his bloodstream to his lungs. Once he saw the “bubo” (as the swelling was called), Yong Ding knew death was not far behind. § More than 60,000 died in what was to become known as the Third Pandemic of bubonic plague, caused by the bacterium Yersinia pestis. Rats were thought to be the reservoir, with the pathogen transmitted to humans by a flea vector. § Several pandemics of plague have occurred over the centuries, including the Black Death that killed more than a third of Europe’s population in the fourteenth century. 32 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 33 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. 34 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. 35 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. 36 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. 37 “Picking” a Portal 38 Biosafety and Universal Precautions – 1 § Standard Precautions are regulations designed by the CDC to protect medical personnel. 1. Perform proper hand hygiene. 2. Use personal protective equipment (PPE). 3. Maintain respiratory and coughing hygiene. 4. Use safe injection practices. 5. Handle sharps safely. 6. Practice patient isolation precautions. 7. Sterilize instruments and devices. 8. Clean and disinfect environmental surfaces. 39 Biosafety and Universal Precautions – 2 § In the laboratory, four levels of agent containment are employed depending on the biosafety level (BSL) of the infectious agent. BSL 1: low risk; basic precautions BSL 2: human pathogens causing mild disease; barrier precautions BSL 3: human pathogens causing serious illness; separate rooms, work done in a biosafety cabinet (BSC) BSL 4: high-virulence pathogens where exposure can be lethal; separate facilities 40 Biosafety and Universal Precautions – 3 41 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. 42 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. 43 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. 44 2.6 Global Change and Emerging Infectious Diseases Section Objectives § Explain how civilization has impacted emerging infectious diseases. § Explain how climate change can alter infectious disease patterns. 45 Are All Infectious Diseases Known to Us? – 1 § New infectious diseases are continually emerging or reemerging. An emerging disease is one that recently appeared in the population. A reemerging disease is a known disease whose incidence or range is increasing. § Global increases in death and disease are often connected with human activities that bring humans closer to disease reservoirs and vectors. 46 Are All Infectious Diseases Known to Us? – 2 47 This concludes the Lecture PowerPoint presentation for Chapter 2. For more resources, please visit https://stg-iig.wwnorton.com/michum2/full