Chain of Infection Components PDF

# Chain of Infection Components - The chain of components has six sections. ## Mode of transmission - The way the infectious agent can be passed on. - Can be from **human-to-human** or **nonhuman sources** by: ### 1- Contact - **Direct contact transmission** (touching, Sexual Contact) - **Indir...

# Chain of Infection Components - The chain of components has six sections. ## Mode of transmission - The way the infectious agent can be passed on. - Can be from **human-to-human** or **nonhuman sources** by: ### 1- Contact - **Direct contact transmission** (touching, Sexual Contact) - **Indirect contact:** - **Fomite** (nonliving surfaces contaminated with an infectious agent) like doorknobs, telephones, towels, cups, and utensils. ### 2- Airborne Aerosol - Infectious agents (bacteria, viruses, etc) are carried in the air via aerosols (long-lasting particles) ### 3- Respiratory droplet - An infected person coughs or sneezes on or near you the respiratory droplets can either enter directly into the nose or mouth or land on unwashed hands and spread. ### 4- Enteric (fecal-oral) - Spread from the feces of an infected individual to the mouth another individual - poor hygiene - food and water. ### 5- Vector-borne: - **Vectors:** The term “vector” applies to any living organism that can carry a disease-causing microbe such as mosquitoes, fleas, lice, and ticks. ### 6- Blood transfusion - Introduction of a pathogen via blood transfusion ### 7- Vertical (maternal-fetal) - Pathogen that is passed from mother to child either *in utero* (via the placenta), or during childbirth. ## Portal of entry - The way the infectious agent can enter a new host (through broken skin, the respiratory tract, mucous membranes, and catheters and tubes) ## Susceptible host - Young children, elderly, patients with chronic disease, malnutrition, immunocompromised ## Portal of exit - The way the infectious agent leaves the reservoir (through open wounds, aerosols, and splatter of body fluids including coughing, sneezing, and saliva) ## Infectious agent - The pathogen (germ) that causes diseases ## Reservoir - Includes places in the environment where the pathogen lives (**this** includes people, animals and insects, medical equipment, and soil and water) ## Why do people get infectious diseases? - People get infectious diseases when microorganisms overpower our host defenses (i.e., when the balance between the organism and the host shifts in favor of the organism). ### From the organism's perspective - The number of organisms to which the host, or person, is exposed. - The virulence of these organisms. - Incubation Period. ### From the host's perspective, - Immunity, age, gender, General health: malnutrition. # Establishing the Cause of Infectious Disease ## Germ theory (Koch's Postulates): - Robert Koch proposed that in order to conclude that a microbe causes a particular disease, these postulates must be fulfilled: 1. The same pathogen must be present in every case of the disease. 2. The pathogen must be isolated from the diseased host and grown in pure culture. 3. The pathogen from the pure culture must cause the same disease when it is inoculated into a new healthy susceptible animal host 4. The pathogen must be isolated from the inoculated Sick animal and must be shown to be the same original pathogen. # Characteristics of Infectious Disease ## Distribution of the Pathogen - Infections are often described according to the distribution of the causative agent in the body: ### Localized infection - The microbe is limited to a small area. - An example is a boil. ### Systemic (generalized) - The infectious agent is spread, or disseminated, throughout the body. - An example is measles. ## Duration of Symptoms - The course of an infectious disease includes several stages: ### Acute infections - Characterized by symptoms that have a rapid onset but last only a short time. - An example is strep throat. ### Chronic infections - Develop slowly and last for months or years. - An example is tuberculosis. ### Latent infections - The microbe continues to exist in host tissues, often within host cells, for years without causing any symptoms. - If there is a decrease in immune response, the latent infection may become reactivated and symptomatic. ## Course of Infectious Disease - The course of an infectious disease includes several stages: ### 1- Incubation period - The time between acquisition of the organism & the beginning of symptoms. - It varies from: - only a few days (common cold), - to several weeks (Hepatitis A) - to many months (rabies) - and even years (leprosy). ### 2- Illness - A phase that follows the incubation period. - A person will experience the signs and symptoms of the disease. ### 3- Convalescence - The phase that follows the illness. The person is recovering from the illness. ## Syndrome - Specific group of symptoms & signs that may accompany a particular disease. ## Symptoms - Subjective changes in bod function. e.g. pain. - Evidence of a disease that is experienced by the patient. - Cannot be measured. ## Sign - Objective changes in body function that can be measured e.g. fever. - Evidence of a disease that is observed by others (doctors, nurses, ...) - Can be measured. # Principles of Infectious Disease ## Pathogenicity - Microorganisms are classified according to pathogenicity (the ability to cause a disease) into: ### 1- Non-pathogen - A microorganism that does not cause disease. - It may be part of the normal flora. ### 2- Pathogen - A microorganism capable of causing disease in healthy individuals. ### 3- Opportunistic pathogen - Microbe able to cause disease only when the body's innate or adaptive defenses are compromised (immunocompromised), or when introduced into an unusual location. ## Virulence - The degree or intensity of pathogenicity. ## Virulence Factors (Determinants) - Attributes of a microorganism or virus that promote pathogenicity. # Host-microbe interaction ## Some Important definitions - **Colonization:** Establishment and growth of a microorganism on a body surface. - **Infection:** Infection is the entry and development or multiplication of an infectious agent in the body of man or animals. - **Disease:** Change from a state of health. - **Health:** A state of complete physical, mental and social well being. - **Etiology of the disease:** Study of the cause of a disease. ## Medical Microbiology - Is a science of studying micro-organisms that are associated with human disease. - This field focuses on - **Pathogens** - **Diseases** - **Body defenses** # Diagrams The document includes diagrams that illustrate: - **The chain of infection:** A cyclical diagram showcasing each stage of the chain of infection. - **Koch's postulates:** Diagrams that illustrate the steps involved in Koch's postulates for establishing the cause of infectious disease. - **The distribution of pathogens:** Images of blood cells containing bacteria, viruses, or toxins to illustrate bacteremia, viremia, septicemia, and toxemia. - **Localized vs. systemic infection:** Images of a boil and a baby with measles to illustrate the localized and systemic nature of infections. - **The course of infectious disease:** Diagrams of various stages of the course of an infectious disease. - **Types of infectious agents:** Images depicting different types of infectious agents, including bacteria, viruses, and fungi. - **Tuberculosis transmission:** A diagram showing the transmission of tuberculosis through respiratory droplets. - **Cushing's syndrome:** An illustration of Cushing's syndrome, showing the adrenal gland and the effects of the syndrome on the body.