Chapter 14: Infection, Infectious Diseases, and Epidemiology Flashcards
What are Symbiotic Relationships and what are the three types?
Symbiosis- to live together
Types of symbiosis:
Mutualism (both members benefit)
Commensalism (one member benefits where the other is unaffected)
Parasitism- one member negatively affects the other Any parasite that causes disease is called a pathogen
What are some examples of Symbiosis?
Mutualism- bacteria in the human colon
Commensalism- staphylococcus on skin
Parasitism- M. tuberculosis in lung
What are the terms used to describe normal microbiota?
Also termed normal flora and indigenous microbiota
Organisms that colonize the body’s surfaces without normally causing disease
Two types:
Resident microbiota (always present, part of normal microbiota throughout life, mostly commensal)
Transient microbiota (temporary, cannot persist due to competition, elimination by body’s defense cells, chemical/physical changes in body)
How is normal microbiota acquired?
Development in womb free of microorganisms (axenic)
Microbiota begin to develop during birthing process
Much of one’s resident microbiota established during the first months of life
What is an opportunistic pathogen?
Normal microbiota that cause disease under certain circumstances
How does a bacteria become an opportunistic pathogen?
Introduction of normal microbiota into unusual site in body Immune suppression
Changes in normal microbiota
Changes in relative abundance may allow opportunists to thrive and cause disease
What is a reservoir of infection and what are the three types?
Sites where pathogens are maintained as a source of infection
3 Types: Animal Reservoir Human Carriers Nonliving Reservoir
What are animal reservoirs? What are zoonoses?
Zoonoses- diseases naturally spread from animal host to humans (anthrax, plague, rabies)
Acquire zoonoses through various routes Direct contact, eating animals, bloodsucking arthropods
Humans are usually dead-end host to zoonotic pathogens
What are human carriers and what are the characteristics of a human carrier?
Infected individuals who are asymptomatic but infect others
Some individuals eventually develop illness with others never get sick
Healthy carriers may have defensive systems that protect them
What are and types of nonliving reservoirs?
Soil, water, and food can be reservoirs of infection
Presence of microorganisms often due to contamination by feces or urine
Meat, milk, and vegetables also harbor pathogens
Define Contamination
The mere presence of microbes in or on the body
Define Infection
When organisms evades body’s external defenses, multiplies, and becomes established in the body
What are the portals of entry?
Sites through which pathogens enter the body
4 Major Routes:
Skin Mucous Membranes Placenta Parental Route
Skin
Outer layer of dead skin cells acts as a carrier to pathogens
Some pathogens can enter through openings or cuts
Others enter by burrowing into or digesting outer layers of skin
Mucous Membranes
Line the body cavities that are open to the environment
Provide a moist, warm environment that is hospitable to pathogens
Respiratory tract is the most common site of entry (entry through nose, mouth, or eyes)
Gastrointestinal tract may also be a route of entry (must be able to survive acidic pH of stomach)
Placenta
Developing embryo forms an organ called a placenta through which it obtains nutrients from the mother
Typically forms effective barrier to pathogens
Pathogens may be able to cross the placenta and infect the fetus, cause spontaneous abortion, birth defects, and premature birth
E.g. Listeria, Treponema pallidum, Toxoplasma gondii
Occurs in about 2% of pregnancies
Parental Route
Not a true portal of entry
Means by which portal of entry can be circumvented
Pathogens deposited directly into tissues beneath the skin or mucous membranes
What is the role of adhesion in infection?
Adhesion- process by which microorganisms attach themselves to cells
Required to successfully establish colonies within the host
Use adhesion factors- Specialized structures (Adhesion disks, hooks, suckers)
Ligands: Adhesins in bacteria or attachment proteins in viruses
Ligands: Adhesins and Attachment Proteins
Attachment proteins help in adhesion
Found on viruses and many bacteria
Viral or bacterial ligand bind to host cell receptors, interaction can determine host cell specificity
Changing/blocking a ligand or its receptor can prevent infection Inability to make attachment proteins or adhesins renders microorganisms avirulent
Some bacterial pathogens attach to each other to form a biofilm
The Nature of Infectious Disease
Infection and disease are not the same thing
Infection- invasion of the host by a pathogen
Disease results if the invading pathogen alters normal body function, also referred to as morbidity and is any change in a state of health
What is the difference between signs and symptoms?
Symptoms- subjective characteristics of the disease felt only by the patient
Signs- objective manifestations of disease observed by others
Syndrome- group of symptoms and signs that characterize an abnormal condition
Asymptomatic, or subclinical infections, lack symptoms but may still have signs of infection
What is Etiology?
Etiology is the study of the cause of disease
Pasteur- Germ Theory of Disease (disease caused by infections of pathogenic microorganisms)
Robert Koch- developed a set of postulates to a prove that a particular pathogen causes a particular disease
Koch’s Postulates
4 Postulates to follow:
- The causative agent must be found in every case of the disease
- The agent must be isoalted and grown outside of the host
- The agent must be reintroduced into a healthy host and a change in health of the host must occur
- The causative agent must be found to be causing the changes of healthy in the experimental host
What are the exceptions to Koch’s Postulates?
Some pathogens cannot be cultured in the lab
Diseases may be caused by a combination fo pathogens and other cofactors
Ethical considerations prevent applying Koch’s postulates (require introduction of possible pathogen into a human)
Difficult to establish a single cause of disease (meningities, hepatitis, etc.)
Pathogens may be ignored as potential causes of disease
