Chapter 5 – Principles of Infection and Disease Flashcards
What are microbes?
Microscopic particles that inhabit almost every ecological niche on Earth.
Do most microbes cause disease?
No, most microbes do no transmit disease. Many pass over or through the human body without causing harm.
What is mutualism?
Relationship where both the microorganism and the human host benefit.
What is commensalism?
Relationship where the microorganism benefits from the human host (nutrient-rich environment) without harming or helping the host.
What are pathogens?
Microorganisms that negatively affect the human host, causing infections and damaging tissues.
What are the main causes of infectious diseases?
Caused by bacteria, viruses, protists, fungi, and prions.
What is a prion?
A protein particle that can cause disease (e.g., Bovine Spongiform Encephalopathy in cattle, Variant Creutzfeldt-Jakob Disease in humans).
How are prions unique?
They are misfolded proteins that trigger other proteins to misfold too. They don’t have DNA or RNA.
Which infectious agents are living cells?
Bacteria, protists, and fungi are living cells with cellular features.
Why are viruses not considered fully living?
They cannot reproduce without a host cell.
What is ecology?
The study of interactions between living organisms and their environment.
What is an ecological niche?
The specific location an organism inhabits, defined by its physical and chemical conditions.
How does the human body function as an ecological system?
The human body consists of different ecological niches that are inhabited by specialized microorganisms.
What are resident microflora?
Microbes that normally inhabit niches on the human body (e.g., in the mucosa of the nares, epidermis, colon, pharynx, urinary tract).
What are transient microbes?
Microorganisms that temporarily inhabit the body but do not establish permanent residence.
What is the resident microflora of the skin?
Staph. epidermidis
What is the resident microflora of the mouth?
Strep. viridans
What is the resident microflora of the stomach?
Helicobacter pylori
What is the resident microflora of the intestine?
Escherichia coli
What is the resident microflora on the urogenital tract?
Staphylococcus epidermidis, Enterococcus faecalis
What factors influence the type and number of microbes in the human body?
pH, temperature, nutrients, toxins = personal hygiene, diet, age, overall health, drugs, hormones
How do microbes alter their ecological niche when there is bacterial colonization?
They change conditions in their habitat by metabolizing nutrients and producing waste, affecting pH, oxygen, CO2 levels, nitrogen waste, fermentation products.
What are sterile compartments in the human body?
Areas free of microbes (e.g. the CNS, heart, kidneys, peritoneal cavity).
What happens when microbes colonize sterile areas?
Serious medical consequences, often leading to severe infections.
What are true pathogens?
Microorganisms that cause disease in almost any individual they infect.
What are opportunistic pathogens?
Microorganisms that only cause disease in individuals with weakened immune systems.
What factors influence susceptibility to infection?
e.g., age, toxins, nutrition, chronic disease, HIV, previous infections.
What is a secondary infection?
Occurs when a weakened immune system makes an individual more susceptible to another infection.
How do true pathogens differ from opportunistic pathogens?
True pathogens have stronger biological traits that enhance their ability to cause disease, whereas opportunists require a weakened host.
What are exotoxins?
Highly toxic proteins released by bacteria (e.g., Clostridia releases potent toxins).
What are endotoxins?
Lipopolysaccharides found in the cell walls of certain bacteria that are released when these bacteria die, causing fever and pain.
What three factors contribute to the occurrence of infectious diseases?
Interactions between the:
1. Infectious agent
2. Human host
3. Environment
What is a natural reservoir?
Habitat where an infectious agent normally lives and multiplies before being transmitted to a human host.
What is a portal of entry?
Site through which an infectious agent enters a susceptible human host.
What is a portal of exit?
Site where an infectious agent leaves the human host to be transmitted to others.
What is the chain of infection?
Process of infection transmission, including the infectious agent, reservoir, portal of entry, portal of exit, and mode of transmission.
Why is the chain of infection useful in healthcare?
Helps identify points where infection spread can be interrupted, aiding in disease prevention and control.
What is a reservoir of infection?
Source from which a microbe is acquired (e.g., humans, animals, soil, objects).
What are the two types of infection sources?
- Exogenous: from outside the body (e.g., air, soil, water, humans, animals).
- Endogenous: from within the body (e.g., intestine, urogenital tract, skin).
What are some infectious diseases found in human reservoirs?
STDs, measles, polio, mumps, streptococcal infections, small pox.
What are nosocomial infections?
Infections acquired in healthcare settings, where immunocompromised and infected individuals increase transmission risk.
What is a vector?
Organism or object that carries an infectious particle to a human host.
What is a biological vector?
A living organism that carries an infecting particle during part of its life cycle, playing an active role in the transmission of the infection.
What is a mechanical vector?
An organism or object that carries an infecting microorganism passively on its surface, without being infected itself.
Can an animal be both a biological and a mechanical vector?
Yes, an animal can be a biological vector if it is infected and transmits the infection to a human, or a mechanical vector if it carries the infection on its skin, hair, or teeth.
What is the portal of entry?
Site through which pathogens gain access to host tissues.
What is direct contact transmission?
Occurs when infected tissue or secretions come into contact with exposed mucous membranes (e.g., sexual contact, childbirth).
What is penetration transmission?
When pathogens disrupt passive surface barriers (like skin or mucous membranes), allowing microorganisms to access underlying tissue. This can happen through abrasions, burns, wounds, or bites.
What is ingestion transmission?
Oral intake of solid or liquids, which pass into the digestive tract, where pathogens can then enter and infect the intestinal wall.
What is inhalation transmission?
Occurs when microorganisms are breathed into the respiratory tract, where they can access the lungs and respiratory tract portals, including the alveoili.
What is the portal of exit?
Where an infectious agent leaves the body.
What is the respiratory portal of exit?
Infectious particles expel in respiratory droplets through breathing, talking, singing, laughing, coughing, or sneezing.
What is the intestinal portal of exit?
Pathogens being expelled in feces. If water, food, or surfaces become contaminated, the infection can spread via the fecal-oral route (e.g., Cholera, typhoid, amoebic dysentery, Norwalk virus).
What is the sexually transmitted portal of exit?
STIs spread through direct sexual contact, including contact with oral, anal, or genital mucosa, and skin.
Can the site of infection differ from the portal of entry?
Yes (e.g., malaria enters through the skin via a mosquito bite, but the infection occurs in the liver and RBCs).
What is pathogenicity?
Ability of a microorganism to cause disease. “Can it make you sick or not?”
What is virulence?
Degree of how severe the disease is. “How bad is it?”
What are virulence factors?
Molecular traits that allow pathogens to cause injury.
Enzyme VFs
e.g., mucinase, keratinase, hyaluronidase, streptokinase.
Toxins VFs
e.g., bacterial endotoxins from cell wall, bacterial proteins and other exotoxins.
Adhesion VFs
e.g., fimbriae, spikes, adhesion proteins.
Motility VFs
e.g., flagella, cilia.
Bacterial Defence VFs
e.g., slime capsules, mycolic acid.
What is the infectious dose?
Amount of infectious material required for infection to occur. More virulent organisms require a smaller dose to establish infection (e.g., Enterohemorrhagic E. coli requires 10 cells to cause infection, while Vibrio cholerae may need 100,000,000 cells).
What is a communicable infection?
When microbes are transmitted from person to person, animals to people, or indirectly via inanimate objects.
What is a non-communicable infection?
When a person’s own microflora causes infection due to immunocompression.
What is a carrier state?
When a person harbors a microbe without showing symptoms, but is capable of transmitting the infection to others.
What are incubation carriers?
Infected but symptoms haven’t appeared yet.
What are convalescent carriers?
Symptoms subside after treatment, but microbes remain.
What are latent carriers?
Microbe is in a dormant state, but can be transmitted later (e.g., HIV).
What are asymptomatic/chronic carriers?
Don’t show signs of symptoms.
What is a mechanical vector?
A person who carries an infectious microbe on their skin or clothing without being infected themselves.
What are Emerging Infectious Diseases (EIDs)?
New or newly recognized infectious diseases that have increased in incidence or have the potential to affect human populations globally (e.g., SARS-COV-2, Human SARS Coronavirus, Nipah, Ebola, Zika).
What is a significant bacterial challenge related to EIDs?
Antibiotic-resistant bacterial strains, as they make infections harder to treat and control.
What is Sepsis?
Pathophysiological syndrome caused by infection, marked by dysregulated responses in coagulation, endocrine, cardiovascular, inflammatory, and immune systems.
What is Systemic Inflammatory Response Syndrome (SIRS)?
Beginning stage of Sepsis, characterized by widespread inflammation throughout the body.
What is Septic Shock?
Prolonged, servere Sepsis.
What happens in Septic Shock?
Vascular permeability increases suddenly, causing fluid to shift from the vascular system to surrounding tissues, leading to low blood pressure, impaired organ perfusion, organ failure and death.
Who is at high risk for Sepsis and Septic Shock? And what is the most common condition that predisposes individuals to it?
Immunocompromised individuals, elderly, young children, those with co-morbidities. Pneumonia is the most common condition that predisposes individuals to Sepsis.
