Introduction Learning Objectives Flashcards
Discuss the importance of studying microbial/bacterial pathogenesis.
- Infectious diseases are a leading cause of death worldwide
- Healthcare associated infections (HAIs) are severe (can lead to sepsis or death) and also have a heavy financial burden on hospitals and society
What is the normal microbiota?
Microorganisms frequently found on or in the body of healthy persons
Define the three “internal” surfaces that are contiguous with the outside environment.
- Respiratory tract
- Upper: nose, nasal cavities, mouth, larynx, pharynx
- Lower: trachea, bronchial tree, lungs - Digestive tract: mouth to large intestine
- Genitourinary tract: anterior parts of urethra, vagina
Describe the anatomical locations for normal bacteria microbiota and list the frequent types at these locations.
- Skin: Staphylococcus, Corynebacterium, Propionibacterium acnes, Enteric bacilli
- Oropharynx: α-Hemolytic steptococci, Micrococcus, Corynebacterium, Neisseria, Haemophilus, Spirochetes
- Large intestine: Streptococccus (enterococci), Lactobacillus, Clostridium, Bacteriodes, enteric bacilli
- Vagina: Streptococcus, Lactobacillus, Bacteroides, Mycoplasma
What are the functions of the normal microbiota?
- Immune stimulation
- Keeping out invaders
- Human nutrition and metabolism
- Conversion of ingested compounds
Explain the three types of microbe-host interactions and give an example for each.
- Mutualism: relationship benefits both microbe and host (ex. most of the normal microbiota)
- Commensalism: relationship only benefits the microbe but the host isn’t harmed (ex. non-pathogenic E. coli in the intestinal tract)
- Parasitism: relationship benefits the microbe and harms the host, producing infection or disease (ex. viruses)
Define pathogen.
A microorganism capable of causing a disease
Define pathogenicity.
The ability of a microbial pathogen to infect its host and produce a disease
Define virulence.
The degree of pathogenicity
Define virulence factor.
Strategies that contribute to virulence
- Not associated with viability
Define opportunistic pathogen.
A microorganism that usual only causes infection in a damaged or
immunocompromised host
Describe the sources of opportunistic pathogens.
- Commensals when the host defense is compromised
- Commensals in different locations in the body
- Commensals that acquire pathogenicity
- Environmental microbes that are pathogenic to the immunocompromised
Compare and contrast infection and disease and define infectious disease.
- An infection is the establishment of a microbial pathogen while a disease is the clinical manifestation of damage to host cells and tissues (caused by the infection)
- Infectious disease: illnesses caused by infections
Define intoxication.
Disease caused by the ingestion of a preformed toxin without infection
Describe the 6 events in the establishment of a bacterial disease.
- Encounter: pathogen meets host
- Sources and transmission
- Exogenous infection
- Endogenous infection - Entry: pathogen enters host
- Preferred site of entry: tissue tropism
- Ingress vs. penetration - Spread: pathogen spreads from site of entry
- Dissemination - Multiplication: pathogen multiplies in host
- Threshold number to cause disease - Damage: by pathogen, host response, or both
- Outcome: pathogen or host wins or they coexist
Explain why the development of a bacterial disease may not involve all these six events.
Sometimes the outcome can occur earlier (not necessarily the sixth step), which then stops the development of the disease
List the three major reservoirs of infectious agents.
- Human reservoirs
- Animal reservoirs
- Nonliving reservoirs
Describe the two modes of transmission and assign a mode of transmission to each of the examples in Table 58.2.
- Direct transmission: infectious agent is transferred by direct contact (person to person, contact with soil/vegetation harboring infectious organisms)
- Indirect transmission: transfer of an infectious agent from a reservoir to a host by suspended air particles, inanimate objects (vehicles), or animate intermediaries (vectors)
Define zoonosis.
A disease of nonhuman animals. Many, but not all, zoonoses may cause disease in humans.
Define carrier of an infectious agent.
Organism carrying a pathogen but having no disease symptoms
Define fomite.
Nonliving reservoirs of infections agents
Define direct transmission.
Direct contact
- Person to person
- Contact with soil/vegetation
Define indirect transmission.
- Airborne (> 1 meter)
- Vehicle (fomites, water, food, blood)
- Vector (animals as mediator like mosquitos, flies, fleas, ticks, etc.)
Define airborne transmission.
Pathogen is transmitted through respiratory droplets in the air
Define waterborne transmission.
Pathogen is transmitted through consumption of contaminated water
Define foodborne transmission.
Pathogen is transmitted through consumption of contaminated food
Define bloodborne transmission.
Pathogen is transmitted when contaminated bodily fluids enter the bloodstream
Define vector-borne transmission.
Pathogen is transmitted when the vector bites someone
Define symptom, sign, and syndrome.
- Symptom: subjective; complaints from a person about a condition (“I feel feverish”)
- Sign: a measurement (ex. temperature, blood cell counts)
- Syndrome: a group of symptoms and/or signs that accompany a disease
Explain how an infectious disease may be classified.
- Communicable vs. noncommunicable
- Sporadic, endemic, epidemic, pandemic
- Acute, chronic, and latent
- Local and systemic infection
- Primary and secondary infection
- Emerging infectious diseases
- Healthcare associated infections
Define communicable, contagious, and noncommunicable diseases and give an example for each.
- Communicable/contagious disease: can be transmitted from one organism to another (ex. COVID-19)
- Noncommunicable disease: cannot be transmitted from person to person (ex. cancer)
Define sporadic, endemic, epidemic, pandemic and give an example for each.
- Sporadic: disease that occurs infrequently and irregularly (ex. rabies)
- Endemic: constant presence and/or usual prevalence of a disease or infectious agent in a population within a geographic area (ex. valley fever in central CA)
- Epidemic: increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area (ex. smallpox)
- Pandemic: epidemic that has spread over several countries or continents, usually affecting a large number of people (ex. COVID-19 pandemic)
Define acute, chronic, and latent disease and give an example for each.
- Acute: disease is short in duration (ex. common cold)
- Chronic: disease lasts for months or years (ex. diabetes)
- Latent: disease is asymptomatic because the infectious agent is not in active replication in dormant periods (ex. herpes)
Define local and systemic infection and give an example for each.
- Local: affects only one body part or organ (ex. UTI)
- Systemic: infection has spread via the blood stream and/or lymphatic system, therefore affecting multiple organs/tissues or the whole body (ex. sepsis)
Define primary and secondary infection and give an example for each.
- Primary: initial exposure to a particular pathogen (ex. flu)
- Secondary: infection that occurs when another infection has made the person more susceptible to disease (ex. bacterial pneumonia that follows the flu)
Define emerging infectious disease and give an example.
New diseases (ex. COVID-19)
Define healthcare associated infection and give an example.
Infection that occurs while a person is receiving healthcare for another condition (ex. ventilator-associated pneumonia)
Explain the importance of healthcare associated infections.
- Associated with increased morbidity and mortality
- Prolonged hospital stays for patients who acquire infections
- Financial burden on hospitals
- Limited treatment options due to the emergence of antibiotic resistant organisms
Describe the characteristics of HAIs.
- Host
- Broken skin/mucus membranes
- Suppressed immune system
- Disturbed microbiota
- Pathogen
- Opportunistic
- Often drug resistant
- Transmission
- Direct or indirect contact
List the sources of HAIs.
Describe the major types of HAIs and explain why these infections occur more commonly.
- Central Line-associated Bloodstream Infection (CLABSI): infection that occurs when germs (usually bacteria or viruses) enter the bloodstream through the central line
- Catheter-associated Urinary Tract Infections (CAUTI):
- Surgical Site Infection (SSI)
- Ventilator-associated Pneumonia (VAP)
Define ventilator-associated pneumonia.
Lung infection that develops in a person who is on a ventilator
Define central line-associated bloodstream infection.
Bloodstream infection not related to an infection at another site that develops within 48 hours of central line placement
- Occurs when bacteria or other germs enter the patient’scentral lineand then enter into theirbloodstream
List the organisms frequently associated with HAIs.
Define epidemiology.
The study of a disease with regard to its etiology, transmission, morbidity, mortality, and mortality rate
Use Lyme disease to illustrate the concerns of epidemiology.
- Etiological agent: Borrelia burgdorferi
- Transmission:
- Reservoir: white-footed mice (vector-borne)
- Ixodes tick or deer tick
- Young and mature adult ticks
- Morbidity and mortality: increase in Lyme disease cases over time
- Factors that influence the occurence of the disease
- Size of the reservoir
- Population of the deer tick
- Risk factors for the disease (ex. outdoor activities)
Define etiology.
The cause of a disease
Define morbidity.
The incidence of a disease
- The number of new cases in a particular population during a particular time interval
Define mortality.
Death
Define notifiable infectious disease and give 3 examples.
A condition or disease that must be reported by law to the U.S. Public Health Service
1. Malaria
2. Measles
3. Smallpox
What is the significance of reporting notifiable diseases?
Allows health officials to quickly identify outbreaks and control the spread of disease
Identify the functions of the CDC.
“CDC works 24/7 to protect America from health, safety and security threats, both foreign and in the U.S. Whether diseases start at home or abroad, are chronic or acute, curable or preventable, human error or deliberate attack, CDC fights disease and supports communities and citizens to do the same.”
