Exam 3: Pathogenesis and epidemiology

Question 1

Infectious disease

Answer 1

A transmittable, clinically relevant, illness

Question 2

Morbidity

Answer 2

The state of being diseased or unhealthy, often times within a population

Question 3

Mortality

Answer 3

Death, often times within a population

Question 4

Pathogen

Answer 4

A microorganism that can cause disease

Question 5

Symptoms

Answer 5

Subjective characteristics of disease felt only by the patient

Question 6

Pathogenesis

Answer 6

The process of disease development

Question 7

Signs

Answer 7

Objective manifestations of disease observed or measured by others

Question 8

Syndrome

Answer 8

A group of symptoms that consistently occur together or a condition characterized by a set of associated symptoms

Question 9

Epidemiology

Answer 9

The branch of medicine that deals with the incidence, distribution, and possible control of diseases

Question 10

Incidence

Answer 10

Number of new cases of a disease in a given area during a given period of time

Question 11

Prevalence

Answer 11

Number of total cases of a disease in a given area during a given period of time

Question 12

Endemic

Answer 12

An illness that is prevalent in or peculiar to a particular locality region, or people

Question 13

Sporadic Disease

Answer 13

An illness that occurs at irregular intervals; having no pattern or order in time.

Question 14

Outbreak

Answer 14

A sudden and unexpected increase disease incidence over the expected number of cases

Question 15

Pandemic

Answer 15

An outbreak of disease that spreads rapidly and widely

Question 16

Epidemic

Answer 16

An outbreak of disease that spreads rapidly and widely within a contiguous geographic area.

Question 17

List and describe the three types of microbial symbiotic relationships

Answer 17

mutualism: relationship where both involved benefit (Bacteria in human colon)

Commensalism: relationship where one organism benefits and the other is unaffected (staphylococcus on skin)

Parasitism: Relationship that benefits one and harms the other (tuberculosis bacteria in human lung)

Question 18

Discuss normal microbiota. Where are they found? What benefits can they provide?

Answer 18

● Organisms that colonize the body’s surfaces without usually causing disease
● Found in areas exposed to external environment: skin mucous membranes, GI tract, respiratory
tract
● Types:
○ Resident microbiota: part of the normal flora throughout life and are mostly commensal
○ Transient microbiota: temporary colonizers that cannot persist because of competition
with resident microbes, immune system, or changes in the body
● Benefits
○ Compete with pathogens in niches to prevent colonization
○ Aid in digestion and produce essential vitamins
○ Stimulate immune system and provide defense mechanisms to help body recognize
harmful invader

Question 19

Differentiate between pathogens, opportunistic pathogens and non-pathogens

Answer 19

● Pathogens: cause disease in healthy hosts, breach defenses, survive in hostile environments
○ Ex: mycobacterium tuberculosis
● Opportunistic pathogens: cause disease when the host’s immune defenses are compromised or
when they invade unusual sites in the body
○ E. coli causing UTI when displaced from intestines
● Non-pathogens: do not typically cause disease, even in a healthy host, coexist with host harmlessly
or even benefit host

Question 20

Describe how microorganisms enter and exit the human host. What are the portals of entry and exit? How is infection transmitted to new host?

Answer 20

● Portals of entry:
○ Skin: cuts, abrasions, direct penetration
○ Mucous membranes:
■ respiratory tract most common entry point
■ Pathogens enter GI tract through ingestion
■ Urogenital tract infection through sexual contact or compromised mucosal
barriers
○ Placenta: cross placenta and infect fetus
○ Parenteral route: usually unnatural; injecting pathogens directly into tissues through needle
sticks, insect bites, trauma, etc.

● Portals of exit:
○ respiratory/salivary portals: coughing, sneezing, talking
○ GI tract: feces, vomit
○ Urogenital tract: urine, semen, vaginal secretions
○ Blood: infected blood transmitted through insect vectors/shared needles

Question 21

Discuss reservoirs of infection. List and describe the three types

Answer 21

● Sites where pathogens are maintained as a source of infection, most cannot survive outside host
● Three types:
○ Animal reservoir: zoonoses (animals that harbor pathogens that can infect humans)
■ Acquired through direct contact with animal or its waste, eating animal, or via
vectors like insects
■ Rabies, lyme disease

○ Human carriers: infected individuals who are asymptomatic but infective to others
■ Some individuals eventually get ill while others never do
■ Healthy carriers protected by their immune system

○ Nonliving reservoir: pathogens persist in soil, water, food, etc.
■ Presence of microorganisms due to contamination by feces/urine
■ Cholera in water

Question 22

Describe zoonoses.

Answer 22

● Diseases naturally spread from animal host to humans
● Acquired through:
○ Direct contact with animal or its waste
○ Eating animals or contaminated animal products (undercooked meat)
○ Bloodsucking arthropods
■ Vector transmission
● Humans are dead-end host to zoonotic

Question 23

Explain the stages of disease

Answer 23

Incubation:
-Pathogen first enters the body and begins to multiply
-No signs or symptoms

Prodromal period
-General, non-specific signs and symptoms
-EX: not feeling right in the morning (fatigue or illness?)

Illness
-Infection-specific and most severe signs and symptoms appear

Decline
-Immune system responds
-Declining signs and symptoms

Convalescence
-Pathogen is almost fully out of the body
-No signs or symptoms

Question 24

Compare and contrast the terms incidence and prevalence

Answer 24

Incidence
-Number of new cases of a disease in a given area during a given period of time

Prevalence
-Number of total cases of a disease in a given area during a given period of time

*They both refer to ways we track and measure the occurrence of diseases

Question 25

Explain the role of international and government agencies in disease control and prevention

Answer 25

● World Health Organization (WHO)
○ Leads global efforts to monitor disease outbreaks
○ Provide aid to affected areas
○ Implement disease prevention programs
● Department of Health and Human Services (HHS)
● US Public Health Service (PHS)
○ Primary division of HHS
○ US PHS Commissioned Corps is one of 8 uniformed services in the US
○ Federal agencies
■ Centers for Disease Control and Prevention (CDC)
● Tracks disease outbreaks
● Investigates public health threats
● Issues guidelines for controlling disease spread in US
■ Food and Drug Administration (FDA)
● Certify any pharmaceutical or medical device
■ National Institutes of Health (NIH)
● Biomedical research arm of US government
● Department of Homeland Security (DHS)
○ Bioterrorism
○ Federal emergency management agency (FEMA)
● Strategic national stockpile program (SNS)
● Biomedical advanced research development authority (BARDA) and project bioshield
○ BARDA is separate communicator between agencies and is independent from PHS
● Local and state agencies
○ Implement health measures such as vaccination programs
○ Public health education
○ Response to disease outbreaks within their jurisdictions

Question 26

Compare and contrast endemic, epidemic and pandemic.

Answer 26

Endemic: an illness that is prevalent in or peculiar to a particular locality region or people

Epidemic: an outbreak of disease that spreads rapidly and widely within a contagious geographic area

pandemic: an outbreak of disease that spreads rapidly and widely

*they are similar in the way that they all refer to the ways in which disease affects a group of humans

Question 27

Define nosocomial infection and discuss contributing factors

Answer 27

● Infection acquired in a hospital or healthcare setting
● Contributing factors:
○ Exogenous infections: acquired from healthcare environment
○ Endogenous infections: arising from patient’s normal microbiota due to changes in
healthcare environment like broad spectrum antibiotics
○ Iatrogenic infections: result from medical procedures such as surgeries or catheter insertion
○ Additional: poor hygiene practices, antibiotic resistance, invasive procedures

Question 28

How is infection transmitted to new host?

Answer 28

● Airborne transmission: pathogen suspended in air and travels >1 meter
○ Droplet nuclei can remain airborne for extended periods
○ sneezing
● Contact transmission: person-to-person transmission through physical interaction
○ Touching, kissing, sexual contact, animal-to person transmission
● Vehicle transmission: spread of pathogens via contaminated inanimate objects
○ Fomite: object that provides vehicle transmission, common in healthcare settings
○ Food, water, medical equipment
● Vector-borne transmission
○ Mechanical vectors: passive transport of pathogens on vector’s body
■ Flies carrying pathogens on their feet
○ Biological vectors: pathogen undergoes part of its life cycle inside vector
■ Mosquitoes, malaria
○ External
■ Passive carriage of pathogen on body of vector
■ No growth of pathogen during transmission
○ Internal
■ Vector carries
■ Harborage transmission: pathogen does not change within vector
■ Biologic transmission: pathogen changes within vector

Question 29

List specific types of virulence factors. Discuss how they work and how they influence pathogenesis.

Answer 29

● Pathogenicity: ability of microorganism to cause disease
● Virulence: degree of pathogenicity, contribute to pathogenicity
● Types:
○ Adhesion: fimbriae or capsules for ex attach to host cells and tissues
○ Toxins
■ Exotoxins: soluble proteins secreted by bacteria that damage tissue
■ Endotoxins: released upon death and trigger strong inflammatory responses; LPS in
outer membrane of gram-negative bacteria
○ Enzymes: help pathogens invade tissues and evade immune system
○ Antiphagocytic factors: prevent destruction by host immune cells