Pathogenesis and Epidemiology

Question 1

List and describe three types of microbial symbiotic relationships:

Answer 1

draw table

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 2

Discuss normal microbiota.

Answer 2

Microbiota:
- 10^14 prokaryotic cells and only 10^13 is eukaryotic
- Organisms that colonize the body’s surfaces without normally causing disease
- Can be commensal, mutualistic, or pathogenic
- They are found everywhere in the human body

two types - resdident and transient microbiota

Question 3

resident Microbiota

Answer 3

Are part of normal microbiota throughout life
Are mostly commensal

Question 4

Transient Microbiota

Answer 4

1. Found is some regions as resident microbiota
2. Remain in the body for short period of time
3. Cannot persist in the body through… so eventually end up dying - short period of time

• Competition from other microorganisms
• Elimination by the body’s defense cells
• Chemical or physical changes in the body

Question 5

Acquisition of normal microbiota:

Answer 5

• The womb is an axenic (free of microorganisms)
• Microbiota begin to develop during birthing process
• Much of one’s resident microbiota established during first months of life

Question 6

Benefits of normal Microbiota

Answer 6

• Assist in various bodily functions (digestion in large intestine)
  -Can protect from pathogens that enter the body
• Drug metabolism
• Maintains structural integrity of gut
• Immunomodulation

Question 7

opportunistic pathogens,

Answer 7

Opportunistic Pathogens:

Normal microbiota that cause disease under certain circumstances
- Introduction of normal microbiota into unusual site in body
- Immune suppression
- Immunocompromised
- Changes in the normal microbiota
- Changes in relative abundance may allow opportunity for a member to thrive and cause disease
- Broad spectrum antibiotics

Question 8

Non-pathogenic:

Answer 8

Non-pathogenic:
Organisms that do not cause disease

Question 9

Pathogenic:

Answer 9

Pathogenic:
Microorganisms that can cause disease in virtually an host

Question 10

what are the three types of reservoirs of infection.

Answer 10

Animal reservoir
human carrier
nonliving reservoir

Question 11

describe animal reservoir and include soonoses

Answer 11

Zoonoses (learning objective in itself so know this)
- Diseases naturally spread from animal host to humans
- EX: rabies, black plague, lyme disease, west nile virus
Acquire zoonoses through various routes
- Direct contact with animal or its waste
- Eating animals
- Bloodsucking arthropods
Humans are usually dead-end host to zoonotic pathogens

Question 12

describe human carriers

Answer 12

• Infected individuals who are asymptomatic but infective to others
• Some individuals eventually develop illness while others never get sick
• Healthy carriers may be protected by their immune system

Question 13

describe nonliving reservoir

Answer 13

Soil, water, and food can be reservoirs of infection
- Presence of microorganisms often due to contamination by feces or urine

Question 14

what is transmission

Answer 14

Disease transfer from a reservoir or a portal of exit to another host’s portal of entry

Question 15

what are the four groups of transmission

Answer 15

1. airborne
2. contact transmission ( direct contact or droplet)
3. vehicle transmission ( indirect contact w/ water-borne/body fluid)
4. Vector-borne transmission ( biological host/mechanical (physical proximity))

Question 16

explain airborne transmission

Answer 16

Pathogen suspended in air and travels >1 meter
Droplet nuclei
- Small particles (1-2 um diameter)
- Can remain airborne for long time
- Can travel long distances
- Usually propelled from respiratory tract of source organisms by sneezing, coughing, or vocalization

Question 17

explain Contact Transmission (direct contact or droplet)

Answer 17

Coming together or touching of source/reservoir and host
Direct contact (person-to-person)
- Physical interaction between source/reservoir and host (kissing, touching, sexual contact)
- Person to animal
Droplet spread
- Large particles (>5um) that travel <1 meter

Question 18

explain vehicle transmission (indirect contact/ water-borne/body fluid)

Answer 18

Vehicle
- inanimate materials or objects involved in pathogen transmission (single vehicle spreads pathogen to multiple hosts)

Indirect contact
- Involves an intermediate (usually inanimate)

Common vehicle transmission
- Water and food
- Fomite
—–Term for object that provides vehicle transmission
——Common in healthcare settings

Question 19

explain Vector-Borne transmission (biological host/mechanical (physical proximity)

Answer 19

external (mechanical) transmission
- Passive carriage of pathogen on body of vector
- No growth of pathogen during transmission
- Usually through the bite of insect

internal transmission
- Carried within vector
- Harborage transmission
——Pathogen that does not undergo changes within vector
- Biological transmission
—–Pathogen undergoes changes within vector

Question 20

what are portals of entry?

Answer 20

Sites through which pathogens enter the body

Question 21

what are the four main portals?

Answer 21

1. skin
   - outer layer of dead skin cells acting as a barrier to pathogens
   - Some pathogens can enter through openings or cuts
   - Others enter by burrowing into or digesting outer layers of skin
2. mucous Membrane
   -Line the body cavities that are open to the environment
   - Provie moist, warm environment hospitable to pathogens
   - Respiratory tract is the most common site of entry (Entry is through the nose, mouth, or eyes)
   - Gastrointestinal tract may be route of entry
   (Must survive the acidic pH of the stomach)
3. placenta
   - Typically forms effective barrier to pathogens
   - Pathogens may cross the placenta and infect the fetus (Can cause spontaneous abortion, birth defects, premature birth)
4. Parental Route
   Not a true portal of entry
   Means by which the portal of entry can be circumvented
   Pathogens deposited directly into tissues beneath the skin or mucous membranes
   800,000 needle stick injuries reported a year by US healthcare workers (needles accidently puncture the skin)
   Estimated 50% unreported

Question 22

list the portals of exit

Answer 22

Ear (earwax)
Broken skin (blood)
Skin (flakes)
Anus (feces)
Eyes (tears)
Nose (Secretions)
Mouth (saliva, sputum)
Urethra in males (urine and semen)
Mammary glands in females (milk, secretions)
Vagina in females (blood, secretions)
Seminal vesicles (semen and lubricating secretions)

Question 23

explain the stages of disease ( be able to draw table)

Answer 23

Incubation ( pathogen enters the body and beings 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

Compare and contrast endemic, epidemic and pandemic.

Answer 25

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 contiguous 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 26

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

Answer 26

talk to clare

Question 27

Define nosocomial infection and discuss contributing factors

Answer 27

Hospital acquired infection or healthcare-associated infection

Any disease or illness that results from treatment in a hospital or healthcare setting

• Control of nosocomial infections
  – Precautions designed to reduce factors that result in disease

2 million infections per year in US (99,000 deaths)
Antibiotic resistance a growing concern

types
Exogenous
Pathogen acquired from the healthcare
environment
Endogenous
Pathogen arises from normal microbiota due
to factors within the health care setting
Iatrogenic
Literally means “doctor induced”
Results from modern medical procedures

Hand washing is the best way to reduce nosocomial infections.