Topic 10 - Principals of diseases

Question 1

What is the difference between transient and normal microbiota?

Answer 1

Transient - present for days, weeks or months

normal - permanently colonize host

Question 2

What is symbiosis?

Answer 2

The relationship between normal and microbiota and the host

Question 3

What is the definition of:

Pathology, Aetiology, Pathogenesis, Infection and disease?

Answer 3

Pathology - Study of disease
Aetiology - Study of the cause of disease
Pathogenesis - Development of disease
Infection - Colonization of the body by pathogens
Disease - Abnormal state where body doesn’t function normally

Question 4

Where are normal microbiota located?

Answer 4

Nose and throat - URT
Eyes
Mouth 
Skin
Large intestine 
Urinary and reproductive systems

Question 5

What are the different types of symbiosis?

Answer 5

Commensalism, mutualism, parasitism and opportunistic pathogens.

Question 6

What is commensalism?

Answer 6

When one benefits and the other is unaffected.

Question 7

What is mutualism?

Answer 7

When both organisms benefit

Question 8

What is parasitism?

Answer 8

When one organism benefits at the expense of the other

Question 9

What are opportunistic pathogens?

Answer 9

They are some normal microbiota which when given the opportunity thrive and cause disease.

Question 10

What is microbial antagonism?

Answer 10

It is a competition between microbes.

Question 11

What do normal microbiota do?

Answer 11

• occupy niches that pathogens
• producing acids
• producing bacteriocins

Question 12

What are probiotics?

Answer 12

Live microbes applied or ingested into the body which are intended to exert a beneficial effect.

Question 13

What are Koch’s postulates?

Answer 13

1. Same pathogen needs to be present in every disease case
2. Pathogen needs to be isolated from the diseased host and grown in pure culture
3. Pathogen from pure culture must cause disease when inoculated into a healthy, susceptible lab animal
4. The pathogen needs to be isolated from inoculated animal and must be shown to be the original organism

Question 14

What did Koch’s postulates do?

Answer 14

They helped him prove a single agent was the cause of disease and it was a break through of how people thought about disease at that time.

Question 15

Wha are the limitation to Koch’s postulates?

Answer 15

• they are used to prove cause of infectious disease
• some pathogens cause several disease conditions
• some pathogens only cause disease in humans
• cant be used for diseases linked with autoimmunity or ageing (such as cancers).

Question 16

What are the factors taken into account for infectious diseases?

Answer 16

1. symptoms: change in body function felt by patient as a result of the disease
2. sign: A change in body that can be measured or observed as a result of disease
3. syndrome: A specific group of signs and symptoms that accompany the disease

Question 17

What are communicable, contagious and noncommunicable diseases?

Answer 17

• Communicable is a disease spread from one host to another
• Contagious is a disease which is easily spread from one host to another
• Noncommunicable is a disease that is not transmitted from one host to another

Question 18

What are the differences in occurrence of diseases?

Answer 18

• Incidence: fraction of a population contracts the disease during a specific time
• Prevalence: fraction of the population have the disease at a given time
• Sporadic: a disease that occurs occasionally in a population
• Endemic: a disease which is constantly present in a population
• Epidemic: a disease acquired by many hosts in a given area in a short time
• Pandemic: worldwide epidemic
• Herd immunity: immunity in most of the population

Question 19

What are the different severity/duration categories of diseases?

Answer 19

Acute, chronic, subacute and latent

Question 20

What are acute disease?

Answer 20

Symptoms which develop rapidly

Question 21

What are chronic diseases?

Answer 21

Diseases which develop slowly

Question 22

What are subacute diseases?

Answer 22

Symptoms between acute and chronic

Question 23

What are latent diseases?

Answer 23

Disease with a period of no symptoms when the causative agent is inactive.

Question 24

What are the different disease severity?

Answer 24

Local infection - pathogens are limited to a small area of the body
Systemic infection - an infection throughout the body
Focal infection - systemic infection which began as a local infection
Sepsis - toxic inflammatory condition due to spread of microbes (mainly bacteria) from a focus infection
Bacteremia - bacteria in the blood
Septicemia - growth of bacteria in the blood
Toxemia - toxins in blood
Viremia - viruses in blood
Primary infection - acute infection which causes initial illness
Secondary infection - opportunistic infection following primary infection
Subclinical - no noticeable signs or symptoms (inapparent infection)

Question 25

What is herd immunity?

Answer 25

Immunity that occurs when enough of the population is immune to the disease to break the chain of transmission. This can be produced as a result of vaccinations.

Question 26

What makes an individual more susceptible to disease?

Answer 26

• short urethra in females = increased UTI chance
• inherited traits = sickle cell disease
• climate and weather
• fatigue
• age
• lifestyle
• chemotherapy

Question 27

What are the stages of disease?

Answer 27

1. Incubation period
2. Prodromal period
3. Period of illness
4. Period of decline
5. Period of convalescence

Question 28

What is a reservoir of infection?

Answer 28

A continual source of infection

Question 29

What are examples of reservoir infections?

Answer 29

Humans- HIV, gonorrhea or any disease that can be untreated or be inapparent and is transmissible.
Carriers have inapparent or latent disease
Animals- rabies or lyme disease which are zoonoses
some disease can be cased by non-living things (botulism and tetanus)

Question 30

What are the three methods for diseases transmission?

Answer 30

1. contact transmission
2. vehicle
3. vector

Question 31

What are examples of contact transmission?

Answer 31

• direct: close association between infected and susceptible host
• indirect: spread by fomites
• droplet: transmission via airborne droplets

Question 32

What are examples of vehicle transmission?

Answer 32

Transmission via an inanimate reservoir (food, water and air)

Question 33

What are examples of vector transmission?

Answer 33

There are 2 methods:

1. mechanical - arthropods (fleas, ticks, mosquitos) which carries pathogen
2. biological - pathogen reproduces in the vector

Question 34

What are nosocomial infections?

Answer 34

Infections which are acquired as a result of hospital stay. These affect 5-15% of all hospital patients

Question 35

What is a compromised host?

Answer 35

A persons resistance which is impaired by:
1. disease
2. therapy
3. burns
The broken skin or mucous membrane make it an easy portal of entry and a suppressed immune system makes it easier for infection to start as lymphocytes are suppressed.

Question 36

What are the principal sites of nosocomial infections?

Answer 36

UTI’s (40%), surgical site (20%), LRT infections (15%), bacteraemia transmitted primarily by IV cathetars (6%), cutaneous infections (8%) and other (11%)

Question 37

How can nosocomial diseases be prevented?

Answer 37

aseptic techniques, correct contaminated material disposal, thorough and frequent hand washing, prescription of antibiotics only when appropriate and monitoring/sampling of clinic items such as air and instrument sterility.
The most important method is washing hands.