Pathogenicity, transmission and epidemiology

Question 1

What is an infectious disease?

Answer 1

Illness caused by microbes ie. bacteria, fungi, virus, Protozoa

Question 2

What is a communicable disease?

Answer 2

Disease spread from person to person

Question 3

What is a contagious disease?

Answer 3

Subset of extremely communicable diseases, transmitted by physical contact, casual contact with their secretions or objects touched by them or airborne

Question 4

What are carriers?

Answer 4

Infected but asymptotic, will be infectious forever

Question 5

What is a local infection?

Answer 5

In a single spot on the body, local to that area ie. staphylococcal impetigo infection

Question 6

What is a systemic infection?

Answer 6

Affects the whole body

Question 7

What is an acute disease?

Answer 7

Really nasty for a short amount of time and then either recover or die ie. influenza and mumps

Question 8

What is chronic disease?

Answer 8

Slow onset and long duration ie. leprosy and syphilis

Question 9

What is latent (dormant) infection?

Answer 9

Infected but not currently sick ie. tuberculosis, herpes simplex virus

Question 10

What is a pathogen?

Answer 10

Pathogen is a microbe that makes you sick, it’s not part of the normal flora

Question 11

Can normal flora act like a pathogen?

Answer 11

Yes, when it ‘moves house’

Question 12

What is pathogenicity?

Answer 12

A measure of how easily a bug can make you sick

Question 13

What are opportunistic infections?

Answer 13

An infection caused by pathogens that take advantage of an opportunity not normally available ie. host with a weakened immune system

Question 14

What are the three factors of pathogenicity/virulence?

Answer 14

• Transmission
• Inflammation
• Toxigenicity

Question 15

Explain transmission

Answer 15

Infect the host and protect itself against the hosts defences

Question 16

Explain inflammation

Answer 16

Invade and multiply in the tissue

Question 17

Explain toxigenicity

Answer 17

Cause damage or destroy tissue

Question 18

How is pathogenicity measured?

Answer 18

By the number of bugs required to cause disease

Question 19

What is ID50?

Answer 19

Infectious dose 50%, the number of bugs required to cause disease in half the hosts

Question 20

What does LD50 stand for?

Answer 20

Lethal dose 50%

Question 21

Is a higher or lower LD50 said to be more virulent?

Answer 21

Lower as they require less bugs to cause death or disease

Question 22

What is Ro (R-naught)?

Answer 22

The measure of transmissibility, the number of people that one sick person will infect (on average)

Question 23

What is a good way to prevent infectious disease?

Answer 23

Interrupting the chain of disease

Question 24

What are the modes of transmission? (8 points)

Answer 24

• respiratory droplets
• dust
• contaminated water
• contaminated food
• contact with contaminated objects
• infection of contaminated soil eg. Standing on a nail
• arthropod bites eg. Insects
• contact with animals

Question 25

What are the portals of exit? (6 points)

Answer 25

- coughing and sneezing - insect bites - skin cells and open lesions - urine - faeces - blood

Question 26

What are the two routes of transmission?

Answer 26

- human to human | - non human to human

Question 27

Human to human transmission? (4 points)

Answer 27

- direct contact - no direct contact - trans placental - blood borne

Question 28

Non human to human transmission? (5 points)

Answer 28

- soil - water - food - animal/insect - Fomites (object)

Question 29

What are virulence factors?

Answer 29

Properties that enable a microorganism to establish itself on or within a host and enhance its potential to cause disease

Question 30

What are 3 types of virulence factors?

Answer 30

- infectivity and morphological (shape) properties - invasion - toxin production

Question 31

What are the infectivity and morphological properties?

Answer 31

- fimbriae - Pili - capsule - biofilm

Question 32

What are fimbriae?

Answer 32

Small, finger like projections (hairs) around the outside of bacterial cells which helps it stick and be infectious

Question 33

What are pili?

Answer 33

Way to horizontally transmit genetic material between bacteria (sex pilus) ie. pass on information for antibiotic resistance etc

Question 34

What is a capsule?

Answer 34

A sticky like substance around the outside of a bacterial cell which makes it hard for phagocytosis to occur, makes it hard for cell wall synthesis or protein synthesis to occur.

Question 35

What is biofilm?

Answer 35

A thin but robust layer of mucilage adhering to a solid surface and containing a community of bacteria and other microorganisms

Question 36

What are the 3 enzymes that help invasion?

Answer 36

- collagenase (breaks down collagen) - hyaluronidase (breaks down hyaluronic acid) - coagulase (accelerates clotting)

Question 37

What are the 2 types of toxin production?

Answer 37

- exotoxins - secreted by some living pathogens - endotoxin - a toxin present inside the cell wall of a gram negative bacteria which is released when on cell lysis or death of the bacteria

Question 38

What is the chain of infection? (6 points)

Answer 38

- causative agent - environment (reservoir of infection) - modes of transmission - portal of exit - portal of entry - susceptible host

Question 39

What is epidemiology?

Answer 39

The study of the frequency and distribution of diseases and the factors that contribute to their spread

Question 40

Endemic meaning?

Answer 40

Diseases present in the population in particular limited geographical areas

Question 41

Epidemic meaning?

Answer 41

Diseases that show a high incidence in a wider area, usually developing from an endemic focus

Question 42

Pandemic meaning?

Answer 42

Diseases distributed worldwide or over a very wide area, crossing international borders

Question 43

Sporadic disease meaning?

Answer 43

Neither endemic or epidemic, occurs only occasionally

Question 44

Reservoir of infection meaning?

Answer 44

Site where the pathogen can multiply or survive until it is transferred to its host

Question 45

Common source epidemic meaning?

Answer 45

Results from an infection of a large number of people from a common contaminated source such as food or water

Question 46

Host to host epidemic meaning?

Answer 46

Shows a relatively slow progression and a gradual decline ie. influenza

Question 47

Nosocomial or healthcare acquired infections (HAI) meaning?

Answer 47

Diseases that are contracted in a medical facility

Question 48

Zoonosis meaning?

Answer 48

Caused by pathogens that reproduce in both humans and animals

Question 49

The 4 stages of an infectious disease?

Answer 49

- incubation - prodrome (not yet sick but feel it coming) - specific illness - recovery or death

Question 50

Epidemiological case study involves? (5 points)

Answer 50

- history - transmission and contacts - symptoms/pathogenicity - treatment - control