virulence and infectivity

Question 1

disease

Answer 1

a condition that impairs normal tissue function

Question 2

how much disease is present is reliant on..

Answer 2

population growth and food security (and affordability)

Question 3

types of diseases

Answer 3

genetic and metabolic; diseases of aging; infectious

Question 4

genetic of metabolic disease

Answer 4

e.g. CF- is due to a specific genotype that results in impaired transport of chloride ions across membrane

Question 5

diseases of aging

Answer 5

e.g. atherosclerosis- typically becomes a problem later in life after plaques of cholesterol have built up and partially block arteries

Question 6

infectious disease

Answer 6

e.g. measles is an infectious disease because it occurs when an individuals contracts an outside agent

Question 7

infection is

Answer 7

invasion

Question 8

why is infection and disease not the same

Answer 8

some pathogens can infect an organism but not yet cause disease- disease results only if and when, as a consequence of invasion and growth of pathogen, tissue function is impaired

Question 9

a pathogen is

Answer 9

an organism capable of causing disease- a disease causing agent in a susceptible host

Question 10

true pathogen

Answer 10

if it is on or within the host, it will cause disease

Question 11

opportunistic pathogen

Answer 11

potentially infectious agents that rarely cause disease in individuals with healthy immune systems .e.g Candidia

Question 12

4 outcomes of microbe/host interaction

Answer 12

commensalism, colonisation, latency and disease

Question 13

pathogenicity is..

Answer 13

a discontinuous variable- there i or is not pathogenicity

Question 14

virulence is just

Answer 14

one of the number of possible outcomes of a host-microbe interaction

Question 15

virulence is a …. variable

Answer 15

continous–> the amount of damage or disease that manifests

Question 16

which disease effects the largest area

Answer 16

rice blast- enough rice to damage 60 mill people annually

Question 17

what is ID50

Answer 17

median infective dose

Question 18

median infective dosea

Answer 18

the amount of pathogenic microorganism that will produce demonstrable infection in 50% of the test subject

Question 19

LD50

Answer 19

median lethal dose

Question 20

median lethal dose

Answer 20

the quantity of an agent that will kill 50% of the test subjects

Question 21

morbidity rare

Answer 21

incidence of a disease across a population and or/geographic location during a single year

Question 22

what influences ID50 and LD50

Answer 22

host: age, genetics, environment, nutrition, stress

immunological status

Route of infection- inhalation, skin, ingestion (anthrax)

Question 23

virulence factor

Answer 23

traditionally used to describe a microbial characteristic- intrinsic microbial property that distinguishes pathogenic from non-pathogenic

Question 24

Kochs postulates

Answer 24

1) Gene under investigation should ebe associated with pathogenic members of a genus or pathogenic strains of a species. Gene should be found in all pathogenic strains of the genus or species but absent from non pathogenic strains
2) The gene, which causes virulence, must be expressed during infection
3) Specific inactivation of the gene associated with the suspected virulence trait should lead to a measurable loss in pathogenicity or virulence- virulence must be less in inactivated genes
4) Reversion or allelic replacement of the mutated gene should lead to restoration of pathogenicity. i.e. reintroduction of the gene into the microbe should restore virulence in the animal model.

Question 25

classic virulence factor

Answer 25

toxins e.g. anthrax - toxins encoded on a plasmid and removal results in attenuation

Question 26

limitation of virulence factor concept

Answer 26

diff to apply to microbes who’s pathogenicity is limited mostly to immunocompromised hosts- such as C.albicans and asperigillus

Question 27

biofilms and polymicrobial infections

Answer 27

planktonic bacteria are vulnerable to several anti-microbial phenomena- liquid phase and surface of biofilm

Question 28

in a biofilm

Answer 28

the physical nature of the microbial biofilm and the surface to which it is attached protects the bacteria

Question 29

epidemiology

Answer 29

effects of pathogens on populations where and when disease occurs

Question 30

incidence

Answer 30

the number of new cases of disease in a given area or population

Question 31

prevalence

Answer 31

is the total number - new and already existing

Question 32

incidence and prevalence are typically expressed as

Answer 32

ratios of cases divided by number of people at risk

Question 33

nosocomial infections

Answer 33

acquired by patients or health workers from the health environment (e.g. doctors, dentist, care home)

Question 34

pathogenicity is… and the host is..

Answer 34

discontinuous and dependent

Question 35

how can virulence be deterined

Answer 35

experimentally

Question 36

what is used to identify virulence factors

Answer 36

genetics via Koch’s molecular postulates

Question 37

commensalism

Answer 37

an association between two organisms in which one benefits and the other derives neither benefit nor harm.