EPIDEMIC CURVES & DETERMINANTS OF DISEASE

Question 1

Latent period

Answer 1

Latent period = microbe is replicating but not yet enough for the host to become infectious.

Question 2

Incubation period

Answer 2

Incubation period = microbe is replicating but not symptomatic yet. Does not always correlate with the latent period.

Question 3

Infectious

Answer 3

Infectious- disease caused by the invasion and multiplication of a living agent in/on a host

Question 4

Infestation-

Answer 4

Infestation- invasion, but not multiplication of an organism in/on a host (fleas/ticks, sometimes parasites)

Question 5

Contagious

Answer 5

Contagious- disease transmissable from one human/animal to another via direct or airborne routes.

Isolation is a way that you could control contagious diseases

Question 6

Communicable-

Answer 6

Communicable- disease caused by an agent capable of transmission by direct, airborne, or indirect routes from an infected person, animal, plant or a contaminated inanimate reservoir.

A disease can be communicable but not contagious. When a disease is communicable, you have to worry about vector control, enviornmental etc

Question 7

Epidemic Curves

Answer 7

Represent the number of new cases of disease, over time

Are simple to make and interpret

Can tell you:
– Most probable source of the outbreak
– If the pathogen is contagious
– If the outbreak is ending – or will continue
– Incubation period of the pathogen (sometimes)

– About outliers

Question 8

What separates each wave?

What type of a curve is this?

Answer 8

Incubation Period

Propagative Curve- as the days increase, the amount of new cases increases- it is contagious

Question 9

What kind of curve is this?

Answer 9

Epidemic Curve:

Common Source Single Point Exposure- steep rise, comes to a peak and then falls off

only one incubation period

• All animals are exposed at once
• All are exposed to the same source of infection
• Not contagious
• Can determine the minimum, average, and maximum incubation time

Question 10

What kind of curve is this?

Answer 10

Common Source w/ Intermittent Exposure

Animals are exposed at different times

Exposed to the same source

Incubation period is NOT clearly shown

Question 11

What determines the shape of the epidemological curve?

Answer 11

Depends on several factors:

Host

– Immunity or other resistance to disease

– Direct transmission

Agent
– Infectiousness of agent

– Latent and incubation periods

– Duration of infectivity

Environment

Question 12

Endemic Stability

Answer 12

– Endemic (enzootic) vs. epidemic (epizootic)

A situation in which all factors influencing disease are relatively stable, resulting in little fluctuation in disease incidence over time

– New cases occur at a regular, usually low, level

– Young individuals may enter the population
– Old individuals die or are removed

Question 13

DETERMINANTS

Answer 13

Factors that help DETERMINE the probability, distribution, or severity of a disease in an animal or population of animals.

Host susceptibility is one kind of determinant – but not the only one!

these are important because:

• id’s animals at risk
• disease prevention
• aid to differential dx

Question 14

Primary Determinants

Answer 14

Primary = a MAJOR contributing factor, usually a NECESSARY one

It has to be present for the disease to occur

Question 15

Secondary Determinants

Answer 15

Secondary = factors that make the disease more or less LIKELY; predisposing or enabling factors

Question 16

Intrinsic Determinats

Answer 16

Intrinsic = determinants that are internal to the animal (age, breed, sex, etc.)

Question 17

Extrinsic Determinants

Answer 17

Extrinsic = determinants that are external to the animal (housing, medical treatment, etc.)

Question 18

PRIMARY Determinants

Answer 18

Primary determinants MUST ALWAYS be there in order for disease to occur

– AKA “necessary causes” in Rothman’s model of diseases (later)

Primary determinants satisfy the “gotta have it” test!

– Everything else is “secondary”, just a “component cause”

i.e. for anthrax- you have to have the spores and you have to have the suceptible cattle

Question 19

Mutations can include

Answer 19

Mutations can include
– Increased infectivity within typical hosts
– Ability to infect new species / populations of hosts – Acquisition of new toxins
– Immune system evasion

Question 20

Antimicrobial resistance can be obtained

Answer 20

Antimicrobial resistance can be obtained either de novo, through mutation, or via lateral transfer from another organism

Question 21

Genotype

Answer 21

Genotype = a term describing the DNA sequence, or “type”, of an individual

Question 22

Genetic diseases are ENTIRELY determined by

Answer 22

Genetic diseases are ENTIRELY determined by genotype

Question 23

What determines genetic susceptibilties?

Answer 23

Genetic susceptibilities are PARTIALLY determined by genotype and partially by other factors

Question 24

Herd Immunity

Answer 24

The idea that infectious diseases can be contained if the population’s resistance to infection is high enough

– Does NOT protect individuals

– Some non-immune individuals will probably

become infected…

– Many others will be protected, indirectly, by the immunity of their herd-mates

üCan be applied to populations of people as well as populations of animals!

Question 26

Is it easier if the latent and the incubation period? Which one is more important?

Answer 26

Latent period is more important and yes it is easier

Question 27

What kind of determinate do you want to target for prevention?

Answer 27

Primary extrinsic factors