midterm II wobeser effects on individuals and populations

Question 1

what is the definition of disease for: human, pet animals, food animals, and free-living animals?

Answer 1

for humans and pets, disease is non-infectious conditions that reduce quality of life for the individual (we don’t usually worry about infectious diseases, and then overreact); for food animals, disease are conditions that reduce the productivity and this is a “group” rather than “individual” view; in free-living animals, disease are conditions that affect the population rather than the individual (these usually deal with survival or reproduction)

Question 2

what is the definition of health according to the WHO?

Answer 2

it is a state of complete, physical, mental and social well-being and not merely the absence of disease or infirmity

Question 3

what is a definition of disease that encompasses the varied views of disease for different groups?

Answer 3

any impairment that interferes with or modifies the performance of normal functions; infection is not synonymous with diesase

Question 4

what does the definition of disease stated in class not specify?

Answer 4

the type of function that is impaired or the type of agent or factor that causes the dysfunction

Question 5

On a graded scale, what is inversely proportional with health?

Answer 5

severity of disfunction?

Question 6

does every disease have a cost?

Answer 6

yes

Question 7

the costs of disease can be…

Answer 7

direct or indirect

Question 8

what are examples of direct costs?

Answer 8

mortality; injuries that have to be repaired, injuries that result in less efficiency; direct loss of resources (e.g. tapeworm stealing nutrients); loss of reproduction

Question 9

what are examples of indirect costs?

Answer 9

avoidance (the cost of avoiding disease), resistance (against disease–costs to build resistance), increased vulnerability to harmful factors

Question 10

how can we measure the costs, or compare the cost of mounting an immune reaction or producing a suppurative response or repairing an epithelial ulcer?

Answer 10

using energy: the single common denominator of life on earth

Question 11

how is ingested energy used?

Answer 11

it is assimilated, some is lost and then it is dedicated to respiration (maintenance, thermoregulation, defence), production (growth, reproduction), and storage

Question 12

what are the basic rules about energy?

Answer 12

an animal cannot use more energy than it can assimilate + the stores it has available (can’t overspend)
if an animal uses more energy for one purpose, there is less available for other purposes (i.e. limited supply)

Question 13

in a coyote with sarcoptic mange, describe the effects on energy ingested and the use of that energy

Answer 13

the ingested energy was reduced because the animal was preoccupied with the disease; the respiration (maintenance, thermoregulation and defense) energy requirement increased because there was decreased hair to keep the animal warm in the winter and to mount defenses against pathogens that enter wounds; the production (growth reproduction) energy is suspended and pups stop growing and adults stop reproducing; the storage energy is depleted as the animal draws on these stores

Question 14

what is an example of disease that can result in decreased energy ingested?

Answer 14

overgrowth of teeth in chinchilla leading to inability to eat properly

Question 15

what is an example of disease that can result in decreased assimilation?

Answer 15

Johne’s disease in cow causing a thickened gut and a malabsorption

Question 16

what is the general concept of how energy is partitioned in an animal?

Answer 16

animals have to make choices among the activities that require energy and the goal is to make the trade-offs that will lead to the greatest life-time success; these choices are genetically determined

Question 17

what are some examples of “choices” that cost energy?

Answer 17

grow or reproduce, immune response or reproduce, run away or resist

Question 18

how is the lifetime success measured?

Answer 18

fitness (the relative success of the individual in having its genotype passed on to succeeding generations)

Question 19

what is fitness determined by?

Answer 19

a combination of survival and fecundity

Question 20

is there an absolute role as to how energy should be apportioned?

Answer 20

no, it depends on the circumstances or the context.

Question 21

at what level does disease begin?

Answer 21

the cellular level: by interference with the cell’s energy or resource supply or by damage to the cell membrane

Question 22

how do animals prevent or reduce cell injury (resistance?)

Answer 22

avoidance, physical barriers, innate resistance, acquired resistance

Question 23

what is an example of avoidance with regards to resisting disease?

Answer 23

sheep graze on less nutritious grass if it has feces IF they are in a good nutritional state. (sheep in a poor nutritional state don’t avoid the disease)

Question 24

what are examples of physical barriers that animals use to resist disease?

Answer 24

intact skin, gastric pH and flow of urine

Question 25

what is the most important component of innate disease?

Answer 25

inflammation

Question 26

why is innate resistance a double-edged sword?

Answer 26

because inflammation can often kill an animal due to fluid buildup, toxic substances released, fibrotic tissue that forms etc. e.g. a feedlot steer that died of fibrous pneumonia died of the immune response "inflammation is simultaneously the most important and useful of our host defence mechanisms and the most common means by which tissues become injured. more animals have died of inflammatory disease than all other causes combined, yet without an adequate inflammatory response, none of us would be living

Question 27

what are the two aspects of acquired immunity?

Answer 27

cell mediated and humoral (antibody)

Question 28

how do we know that making antibodies is costly?

Answer 28

cost sparrows 1/2 an egg to make one type of antibody

Question 29

what are the two outcomes of repair?

Answer 29

regeneration and scarring

Question 30

how does most of the actual injury to a body due to an agent result?

Answer 30

through inflammation, immune response, and repair and scarring

Question 31

how are primary dietary insufficiency, disease and contaminants related?

Answer 31

they can cause inadequate intake, disease can steal resources for resistance and repair causing malnutrition, or can cause reduced mobility, anorexia or impaired nutrition, leading to malnutrition, which can cause impaired avoidance, reduced detoxification, reduced gastric acidity, reduced immunity, impaired epithelial integrity and impaired repair. this leads to reduced defences (contaminants can also cause this); reduced defences leads to increased exposure and reduced resistance that can lead back to disease

Question 32

what is a population?

Answer 32

a group of individuals of the same species that live together in an area of sufficient size to permit normal dispersal and or immigration behaviour and in which numerical changes are largely determined by birth or death processes

Question 33

what are the important features of a population?

Answer 33

size, rate of contact, spatial distribution, sex and age composition, rate of turnover (replacement--susceptibles often come in by birth)

Question 34

are the effects of most diseases uniformly distributed in a population?

Answer 34

no

Question 35

if a population had intestinal parasites, how would you expect the parasites to be distributed?

Answer 35

a minority of the individuals would have the majority of the parasites; most animals would have few parasites; the ones with many parasites are likely to do most of the transmision (supershedders)

Question 36

effects of disease at the popultion level act by influencing _______ or __________

Answer 36

survival or reproduction

Question 37

how does disease affect survival?

Answer 37

by direct mortality or indirectly

Question 38

what are examples of indirect mortality?

Answer 38

increased susceptibility to predation (or culling), increased susceptibility to other diseases, increased susceptibility to physical factors

Question 39

how does disease affect reproduction?

Answer 39

injury to reproductive organs, injury to the fetus, interference with reproductive behaviour (e.g. appearance of the male--hemorrages on airsac, less attractive to male)

Question 40

at the individual level we deal with yes/no questions, but when we talk at the population level we talk about________

Answer 40

averages, proportions, rates, time, contact rate

Question 41

what is an ecological way to classify disease agents (two groups)?

Answer 41

microparasites and macroparasites

Question 42

what are general characteristics of macroparasites?

Answer 42

they are larger, their generation time is longer, they have little or no reproduction within the host, they are persistent, reinfection is common, chronic and usually sublethal, immunity depends on presence of infection---don't have long term immunity against them

Question 43

what are the general characteristics of a microparasite?

Answer 43

they are smaller, the generation time is shorter, they have a high reproduction rate within the host, the duration of infection is shorter, the disease is often short-lived and severe, the immunity to reinfection is often long-lasting and reinfection is uncommon

Question 44

In a population, there are three types of individuals with respect to any disease caused by a microparasite

Answer 44

susceptible animals, infected animals, and resistant animals

Question 45

what are SIR models?

Answer 45

models that model susceptible animals, infected animals and resistant animals

Question 46

The course of infection with a microparasite in an individual follows this pattern:

Answer 46

susceptible--->infected--->recovered and resistant or remains chronically infected or dies at some point in the infected period, this animal will become infectious

Question 47

the time interval from susceptible to recovered and the length of time the animal is infectious are features of?

Answer 47

the disease agent

Question 48

what is R0?

Answer 48

the basic reproductive number (rate) of a disease it is the average number of secondary infections that arise from introduction of one infected individual into a fully susceptible population (also called average transmission ratio)

Question 49

what is R0 determined by?

Answer 49

frequency of contacts, proportion of contacts that result in transmission (proportion of contacts with S individuals and how easily the disease spreads from one animal to another are important factors that determine this

Question 50

what must R0 be for a disease to invade a population?

Answer 50

equal or greater than 1 (on average each infected individual must infect at least one new individual or disease will not be established)

Question 51

what is wrong with the concept of R0?

Answer 51

in many diseases, most of the transmission results from a small number of individuals that are super spreaders/shedders

Question 52

who was the most famous super-shedder?

Answer 52

typhoid mary

Question 53

what is an example of a group of super shedders in the SARS epidemic?

Answer 53

the stewardesses

Question 54

as a disease spreads within a population, what happens to the proportion of contacts that are with susceptible animals?

Answer 54

it decreases because animals become infected/recovered and resistant

Question 55

what is Reff?

Answer 55

it is the effective reproductive number; it is used when the whole population is not made up of completely susceptible individuals

Question 56

in a small population, why does a disease die out?

Answer 56

for lack of susceptibles

Question 57

does a disease die out when all the susceptibles are gone?

Answer 57

no, there are still susceptibles left but the Reff has fallen below 1.

Question 58

in what population can a disease persist for more generations? (larger or smaller)

Answer 58

larger

Question 59

how could a disease persist in a population (factors that increase likelihood)

Answer 59

large population, continual addition of susceptibles, more than one host species, chronically infected individuals, survival of the agent outside the host, a population divided into many discrete units with limited contact between units

Question 60

what is a critical community size?

Answer 60

it is the size of a population that is required for a disease to persist until new susceptibles enter the poputlion

Question 61

in what situation would susceptibles be added at an accelerated rate in a way that allows disease to persist?

Answer 61

in a cattle feedlot or big of broiler barn

Question 62

most of the most serious disease on a global level are what?

Answer 62

multi-host species

Question 63

in a multihost species, what is it critical to define?

Answer 63

who is the maintenance host, who is the spillover host and who is the dead end host

Question 64

what is wrong about looking at a population as a randomly mixed group of individuals?

Answer 64

they are often organized into smaller groups with limited exchange (e.g. farms in a region)

Question 65

how do we manage or control disease?

Answer 65

reduce the exposure to the agent or risk factor, increase the resistance (reduce the effect)

Question 66

with infectious diseases we generally try to reduce_________

Answer 66

transmission so Reff is <1

Question 67

how do we reduce transmission?

Answer 67

quarantine, reduce population density, control vectors, vaccinate`

Question 68

how do we need to think about disease?

Answer 68

in terms of cost, context (interactions), fitness, effects at the population level....long term not short term