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disease ecology and epidemiology > midterm II wobeser effects on individuals and populations > Flashcards

midterm II wobeser effects on individuals and populations Flashcards

1
Q

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

A

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)

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2
Q

what is the definition of health according to the WHO?

A

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

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3
Q

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

A

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

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4
Q

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

A

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

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5
Q

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

A

severity of disfunction?

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6
Q

does every disease have a cost?

A

yes

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7
Q

the costs of disease can be…

A

direct or indirect

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8
Q

what are examples of direct costs?

A

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

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9
Q

what are examples of indirect costs?

A

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

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10
Q

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?

A

using energy: the single common denominator of life on earth

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11
Q

how is ingested energy used?

A

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

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12
Q

what are the basic rules about energy?

A

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)

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13
Q

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

A

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

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14
Q

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

A

overgrowth of teeth in chinchilla leading to inability to eat properly

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15
Q

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

A

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

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16
Q

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

A

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

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17
Q

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

A

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

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18
Q

how is the lifetime success measured?

A

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

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19
Q

what is fitness determined by?

A

a combination of survival and fecundity

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20
Q

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

A

no, it depends on the circumstances or the context.

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21
Q

at what level does disease begin?

A

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

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22
Q

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

A

avoidance, physical barriers, innate resistance, acquired resistance

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23
Q

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

A

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)

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24
Q

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

A

intact skin, gastric pH and flow of urine

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25
Q

what is the most important component of innate disease?

A

inflammation

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26
Q

why is innate resistance a double-edged sword?

A

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

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27
Q

what are the two aspects of acquired immunity?

A

cell mediated and humoral (antibody)

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28
Q

how do we know that making antibodies is costly?

A

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

29
Q

what are the two outcomes of repair?

A

regeneration and scarring

30
Q

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

A

through inflammation, immune response, and repair and scarring

31
Q

how are primary dietary insufficiency, disease and contaminants related?

A

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

32
Q

what is a population?

A

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

33
Q

what are the important features of a population?

A

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

34
Q

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

A

no

35
Q

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

A

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)

36
Q

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

A

survival or reproduction

37
Q

how does disease affect survival?

A

by direct mortality or indirectly

38
Q

what are examples of indirect mortality?

A

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

39
Q

how does disease affect reproduction?

A

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)

40
Q

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

A

averages, proportions, rates, time, contact rate

41
Q

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

A

microparasites and macroparasites

42
Q

what are general characteristics of macroparasites?

A

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

43
Q

what are the general characteristics of a microparasite?

A

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

44
Q

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

A

susceptible animals, infected animals, and resistant animals

45
Q

what are SIR models?

A

models that model susceptible animals, infected animals and resistant animals

46
Q

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

A

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

47
Q

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

A

the disease agent

48
Q

what is R0?

A

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)

49
Q

what is R0 determined by?

A

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

50
Q

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

A

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

51
Q

what is wrong with the concept of R0?

A

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

52
Q

who was the most famous super-shedder?

A

typhoid mary

53
Q

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

A

the stewardesses

54
Q

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

A

it decreases because animals become infected/recovered and resistant

55
Q

what is Reff?

A

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

56
Q

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

A

for lack of susceptibles

57
Q

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

A

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

58
Q

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

A

larger

59
Q

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

A

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

60
Q

what is a critical community size?

A

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

61
Q

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

A

in a cattle feedlot or big of broiler barn

62
Q

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

A

multi-host species

63
Q

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

A

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

64
Q

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

A

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

65
Q

how do we manage or control disease?

A

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

66
Q

with infectious diseases we generally try to reduce_________

A

transmission so Reff is <1

67
Q

how do we reduce transmission?

A

quarantine, reduce population density, control vectors, vaccinate`

68
Q

how do we need to think about disease?

A

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

disease ecology and epidemiology (4 decks)

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