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Disease Epidemiology #2 > Population Structures and Distributions > Flashcards

Population Structures and Distributions Flashcards

1
Q

Population

A

Group of individuals of a single species in a specific area

  • look at number of individuals, spatial density, and characteristics (age, gender, others…)
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2
Q

Distribution limits

A
  • Often used in wildlife ecology
  • homeostasis occurs over a range of conditions which vary geographically
  • the physical environment limits geographic distribution of a species
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3
Q

Domestic animals distribution factors

A

both physical environment and economic factors may play a role in the distribution of animals

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4
Q

Patterns seen in distribution limits

A
  • random (most rare?)
  • regular
  • clumped or clustered (due to scarce resources)
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5
Q

Coyote distribution in Sask

A
  • measured by determining number of depredation attacks by coyotes on cattle
  • can be placed in distribution map (dark= more incidence)

**Higher coyote locations also have higher pathogens associated with coyotes

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6
Q

Beef cow distribution in Canada

A

Highest in Alberta
- then sask, manitoba, ontario, BC, Quebec, Atlantic

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7
Q

Dairy cow distribution in Canada

A

Highest in Ontario and Quebec

**where higher number of humans are

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8
Q

Infertility problem & population impact

A

Farmer noticed poor rate of fertility. Before turning them out, they were vaccinated and farmer thinks this played a role.

  • Examined data, noticed higher fertility rates originally and then decrease.
  • Farmer had rotated bulls and they found out neighbours bull had broken in with cows.

**Bull most likely introduced pathogen to herd leading to decrease in fertility. If it were vaccine, would have expected to see decrease near when vaccination occurred.

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9
Q

Hans Rosling Quote

A

Its all about populations and distributions

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10
Q

Nipah virus transmission depending on populations

A

Nipah passed on between bats, pigs, humans or Consumption of infected palm sap (when bats feed and humans ingest)

  • Transmission did not depend on human population, bat population, number of date palm sap trees
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11
Q

What did transmission of Nipah depend on?

A

Depended on consumption rates of date sap oil and presence of bat hunter in the village

**Each 10% increase in the proportion of households reporting regular consumption of raw date sap increased odds of being a “case village” by 6.4x

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12
Q

Epidemiological Triad

A
  • Host
  • Agent
  • Environment

**Combination can lead to disease

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13
Q

Does population structure and social organization affect parasite transmission and prevalence?

A

Yes

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14
Q

Social systems of animal populations

A
  • Exhibit structure at several levels (individuals, group, and within the group)
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15
Q

Components of individual level that can impact animal populations

A
  • age
  • sex
  • reproductive rate
  • relatedness
  • position in dominance hierarchy
  • social interactions
  • patterns of space use
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16
Q

Components of group level that can impact animal populations

A

**looking at heard, farm, etc.

  • group sizes vary within and among species
  • wildlife (solitary; only interaction is mating)
    monogamous pairing
    socially complex groups
  • huge aggregations of individuals
  • economics and structure of agriculture industry or urban environment
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17
Q

Components within a group that can impact animal populations

A
  • sex, age, social status of individual
  • season
  • super-spreaders

**All of these affect the number and types of pathogens that they will come in contact with and therefore the exposure and transmission rates

18
Q

What effects transmission of a parasite among groups?

A
  • group size
  • composition
  • territoriality
  • levels of inter-group movement and contact
19
Q

Community pastures

A
  • government buys land, restores the environment and community can pay to have cows stay there during summer (summer camp!).
  • can also pay to use government cows for breeding

**Creates a population. If a pathogen goes through, it can be spread very quickly all over the area when animals return to their own farms. (Huge risk factor)

20
Q

Gender distribution (within group)

A

several diseases show a bias towards a particular gender

Mating behaviour:
- polygamy (1 male, multiple females)= COMMON
- variance in mating success (socially dominant males mate more often)
- increase in STD’s

21
Q

Bovine TB and CWD

A

**Gender distribution of pathogens within a group

Deer show higher prevalence in males:
- larger animals more susceptible to vectors
- sex related differences in home range and physiology/behaviour (higher stress for males in breeding season; hormones affect immune system)

22
Q

Age distributions (within a group)

A

Age affects disease prevalence. Different diseases happen at different ages

  • If a pathogen does not kill host, prevalence of disease will often increase with age (TB, CWD, Johne’s disease)
  • if hosts recover and get immunity, juveniles may have higher prevalence
  • infnats may be initially protected by maternal immunity and become susceptible when passive immunity wanes
  • if antibody titers persist, seroprevalence is also likely to increase with age
23
Q

Social dominance (within a group)

A
  • complicated by breeding behaviour, rank stability, and coping mechanisms for subordinates
  • can affect exposure rates as well as stress levels
  • chronic stress can impair the immune system
24
Q

Super spreaders (within a group)

A

-Not all hosts are equally susceptible and infectious (but hard to identify; may need social networks to determine)

  • a few individuals often infect a large number of other animals. So focusing control on them will be most effective way to control disease spread
25
Q

20/80 rule

A

20% of individuals within a population are thought to contribute at least 80% to the transmission potential of a pathogen

*R0 is important but it is an average and there are lots of variations between individuals

26
Q

SARS outbreak and 20/80 rule

A

77 patients
- 66 did not infect anyone
- 7 infect 3 or less
- 4 super spreaders infect 8 or more

27
Q

What makes a superspreader?

A

Biological, behavioural, and social factors

  • host (physiological, behavioural, immunological)
  • pathogen (virulence, coinfection)
  • environment (crowding, misdiagnosis, movement of infected hosts, ventilation)
28
Q

Intergroup factors

A
  • Territoriality
  • group size and population density
  • economic organization of agricultural industry
28
Q

Territorial (intergroup)

A
  • aggressive encounters increase exposure
  • defensive behaviours energetically costly and increase stress
  • biting and scratching= transmission mechanisms
  • can also reduce transmission by reducing contact between individuals and groups
29
Q

Group size and population density (intergroup)

A

** Affects CONTACT rate

  • disease maintenance and transmission enhanced at higher densities
  • affects industry economics and structure

(can be altered depending on urban habitats, size of home ranges, movements/distance moved, barriers to dispersal, habitat needs)

30
Q

Economic organization of industry (intergroup)

A

Structure and economics of agriculture may have major impact on contact rates and disease transmission
- herd sizes
- herd densities and inter herd contact
- animal movement
- inter-species mixing and within-species mixing
- cross border movement of animals

31
Q

Beef industry

A
  • concentrated in southern Alberta (lots of small herds, and then feedlot sector)
  • industry structure results in major increased contact between animals, increasing chance of disease spread.

Ex. 2 major beef processors. For farmers to get paid, must send cows to auction because farmers cant negotiate with major beef processors because they can always get beef.

32
Q

Diagnosis= probabilities and population distributions

A

diagnosing an individual will require putting it into its perspective population distribution. Leads to knowing what the risk factors or tendencies will be for the individual

33
Q

Elements of disease

A
  1. disease or target disorder (objective of the diagnostic process)
  2. illness (cluster of symptoms and signs)
  3. predicament (environment, client limitations, “where the animal is situated”)
34
Q

Pattern recognition: Clinical diagnostic strategy

A
  • Pattern recognition- instantaneous realization that the patients presentation is similar to previously learned patten of disease (visual, auditory, or odor)
35
Q

Arborization strategy: Clinical diagnostic strategy

A
  • flow chart of a large number of potential, preset pathways of diagnostic inquiries
  • must be logical and include all relevant causes
  • good for discrete and accurate data
  • useful with triage cases (delegating to others)
  • may be poor at handling atypical cases but good for uncommon conditions
  • not always efficient
36
Q

Exhaustive method- Clinical diagnostic strategy

A
  • ” Go do a complete history and physical”
  • painstaking, invarient search for all medical facts about individual. Then have to sift through all data.
  • can also include lab component
  • can be useful in complex cases, however usually inefficient and often abandoned with experience
  • study shows exhaustive testing did not improve anything compared to other methods
37
Q

Hypothetico-deductive strategy- Clinical diagnostic strategy

A
  • Used by all clinicians all the time; formulation of a short list of potential diagnoses or actions based on early clues
    » come from pattern recognition/explanatory ideas that tie biology to signs/symptoms, population distributions and risk factors
38
Q

What other diagnostic maneuvers are used to shorten list of potential hypotheses?

A
  • history, physical exam, x-rays, lab tests
39
Q

Clinicians hypothesis study

A
  • first hypothesis in first 28s
  • correct hypothesis ~6mins
  • correct 75% of time
  • avg 5.5 hypotheses generated for each case
  • usually working list with rule outs of 3-4
  • most clinicians will support their hypothesis by seeking evidence rather than ruling out the hypotheses

Disease Epidemiology #2 (11 decks)

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