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BIOL 208 > Disease Ecology > Flashcards

Disease Ecology Flashcards

1
Q

What is considered a disease?

A

an “atypical” condition in a living organism that causes some sort of a physiological impairment

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2
Q

what are non-infectious diseases caused by?

A

environmental toxins, genetics, etc.

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3
Q

what are infectious diseases caused by?

A

pathogens - include viruses, bacteria, worms, fungi, protists

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4
Q

How are pathogens transmitted?

A
  • bodily fluids/feces
  • soil/water
  • vector boune
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5
Q

Zoonotic diseases

A

diseases transmitted from animals to humans

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6
Q

What is disease ecology?

A

the ecological study of host-pathogen interactions within the context of their environment and evolution

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7
Q

Examples of Zoonotic diseases?

A
  • Nipah Virus (small fruit bats), a RNA virus
  • Lyme disease (a bacterial infection, transmitted via deer ticks)
  • malaria (caused by single-celled protists, transmitted to humans via mosquito)
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8
Q

Two goals of disease ecology

A
  1. to understand pathogen transmission and spread over time and space
  2. the impacts on host populations
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9
Q

Virulence

A

a pathogens ability to damage the host

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10
Q

Define Direct Transmission

A

direct contact between hosts, via air, water, soil or other surfaces

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11
Q

Define Indirect Transmission

A

indirect transfer of the infectious agent, e.g., by airborne, formites, animal vectors

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12
Q

Horizontal Transmission

A

among individuals of the same generation

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13
Q

Vertical Transmission

A

from mother (parent) to child (offspring) before or during birth

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14
Q

Replication of Viruses

A
  1. virus binds to and enters cells
  2. the virus delivers its genome to a site where it can produce new copies of viral proteins and RNA
  3. viral proteins and RNA assemble into new viral particles, and exit the host cell; via the cell wall bursting (aka ‘lysing’)
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15
Q

Is COVID-19 vertically or horizontally transmitted?

A

mostly horizontally transmitted
- the virus enters the respiratory system via the human mouth or nose and then spreads from there
- vertical transmission is rare

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16
Q

Does Pathogen transmission vary with Host Density?

A
  • transmission of a pathogen increases (linearly or non-linearly) with host density
  • the chance that an individual because infected by a pathogen is proportional to the number of possible hosts
  • as a consequence, there exists a threshold density of hosts below which the pathogen cannot persist
  • threshold host density (Nt) - minimum density of hosts required to sustain a disease within a population
17
Q

Density-dependent Transmission

A

can regulate host populations (i.e., reduce and hold them to a lower density than without the pathogen present) in the absence of any other density-dependent factors influencing host abundance

18
Q

Frequency-dependent Transmission

A
  • transmission that is relatively unaffected by host density
  • the per capita rate at which a susceptible individual becomes infected increases with the fraction of the host population that is infectious but does not increase with host density
  • as a result, there is no threshold density for pathogens
19
Q

Endemic

A

constant presence but relatively low spread
- e.g., malaria in African Regions/ SE Asia

20
Q

Epidemic

A

sudden increase (high spread) in certain regions
- e.g., Lyme disease

21
Q

Pandemic

A

global epidemic
- e.g., swine flu (2009). COVID-19

22
Q

R0 - the basic reproduction rate of a pathogen

A
  • describes the initial growth of a pathogen in a previously unexposed host population
23
Q

How is Pathogen success measured?

A

in terms of their host behaviour and pathogen traits

24
Q

R0 interpretation of a disease and under what assumptions?

A

average number of people that will be infected by a person with a disease under the following assumptions:
- in a naive population
- everyone is susceptible in that population
- w/o transmission interventions (e.g., vaccinations)

25
Q

How does R0 vary?

A
  • spatially (from region to region)
  • temporally (over time)
  • based on model used
26
Q

How do we slow a disease?

A
  1. behavioural change
  2. herd immunity
27
Q

Isolation vs. Quarantine

A
  • isolation is separating sick individuals from healthy individuals
  • quarantine is separating individuals who have been exposed to the illness, even is they are not presenting any symptoms of the disease
28
Q

What is Herd Immunity?

A

Herd immunity threshold (H): minimum percent of population that needs to be immunized to reach herd immunity

29
Q

Relationship between R0 and herd immunity thresholds ?

A

highly contagious pathogens have higher herd immunity thresholds because they spread fast

29
Q

When does Herd Immunity Occur?

A

when immunity rates are high enough that the population growth rate (r) of the pathogen is negative and may go extinct

29
Q

Host-pathogen evolution

A

parasites and hosts frequently evolve in response to one another and to their changing environments

29
Q

Exceptions for Vaccinations?

A
  • babies cannot be vaccinated until a certain age
  • some individuals are allergic to components of certain vaccines, have an abnormal autoimmune response
30
Q

Why do parasites harm their host, given that they depend on their hosts for their own transmission?

A
  • parasites should evolve to become benign and prolong the lives of their hosts
  • yet, many parasites cause substantial harm (e.g., parasite replication, damages host tissues and consumes host resources)
31
Q

What is a possible explanation for Virulence?

A
  • parasites that replicate too slowly will not produce sufficient transmission stages
  • parasites that replicate too quickly will kill their host before they can transmit
  • selection may favour pathogens with intermediate levels of within-host replication that balance transmission benefits of higher replication with the costs of faster host deaths
32
Q

Tolerance vs. Resistance

A
  • tolerance: the ability of a host to tolerate infection with a pathogen by minimizing the damage done but without impeding replication or transmission of the pathogen
  • resistance: reducing the probability that a host is infected, reduce pathogen replication within the host, and/or increase the speed of pathogen clearance (recovery)
33
Q

Reasons why hosts aren’t more resistant to pathogens?

A
  • trade-offs between resistance traits and other fitness-related traits
  • pathogen evolution to evade/counter host resistance
  • trade-offs among defenses aimed at different parasite types of strains
34
Q

Co-evolutionary dynamics of host-parasite interactions?

A
  • increase of the genetic diversity of both hosts and pathogens via co-speciation events and genetic arms race
35
Q

How are the deaths of individuals in the host population broken down:

A
  1. deaths that are unrelated tot he disease and occurs in unaffected and immune individuals
  2. deaths that occur in infected individuals

BIOL 208 (30 decks)

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