Evolution of Infectious Diseases Flashcards
What are the levels or stages of an infectious disease?
- Level 1: Exposure
- Level 2: Infection
- Level 3: Transmission
- Level 4: Epidemic spread
What are the top three reservoirs of emerging infectious diseases?
- Ungulates
- Carnivores
- Rodents
How does evolutionary relatedness influence likelihood of sharing pathogens?
Closely related species tend to share a lot of similar pathogens compared to those more distantly related
What is the primary transmission mode of emerging infectious diseases?
Vector-borne
What taxonomic groups of are most likely to be an emergent infectious disease?
- Viruses followed by protozoa
- Particularly RNA viruses (maybe due to high mutation rate)
What are the key parameters in the theory of emerging infectious disease? (3)
- Transmissibility of pathogen from one host to another
- Average number of contacts
- Coefficient of variation in number of contacts
What does the mean number of contacts, variation in the number of contacts and transmissibility influence probability of establishment of a new disease?
- Increased transmissibility = increased likelihood of establishment
- Increased number of contacts = increased likelihood of establishment
- Greater heterogeneity in contacts = increased likelihood of establishment
How does mutation rate influence emergence of novel disease?
For those pathogens that begin as poorly adapted to their environment, increased mutation rate has large increase in emergence
Relationship is reversed for pathogens that are already well-adapted and can sustain themselves in the population, but relationship isn’t as dramatic
How does selection typically act on transmission rate?
Selection is always pushing the transmission rate upwards
How does selection typically act on virulence?
Selection is always pushing virulence downwards
How does the number of susceptible hosts influence the strength of selection on transmission?
The strength of selection on transmission is proportional to the density of susceptible hosts in the population
How are transmission rates related to one another early and late during the infection of an individual?
Genotypes that are highly transmissible in the early stages of infection have low levels of transmission late in the infection, and vice versa
How does selection on transmission/virulence change from epidemic to endemic phases of disease spread?
- Epidemic: selects for high levels of transmissibility early on, which is then selected against later on
- Endemic: selection for low transmissibility in early stages, followed by selection for high transmissibility in later stages
How do lockdowns influence the rate of evolution and the strength of selection on transmission?
- Rate of evolution slows down during periods of lockdown
- Same with strength of selection
How does adaptation influence spread of disease?
Adaptations that increase transmissibility increase disease spread
