BIOL 437 Week Five Part 2 Flashcards
stable endemicity
- relatively stable incidence of infection or disease
eg. HIV
seasonal endemicity
- some waterborne and respiratory infections
eg. cholera, seasonal influenza
immunizing infections
- recurrent outbreaks with predictable inter epidemic periods
ex. measles, whooping cough
pathogen characteristics that result in population cycles
- high transmissibility
- short infectious period
- transmission-blocking immunity upon recovering
epidemic will not occur until
-enough new susceptible individuals are born
inter-epidemic period determined by
-birth rate of host
-transmission rate of pathogen
*vaccination reduces number of sustceptible individuals born into a population
>mass vaccination will increase the inter-epidemic period
seasonality
- Environmentally-forced disease dynamics
- Term-time forcing
- Behaviourally associated
environmentally forced disease
-winter peak in influenza
>time of year depnds on hemisphere
-vector borne infections
-water-borne infections
term-time forcing
- seasonal changes in contacts amon hosts
- increase contact between school age children
ex. whooping cough
behaviourally associated
-urban-rural seasonal migration
>low contact during wet season: rural
>higher contact rate during dry season: work in urban settings
ex. measles
host diversity
-ex. chicken pox
-persistant mechanism within individual host
>dormant in NS, re-emerges when host is an adult as shingles
>respiratory transmission and direct contact with rash
host range
- ex. rabies vaccine
- wide
- high affinity for nervous tissue
for infection to spread
-average number of new infetions is greater than or equal to old infections
for infection to persist
-necessary for at least one infected individual to pass that onward
larger populations
-have more opportunity for transmission
critical community size
- population size where transmission of a specific pathogen is a certainty
- smallest population size for which a given population does NOT go extinct
vaccination and effective community size
-vaccination reduces it
>reduces number of susceptibles
probability of extinction before a major epidemic
-equal to rate of recovery divided by transmission rate
pathogen microbe interactions
-ex. Bordetella: whooping and kennel cough
-whooping cough is only humans
>absence of Type VI secretion system
social network
- network of people connected by potential disease transmission events
- create maps
- important for contact tracing
- road maps for spread of infectious disease
nodes
-hosts
edges between nodes
-potential disease transmission events
degree distribution
- of a node is the number of edges it has
- number of contacts the person has
- affects R.
variance in degree distribution
-greatly affected by R.
>some will have more or less contacts than average
-higher R. in high variance network
