Direct transmission—pathogen goes from human to human (ex. influenza, measles)
Zoonotic diseases—transmit from animal populations to human populations
Vector borne disease—pathogen transmits from the host to the human
There are also environmental factors that allow for the spread of these diseases etc.
These terms are fluid!
Epidemic- rapid spread of disease to a large number of people in a short period of time
Why do epidemics peak and then decrease?
Epidemics have to come back down due to depletion of susceptible individuals—if you’ve been
infected you’re no longer susceptible.
We have recurring epidemics because susceptibles become depleted
- immunity fades
- susceptibles are replenished—babies without immunity are born
Emerging infectious diseases—why do they emerge in human populations? Eg. Zika, Ebola,
MERS, H1N1, SARS
Emergence may be related to changes in the environment, pathogen population,
reservoir/vector population, or host population.
- Urbanization changes the landscape and the way vectors, humans, pathogens interact
with each other.
Disease ecology is different from epidemiology…. kind of.
Epidemiology: is there a link between Zika virus and microcephaly?
Disease ecology: What factors are driving the spatial clustering of microcephaly in Brazil?
We make mathematical models for the amount of infectious diseases.
The most basic framework: Susceptible Infectious recovered
R0 = number of secondary cases caused by each primary case in a fully susceptible population
R0 > 1 – the disease is growing, so it is called an epidemic
R0 < 1—disease cases can’t replace themselves and the disease will die out
R0 = 1—dise