Principles of epidemiology Flashcards
Intended Learning Outcomes
-Define key terms in epidemiology
• Explain modes of transmission and the importance of carriers and reservoirs of infection
• discuss a range of public health measures taken to reduce infection
• give examples of (re)emerging diseases
Epidemiology
considers infection at the population level rather than the individual
-how infections spread through populations
Impacts of infectious diseases
- responsible for 16% of human deaths each year
- economic impact on livestock
- threat to rare and endangered species of wildlife
Multi-host pathogens
- able to infect more than one species
- transmission may involve wildlife, livestock and human populations
Emerging infectious diseases
-defined as disease with growing number of cases following its introduction into a host population OR growing number of cases in existing population due to changes in epidemiology
Transmission
- wide range of transmission mechanisms
- linked to pathogen fitness: traits determining transmission are under selection and thus might evolve
Modes of transmission
Vertical: parent to offspring
Horizontal: to any other individual
Modes of transmission
- environmental contamination (macroparasotes, anthrax, cholera)
- vector-borne (malaria, lyme disease, dengue fever)
Aerosol/repiratory (modes transmission)
influenza , measles, TB
H1N1 - easily spread, fatal
H5N1 - slowly spread, often fatal
Close contact/body fluids
-ebola, small pox
STDs - HIV, AIDS , syphillis
Incidence
-no of new caser per unit time
prevalence
-the % of +ve cases
seroprevalence - the % of serum samples reacting positively (containing antibody)
Morbidity
-infections resulting in disease symptoms
Quantifying disease spread:
R0 (basic reproductive number):
-the average no of secondary infections caused by a single infected host in a completely susceptible population
R0=2 or R0>1
the number of infections increases exponentially
-pandemic
R0=1
each infection replaces itself
R0<1
No replacement –> disease goes extinct
Endemic disease
- number of infections remain stable through time
- R0 = 1
Breaking disease transmission chains:
-Isolation, drugs/antibiotics, vaccination, personal protection
Herd immunity
-majority immune , protects others that aren’t immune as it stops spread
R0 of different infectious diseases
- measles R0=10-15
- Polio=5-7
- Ebola=1.5-2.8
- Canine rabies- 1-2
Ability to spread
measured by R0
- speed at which epidemic grows
- proportion that needs to be vaccinated
