Lecture 26. Control of Infections Flashcards
What is the aim of intervention?
Control: Maintains the parasite population to an acceptable level
Elimination: Zero incidence in a defined geographical area (local eradication)
Eradication: Zero incidence worldwide
Extinction: Infectious agent no longer exists in nature or in lab
How can transmissions be prevented?
Mass (random) or targeted vaccination. e.g. smallpox
By risk group e.g. childhood vaccines MMR
Spatial vaccination, e.g ring vaccination - FMD
Reduction in contact by handwashing, condom use, environmental sanitation
How can intervention occur after transmission (to prevent further transmission)?
Infectiousness curtailment - tracing & isolation, or culling
e.g. SARS, hospital MRSA (humans)
FMD, BSE, avian influenza (animals)
In the SIR model, where does vaccination move susceptibles?
Directly into immune class
What is Pc?
The (minimum) proportion of individuals you need to vaccinate
What is the equation for calculating Pc?
Pc = 1 - 1/R0
How is smallpox transmitted?
“Prolonged face-to-face contact” – essentially from nose and mouth droplets, also from sneezing and coughing. Sores and scabs were contagious
What is the R0 of smallpox?
3-6
When was smallpox eradicated?
1980
What does A mean?
Average age of infection (in years)
What does L mean?
Life expectancy (in years)
What does A/L mean?
The proportion of lifetime before infection
The proportion of the population not infected (or previously infected)
What is the equation for R0 involving A and L?
R0 = 1 + L/A
What is ring culling?
Killing every individual within a fixed radius
What does vectorial capacity (C) mean?
The average number of potentially infective bites that will be delivered by all the vectors feeding upon a single host in 1 day
