Epidemiology (6) (Dan Frank) Flashcards
vehicle transmission of pathogen
single point source like food/cyanide poisoning
DALYs
disability adjusted life year
number of healthy years of life lost due to premature death/disability
combination of morbidity and mortality
Bubonic plague
infects lymphatic system
least serious
painful lymph nodes
30% mortality
Septicaemic plaguq
infects blood
most serious
necrosis - black skin
100% mortality
Pneumonic plague
lungs
chest pain, cough
80% mortality
only one that is transmissible between humans
incidence
number of cases
prevalence
total infected in population
vector-borne protozoan miroparasites
Trypanosoma cruzi - Chagas disease - by kissing bugs, blood transfusion, mother to fetus
Trypanosoma brucei - african sleeping sickness
Plasmodium spp - malaria
Chagas disease:
acute
chronic
pseudocysts form and heart diease
longer, kidney disease and heart disease and necrosis
macroparasites
chronic recurring infections high morbidity low mortality because needs the host usually injest through unsanitised water lay eggs in host that are excreted faecal-oral route
homogeneity
freely mixing population
Ro
basic reproduction number (not rate)
average number of new cases arising form 1 infectious case introduced to population of wholly susceptible individuals
what does the Ro have to be for an epidemic to occur?
> 1
or would only ever be 1 infected because previous would recover and may die out if 1 doesn’t pass it on
Ro equation:
p
c
D
probability that contact results in transmission
frequency of host contacts between infectious and susceptible
average time host is infectious
effective contact rate
S to I
p x c
Re
effective R
when proportion of population is not susceptible
Ro x fraction of susceptibles
reduces with less susceptible individuals so epidemics end if no new susceptibles
how are susceptibles replenished?
birth
migration
mutation of pathogen
incubation period
between infection and onset of disease (symptoms)
latent period
infection to infectiousness
point epidemic
no continual intro of infection - food poisoning
so no curve, it just stops
continuous common source epidemic
more permanent source like cholera - water
propagated progressive source epidemic
spread between hosts
index case
1st individual who brings disease
what is Re for an endemic?
remains 1
CCS
critical community size
min host population needed for pathogen to persist
reservoir host vs carrier
carrier is individual from the reservoir host population
mean burden
no. worms per host
whipworm
inhibits growth and cognitive processes, lower IQ
aims of intervention
control - maintain parasite population at acceptable level
elimination - within population, 0 incidence, local eradication
eradication - zero incidence worldwide
extinction - no longer in nature or lab
herd immunity
right amount of population immune/vaccinated
Ro = 1 + L/A
L = life expectancy A = age when 1st infected
Wakefield
MMR vaccine = autism
caused less vaccines and more measles cases
but paper was false
ring vaccination
not just contacts but everyone within radius
tracing (vaccines)
focus on contact and potential cases
1st and 2nd contacts
anthroponetic
human to anthropod to human
e.g. malaria
vectorial capacity (C)
average no. of potentially infective bites that will be delivered by all vectors feeding on single host in 1 day (units per day)
vectorial capacity (C) equation
V - number of vectors N - number of hosts a^2 - vector biting rate per day h^2 - host choice, proportion of meals on host p - daily vector survival rate n - extrinsic incubation period (EIP)
EIP
latent period of agent inside vector - time after enters vector when can’t transmit yet
how much has the temperature been rising each decade since 1970s?
0.2 degrees
greatest change in the northern hemisphere
ARGO project
measure sea temp changes
what diseases does climate change affect?
why?
mostly vector and water-borne
host env. won’t change with climate but there might be environmental stages of parasite or vector population that will be affected by climate
climate may change values in vectorial capacity equation
dengue
virus
mosquito-borne
tropical
peak in southern oscillation causes peak in epidemics
how did climate change affect BTV?
bluetongue virus
caused to travel geographically - midges are vectors
overwintering - survive over winter or persist in host over winter
MHC
major histocompatibility complex class 1 diversity don't recognise cancer cells as foreign
