08 dynamics of disease transmission
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DDynamicsynamics
ofof
DDengueengue
TTransmissionransmission
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A Seminar is A Seminar is
a series of meals andsnacks interrupted by
boring lectures
a series of meals andsnacks interrupted by
boring lectures
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Our Learning ObjectivesOur Learning Objectives
Review the dynamics of diseaseReview the dynamics of diseasetransmission.transmission.
Review the various factors whichReview the various factors whichcontribute to disease occurrence.contribute to disease occurrence.
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The Epidemiologic TriangleThe Epidemiologic Triangle
Host
EnvironmentAgent
(Dengue virus)
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Epidemiology entails Epidemiology entails
not just mere presence of factors,not just mere presence of factors,but but
dynamic interactions ofdynamic interactions of
factorsfactors
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Factors Affecting ManFactors Affecting Man
ImmunityImmunityNutritional StatusNutritional Status
Previous DenguePrevious DengueInfectionsInfections
BehaviorBehavior
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Factors in the VirusFactors in the Virus
SerotypeSerotype
Lack Of CrossLack Of Cross--immunityimmunity
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Example of InterplayExample of Interplay
INCREASED
TRANSMISSION
INCREASED
VECTOR
EFFICIENCY
MOSQUITO
DENSITY
TEMPERATURE
HUMIDITY
RAINFALL
HUMIDITY
TEMPERATURE
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More Dynamic InterplayMore Dynamic Interplay
population
Population
density
transportation
Increased
transmissionIncreased contact
rate between man
and mosquito
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Factors Affecting TransmissionFactors Affecting Transmission
Environmental temperatureEnvironmental temperature
HumidityHumidity
Average monthly rainfallAverage monthly rainfall
Mosquito bionomicsMosquito bionomics Mosquito speciesMosquito species
Host immunityHost immunity Population DensityPopulation Density
Access to transportationAccess to transportation
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Mechanics of TransmissionMechanics of Transmission
Transmission isTransmission is
onlyonly through thethrough the
bite of thebite of the
infected femaleinfected femaleAedesAedes mosquitomosquito
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Mechanics of TransmissionMechanics of Transmission
88
--10 days10 days
intrinsicintrinsic
incubationincubation
period in theperiod in the
gut of thegut of the
mosquitomosquito
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Mechanics for TransmissionMechanics for Transmission
Once infected, theOnce infected, themosquito ismosquito is
infected for life.infected for life.
Biting episodes areBiting episodes are
every 3every 3--4 days.4 days.
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Previous TrendsPrevious Trends
Increases every 3Increases every 3--4 years4 years
Dependent on the preDependent on the pre--existing serotypesexisting serotypes
Dictated by a more stable, predictableDictated by a more stable, predictable
meteorological factorsmeteorological factors
Confined to more populated areas.Confined to more populated areas.
2 annual peaks2 annual peaks
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Lately.Lately.
Increasing annual casesIncreasing annual casesYearYear--round transmission with 2round transmission with 2
peakspeaksDecreasing interDecreasing inter--epidemic intervalsepidemic intervals