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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