Biology Reference
In-Depth Information
CHAPTER TWO
Relapse
Nicholas J. White
*
,
1
, Mallika Imwong
†
*Mahidol Oxford Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
†
Department of Molecular Tropical Medicine and Genetics, Faculty of Tropical Medicine,
Mahidol University, Bangkok, Thailand
1
Corresponding author: nickw@tropmedres.ac
Contents
1. Introduction
114
2. History
115
2.1. EuropeanandNorthAmericanVivaxMalaria
115
2.2. DiscoveryoftheLiverStages
119
3. PhenotypicVariationin
P. vivax
119
4. RelapseDeterminants
120
4.1. EfectsoftheSporozoiteInoculumonRelapseIntervals
120
4.2. ArtiicialversusNaturalInfections
123
4.3. EfectsofDrugsonRelapseIntervals
124
4.4. TheProportionof
P. vivax
InfectionswhichRelapse
124
5. GeographicDistributionofRelapsePhenotypes
125
6. TheEfectsofAgeandImmunityonRelapse
129
7. DrugEfectsonRelapse
129
8. VivaxMalariaFollowingFalciparumMalaria
131
9. ThePeriodicityofRelapse
131
9.1. TheoriestoExplainthePeriodicityofRelapse
133
9.2. RelapsesofVivaxMalariaArisefromActivationofLatentHypnozoites(ALH)
134
9.3. TheStimulusforHypnozoiteActivation
137
10. ImplicationsforEpidemiologicalAssessment
142
10.1. PracticalImplications
143
Acknowledgements
144
Abstract
Plasmodium vivax
isamajorcauseoffebrileillnessinendemicareasofAsia,Centraland
SouthAmerica,andthehornofAfrica.
P. vivax
infectionsarecharacterizedbyrelapsesof
malariaarisingfrompersistentliverstagesoftheparasite(hypnozoites),whichcanbe
preventedcurrentlyonlyby8-aminoquinolineanti-malarials.Tropical
P. vivax
infections
relapseatapproximately3-weekintervalsifrapidlyeliminatedanti-malarialsaregiven
fortreatment,whereasintemperateregionsandpartsofthesub-tropics,
P. vivax
infec-
tionsarecharacterizedbyeithera long incubationora long-latencyperiodbetween
illnessandrelapse- inbothcasesapproximating8-10 months.Theepidemiologyof
the different relapse phenotypes has not been defined adequately despite obvious
