Relapses of Plasmodium vivax infection usually result from activation of heterologous hypnozoites.
BACKGROUND
Relapses originating from hypnozoites are characteristic of Plasmodium vivax infections. Thus, reappearance of parasitemia after treatment can result from relapse, recrudescence, or reinfection. It has been assumed that parasites causing relapse would be a subset of the parasites that caused the primary infection.


METHODS
Paired samples were collected before initiation of antimalarial treatment and at recurrence of parasitemia from 149 patients with vivax malaria in Thailand (n=36), where reinfection could be excluded, and during field studies in Myanmar (n=75) and India (n=38).


RESULTS
Combined genetic data from 2 genotyping approaches showed that novel P. vivax populations were present in the majority of patients with recurrent infection (107 [72%] of 149 patients overall [78% of patients in Thailand, 75% of patients in Myanmar {Burma}, and 63% of patients in India]). In 61% of the Thai and Burmese patients and in 55% of the Indian patients, the recurrent infections contained none of the parasite genotypes that caused the acute infection.


CONCLUSIONS
The P. vivax populations emerging from hypnozoites commonly differ from the populations that caused the acute episode. Activation of heterologous hypnozoite populations is the most common cause of first relapse in patients with vivax malaria.
Imwong
Mallika
M
Department of Clinical Tropical Medicine, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
Snounou
Georges
G
Pukrittayakamee
Sasithon
S
Tanomsing
Naowarat
N
Kim
Jung Ryong
JR
Nandy
Amitab
A
Guthmann
Jean-Paul
JP
Nosten
Francois
F
Carlton
Jane
J
Looareesuwan
Sornchai
S
Nair
Shalini
S
Sudimack
Daniel
D
Day
Nicholas P J
NP
Anderson
Timothy J C
TJ
White
Nicholas J
NJ
D000293:Adolescent; D000328:Adult; D000818:Animals; D000962:Antimalarials / Q000008:administration & dosage / Q000627:therapeutic use*; D002648:Child; D002738:Chloroquine / Q000008:administration & dosage / Q000627:therapeutic use; D017931:DNA Primers; D006801:Humans; D007194:India / Q000453:epidemiology; D016780:Malaria, Vivax / Q000097:blood / Q000188:drug therapy* / Q000453:epidemiology / Q000469:parasitology*; D002052:Myanmar / Q000453:epidemiology; D010966:Plasmodium vivax / Q000235:genetics* / Q000472:pathogenicity; D012150:Polymorphism, Restriction Fragment Length; D011319:Primaquine / Q000008:administration & dosage / Q000627:therapeutic use; D015800:Protozoan Proteins / Q000235:genetics; D012008:Recurrence; D013785:Thailand / Q000453:epidemiology; D016896:Treatment Outcome
D000962:Antimalarials; D017931:DNA Primers; D015800:Protozoan Proteins; D002738:Chloroquine; D011319:Primaquine