Publication: Plasmodium vivax genetic diversity and heterozygosity in blood samples and resulting oocysts at the Thai–Myanmar border
Issued Date
2017
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eng
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Mahidol University
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BioMed Central
Bibliographic Citation
Malaria Journal. vol.16, No. 1 (2017), 355
Suggested Citation
Ingfar Soontarawirat, Andolina, Chiara, Paul, Richard, Day, Nicholas P. J., Nosten, Francois, Woodrow, Charles J., Mallika Imwong Plasmodium vivax genetic diversity and heterozygosity in blood samples and resulting oocysts at the Thai–Myanmar border. Malaria Journal. vol.16, No. 1 (2017), 355. doi:10.1186/s12936-017-2002-x Retrieved from: https://repository.li.mahidol.ac.th/handle/20.500.14594/43779
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Title
Plasmodium vivax genetic diversity and heterozygosity in blood samples and resulting oocysts at the Thai–Myanmar border
Other Contributor(s)
Mahidol University. Faculty of Tropical Medicine. Department of Clinical Tropical Medicine
Mahidol University. Faculty of Tropical Medicine. Shoklo Malaria Research Unit
Mahidol University. Faculty of Tropical Medicine. Mahidol Oxford Research Unit
Mahidol University. Faculty of Tropical Medicine. Department of Molecular Tropical Medicine and Genetics
Mahidol University. Faculty of Tropical Medicine. Shoklo Malaria Research Unit
Mahidol University. Faculty of Tropical Medicine. Mahidol Oxford Research Unit
Mahidol University. Faculty of Tropical Medicine. Department of Molecular Tropical Medicine and Genetics
Abstract
Background: Polyclonal blood-stage infections of Plasmodium vivax are frequent even in low transmission settings,
allowing meiotic recombination between heterologous parasites. Empirical data on meiotic products are however
lacking. This study examined microsatellites in oocysts derived by membrane feeding of mosquitoes from bloodstage P. vivax infections at the Thai–Myanmar border.
Methods: Blood samples from patients presenting with vivax malaria were fed to Anopheles cracens by membrane
feeding and individual oocysts from midguts were obtained by dissection after 7 days. DNA was extracted from
oocysts and parental blood samples and tested by microsatellite analysis.
Results: A focused study of eight microsatellite markers was undertaken for nine blood stage infections from 2013,
for which derived oocysts were studied in six cases. One or more alleles were successfully amplifed for 131 oocysts,
revealing high levels of allelic diversity in both blood and oocyst stages. Based on standard criteria for defning minor
alleles, there was evidence of clear deviation from random mating (inbreeding) with relatively few heterozygous
oocysts compared to variance across the entire oocyst population (FIT = 0.89). The main explanation appeared to
be natural compartmentalisation at mosquito (FSC = 0.27) and human stages (FCT = 0.68). One single human case
produced a total of 431 successfully amplifed loci (across 70 oocysts) that were homozygous and identical to parental
alleles at all markers, indicating clonal infection and transmission. Heterozygous oocyst alleles were found at 15/176
(8.5%) successfully amplifed loci in the other fve cases. There was apparently reduced oocyst heterozygosity in
individual oocysts compared to diversity within individual mosquitoes (FIS = 0.55), but this may simply refect the diffculty of detecting minor alleles in oocysts, given the high rate of amplifcation failure. Inclusion of minor allele peaks
(irrespective of height) when matching peaks were found in related blood or oocyst samples, added 11 minor alleles
for 9 oocysts, increasing the number of heterozygous loci to 26/176 (14.8%; p = 0.096).
Conclusion: There was an apparently low level of heterozygous oocysts but this can be explained by a combination
of factors: relatively low complexity of parental infection, natural compartmentalisation in humans and mosquitoes,
and the methodological challenge of detecting minor alleles.