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. 2017 Oct 24;10(1):512.
doi: 10.1186/s13071-017-2407-y.

Very high carriage of gametocytes in asymptomatic low-density Plasmodium falciparum and P. vivax infections in western Thailand

Wang Nguitragool  1 , Ivo Mueller  2   3   4 , Chalermpon Kumpitak  5 , Teerawat Saeseu  5 , Sirasate Bantuchai  5 , Ritthideach Yorsaeng  5 , Surapon Yimsamran  6 , Wanchai Maneeboonyang  6 , Patiwat Sa-Angchai  6 , Wutthichai Chaimungkun  6 , Prasert Rukmanee  6 , Supalarp Puangsa-Art  6 , Nipon Thanyavanich  6 , Cristian Koepfli  3   4 , Ingrid Felger  7 , Jetsumon Sattabongkot  5 , Pratap Singhasivanon  8
Affiliations

Very high carriage of gametocytes in asymptomatic low-density Plasmodium falciparum and P. vivax infections in western Thailand

Wang Nguitragool et al. Parasit Vectors. .

Abstract

Background: Low-density asymptomatic infections of Plasmodium spp. are common in low endemicity areas worldwide, but outside Africa, their contribution to malaria transmission is poorly understood. Community-based studies with highly sensitive molecular diagnostics are needed to quantify the asymptomatic reservoir of Plasmodium falciparum and P. vivax infections in Thai communities.

Methods: A cross-sectional survey of 4309 participants was conducted in three endemic areas in Kanchanaburi and Ratchaburi provinces of Thailand in 2012. The presence of P. falciparum and P. vivax parasites was determined using 18S rRNA qPCR. Gametocytes were also detected by pfs25 / pvs25 qRT-PCRs.

Results: A total of 133 individuals were found infected with P. vivax (3.09%), 37 with P. falciparum (0.86%), and 11 with mixed P. vivax/ P. falciparum (0.26%). The clear majority of both P. vivax (91.7%) and P. falciparum (89.8%) infections were not accompanied by any febrile symptoms. Infections with either species were most common in adolescent and adult males. Recent travel to Myanmar was highly associated with P. falciparum (OR = 9.0, P = 0.001) but not P. vivax infections (P = 0.13). A large number of P. vivax (71.5%) and P. falciparum (72.0%) infections were gametocyte positive by pvs25/pfs25 qRT-PCR. Detection of gametocyte-specific pvs25 and pfs25 transcripts was strongly dependent on parasite density. pvs25 transcript numbers, a measure of gametocyte density, were also highly correlated with parasite density (r 2 = 0.82, P < 0.001).

Conclusions: Asymptomatic infections with Plasmodium spp. were common in western Thai communities in 2012. The high prevalence of gametocytes indicates that these infections may contribute substantially to the maintenance of local malaria transmission.

Keywords: Asymptomatic infection; Gametocytes; Malaria; Thailand; Transmission.

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Conflict of interest statement

Ethics approval and consent to participate

All participants gave individual written consent to participate in this study. The study was approved by the Ethics Committee of the Faculty of Tropical Medicine, Mahidol University, Thailand (EC approval number MUTM 2012-044-01).

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

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Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures

Fig. 1
Fig. 1
Parasite prevalence rates (a) and geometric mean parasite densities (b) as a function of age. Whiskers denote 95% confidence intervals
Fig. 2
Fig. 2
Relationships between parasite density and presence of gametocytes. a, b Relationships between parasite density (pv18S or pf18S gene copy number/μl) and gametocyte positivity. c, d Relationship between parasite density and gametocyte density (pvs25 or pfs25 transcripts/μl)
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