Introduction. Globally widespread Plasmodium vivax has long been a burden to the public health. This is particularly due its low density which makes it a difficult target for intervention. Although reported to be less transmissible, these low-level infections may nonetheless be a source of infection. This study aimed to measure the detectability of gametocytes in untreated vivax infections during a series of mass blood surveys.
Material and methods. Finger-pricked blood samples were collected from 685 individuals during two mass blood surveys (MBS) conducted in Malaka District, East Nusa Tenggara in June and September 2013. Light microscopy and Real-Time PCR targeting 18S rRNA were deployed to determine parasitemia status at both time points. Gametocytes were detected using RT-qPCR targeting pvs25 transcript in the subset of positive samples.
Results. Prevalence of Plasmodium vivax parasite decreased slightly, from 24% (164/685) at baseline to 20% (134/685) at endpoint (p=0.057). Meanwhile, gametocyte prevalence was relatively similar between both time points (7%=42/600 versus 5%=32/600, p=0.280). At baseline, 74% (122/164) of infections were subpatent thus untreated. Nevertheless, 59% (72/122) of these infections became negative at endpoint, whereas 60% (80/134) of positive individuals at endpoint had been negative at baseline. Similarly, 95% (19/20) of gametocyte positive at baseline were negative at endpoint despite no treatment being given, while 94% (30/32) of gametocyte positives at endpoint had been previously negative.
Conclusion. MBS did not impact the frequency of gametocytemia of P. vivax. New carriers dominated following MBS. Some strategy other than MBS may be required for detection and removal of these infectious reservoirs.