Gametocyte carriage of Plasmodium falciparum (pfs25) and Plasmodium vivax (pvs25) during mass screening and treatment in West Timor, Indonesia: a longitudinal prospective study

Abstract

Background: A goal of malaria epidemiological interventions is the detection and treatment of parasite reservoirs in endemic areas-an activity that is expected to reduce local transmission. Since the gametocyte is the only transmissible stage from human host to mosquito vector, this study evaluated the pre and post presence of gametocytes during a mass screening and treatment (MST) intervention conducted during 2013 in East Nusa Tenggara, Indonesia.

Methods: RT-qPCR targeting pfs25 and pvs25 transcripts-gametocyte molecular markers for Plasmodium falciparum and Plasmodium vivax, respectively, was performed to detect and quantify gametocytes in blood samples of P. falciparum and P. vivax-infected subjects over the course of the MST study. The presence of both asexual and sexual parasites in microscopic and submicroscopic infections was compared from the start and end of the MST, using proportion tests as well as parametric and non-parametric tests.

Results: Parasite prevalence remained unchanged for P. falciparum (6% = 52/811 versus 7% = 50/740, p = 0.838), and decreased slightly for P. vivax (24% = 192/811 versus 19% = 142/740, p = 0.035) between the MST baseline and endpoint. No significant difference was observed in gametocyte prevalence for either P. falciparum (2% = 19/803 versus 3% = 23/729, p = 0.353, OR = 1.34, 95%CI = 0.69-2.63), or P. vivax (7% = 49/744 versus 5% = 39/704, p = 0.442, OR = 0.83, 95%CI = 0.52-1.31). Even though there was an insignificant difference between the two time points, the majority of parasite positive subjects at the endpoint had been negative at baseline (P. falciparum: 66% = 29/44, P. vivax: 60% = 80/134). This was similarly demonstrated for the transmissible stage-where the majority of gametocyte positive subjects at the endpoint were negative at baseline (P. falciparum: 95% = 20/21, P. vivax: 94% = 30/32). These results were independent of treatment provided during MST activities. No difference was demonstrated in parasite and gametocyte density between both time points either in P. falciparum or P. vivax.

Conclusion: In this study area, similar prevalence rates of P. falciparum and P. vivax parasites and gametocytes before and after MST, although in different individuals, points to a negligible impact on the parasite reservoir. Treatment administration based on parasite positivity as implemented in the MST should be reevaluated for the elimination strategy in the community. Trial registration Clinical trials registration NCT01878357. Registered 14 June 2013, https://www.clinicaltrials.gov/ct2/show/NCT01878357.

Keywords: Gametocyte; Mass screening and treatment; Pfs25; Pvs25.

Conflict of interest statement

The author(s) declare(s) that they have no competing interests.

Figures

Fig. 1

Study framework

Fig. 2

Correlation between gametocyte transcript numbers and parasitaemia density by light microscopy (LM) in P. falciparum (a) and P. vivax (b). In P. falciparum, no correlation was found between gametocyte transcript numbers and parasitaemia density by microscopy (r = 0.198, p = 0.202), whereas in P. vivax, positive correlation was demonstrated (r = 0.514, p < 0.001)

Fig. 3

Correlation between gametocyte transcript numbers and 18S copies by qPCR in P. falciparum (a) and P. vivax (b). A positive correlation was demonstrated between 18S gene copy numbers/µL and gametocyte transcript numbers/µL for aP. falciparum (pfs25) as well as for bP. vivax/pvs25. Linear regression analyses both demonstrated a significance correlation (p < 0.001). Microscopic infections (●) were showing higher transcripts than submicroscopic infections (○)

Fig. 4

Dynamics of parasite and gametocyte in P. falciparum at baseline and endpoint. At baseline, P. falciparum prevalence was 6% (52/811) by microscopy and/or PCR. Half of these 52 subjects were positive by microscopy thus treated (54% = 28/52, ■), and 46% (24/52) were submicroscopic and untreated (□). At the endpoint, only two of each microscopic and submicroscopic group were positive. However, 46 subjects other than the mentioned groups were detected positive by microscopy (n = 32) or PCR (n = 14) ( ). Forty of these 46 subjects had data at baseline: 73% (n = 29) were parasite negative and 27% (n = 11) were infected with other species (P. vivax). Furthermore, similar pattern was observed in gametocyte. At baseline, gametocyte prevalence was 2% (19/803). Seventy-nine percent (15/19) had microscopic parasite and treated ( ), and 21% (4/19) had submicroscopic thus untreated ( ). At the endpoint, only one submicroscopic parasite remained positive. However, 22 subjects other than the mentioned groups were positive for gametocyte ( ). Twenty of these 22 subjects were negative at baseline while two had no data

Fig. 5

Dynamics of parasite and gametocyte in P. vivax at baseline and endpoint. At baseline, P. vivax prevalence was 24% (192/811) by microscopy and/or PCR. A third of these 192 subjects were microscopic positive thus treated (28% = 54/192, ■) and 72% (138/192) were submicroscopic and untreated (□). At the endpoint, six of the microscopic and 43 submicroscopic subjects were positive. In addition, 93 positive subjects (23 by microscopy and 70 by PCR) other than those groups ( ) appeared. Eighty-five of these 93 subjects had data at baseline: 80 were parasite negative and 5 were infected with other species (P. falciparum). A similar pattern was also observed in gametocyte. At baseline, gametocyte prevalence was 7% (49/744). Fifty-three percent (26/49) had microscopic parasite and treated ( ), while 47% (23/49) had submicroscopic and untreated ( ). At the endpoint, only two (one microscopic and one submicroscopic) were positive. However, 37 subjects other than the mentioned groups were positive for gametocyte ( ). Thirty of these 37 subjects were negative at baseline, while seven had no data