Plasmodium falciparum gametocyte dynamics in areas of different malaria endemicity

Abstract

Background: The aim of this study was to identify and compare factors associated with Plasmodium falciparum gametocyte carriage in three regions of differing malaria endemicity.

Methods: Retrospective data from Thailand, The Gambia and Tanzania were used. The data came from large prospective field-based clinical trials, which investigated gametocyte carriage after different anti-malarial drug treatments.

Results: Gametocytaemia was detected during the observation period in 12% of patients (931 out of 7548) in Thailand, 34% (683 out of 2020) in The Gambia, and 31% (430 out of 1400) in Tanzania (p < 0.001). Approximately one third (33%, 680/2044) of the patients with gametocytaemia during the observation period, already had patent gametocytaemia at enrolment (day 0 or day 1): 35% (318/931) in Thailand, 37% (250/683) in The Gambia, 26% (112/430) in Tanzania. Maximum gametocytaemia was usually observed on or before the seventh day after starting treatment (93% in Thailand, 70% in Tanzania and 78% in The Gambia). Lowest gametocyte carriage rates were observed following treatment with artemisinin derivatives, while sulphadoxine-pyrimethamine (SP) was associated with significantly greater development of gametocytaemia than other drug treatments (p < 0.001). The duration of gametocyte carriage was shorter in Thailand by 86% and Tanzania by 65% than in The Gambia. Gametocyte carriage was 27% longer among people presenting with anaemia, and was shorter in duration among patients who received artemisinin derivatives, by 27% in Thailand and by 71% in Tanzania and The Gambia.

Conclusion: This study confirms the independent association of gametocytaemia with anaemia, and the significantly lower prevalence and duration of gametocyte carriage following treatment with an artemisinin derivative. The large differences in gametocyte carriage rates between regions with different levels of malaria transmission suggest that drug interventions to prevent transmission will have different effects in different places.

Figure 1

Relationship between infectivity and gametocytaemia level: (A) Jeffery-Eyles (B) Drakeley et al.

Figure 2

Distribution of admission characteristics of patients in the three countries: (A) parasitaemia, (B) age, (C) haematocrit.

Figure 3

Box plots of admission parasitaemia for patients in the three countries with/without gametocytes present.

Figure 4

Box plots of admission body temperature for patients in the three countries with/without gametocytes present.

Figure 5

Box plots of admission haematocrit for patients in the three countries with/without gametocytes present.

Figure 6

Distribution of AUIC for patients in the three countries. Only patients with gametocytes are presented: in The Gambia 426 out of 779 (53%), in Tanzania 170 out of 347 (50%) and in Thailand 421 out of 4064 (10%). Patients who had any missing gametocytes measurements on day 0, 7, 14, 28 were not included unless the missing values occurred after the day of gametocyte clearance.

Figure 7

Distribution of AUIC for patients in The Gambia for different treatment groups. Only patients with gametocytes are presented: in Artesunate +SP group 197 out of 474 (42%), in SP group 214 out of 289 (74%) and in Chloroquine group 15 out of 36 (42%) patients. Patients who had any missing gametocytes measurements on day 0, 7, 14, 28 were not included unless the missing values occurred after the day of gametocyte clearance.

Figure 8

Distribution of AUIC in patients with gametocytes in Thailand in different treatment groups. Only patients with gametocytes are presented: 253 patients out of 2864 (9%) in the Artemisinin +Other group, 16 out of 298 (5%) in the Halofantrine group and 113 out of 775 (15%) patients in the Mefloquine group. Patients who had any missing gametocytes measurements on day 0, 7, 14, 28 were not included unless the missing values occurred after the day of gametocyte clearance.