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The plasticity of Plasmodium falciparum gametocytaemia in relation to age in Burkina Faso.

Ouédraogo AL, Bousema T, de Vlas SJ, Cuzin-Ouattara N, Verhave JP, Drakeley C, Luty AJ, Sauerwein R - Malar. J. (2010)

Bottom Line: Asexual parasite prevalence and gametocyte prevalence decreased with age.This age pattern in gametocytaemia was also evident in the proportion of gametocyte positive slides without concomitant asexual parasites which increased from 13.4% (17/127) in children to 45.6% (52/114) in adults (OR 1.55, 95% CI 1.38-1.74, p < 0.001).The findings of this study suggest that although gametocytes are most commonly detected in children, the proportion of asexual parasites that is committed to develop into gametocytes may increase with age.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre National de Recherche et de Formation sur le Paludisme, Burkina Faso. andrelin.cnrfp@fasonet.bf

ABSTRACT

Background: Malaria transmission depends on the presence of gametocytes in the peripheral blood. In this study, the age-dependency of gametocytaemia was examined by microscopy and molecular tools.

Methods: A total of 5,383 blood samples from individuals of all ages were collected over six cross sectional surveys in Burkina Faso. One cross-sectional study used quantitative nucleic acid sequence based amplification (QT-NASBA) for parasite quantification (n = 412). The proportion of infections with concurrent gametocytaemia and median proportion of gametocytes among all parasites were calculated.

Results: Asexual parasite prevalence and gametocyte prevalence decreased with age. Gametocytes made up 1.8% of the total parasite population detected by microscopy in the youngest age group. This proportion gradually increased to 18.2% in adults (p < 0.001). Similarly, gametocytes made up 0.2% of the total parasite population detected by QT-NASBA in the youngest age group, increasing to 5.7% in adults (p < 0.001). This age pattern in gametocytaemia was also evident in the proportion of gametocyte positive slides without concomitant asexual parasites which increased from 13.4% (17/127) in children to 45.6% (52/114) in adults (OR 1.55, 95% CI 1.38-1.74, p < 0.001).

Conclusions: The findings of this study suggest that although gametocytes are most commonly detected in children, the proportion of asexual parasites that is committed to develop into gametocytes may increase with age. These findings underscore the importance of adults for the human infectious reservoir for malaria.

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The prevalence and density of gametocytes relative to total parasite carriage by microscopy. The number of asexual parasite carriers (with gametocytes) for the different age groups was 0.5-2y: 297 (127); 3-4y: 468 (171); 5-9y: 1053(326); 10-14y: 690(174); 15-19y: 254(72); 20+y: 285(114). Note: data for those carrying gametocytes in the absence of asexual parasitaemia were excluded (see Figure 3).
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Figure 2: The prevalence and density of gametocytes relative to total parasite carriage by microscopy. The number of asexual parasite carriers (with gametocytes) for the different age groups was 0.5-2y: 297 (127); 3-4y: 468 (171); 5-9y: 1053(326); 10-14y: 690(174); 15-19y: 254(72); 20+y: 285(114). Note: data for those carrying gametocytes in the absence of asexual parasitaemia were excluded (see Figure 3).

Mentions: The prevalence of asexual parasites (OR 0.59; 95% CI 0.57-0.62, p < 0.001) and gametocytes (OR 0.70; 95% CI 0.67-0.74, p < 0.001) decreased with age (Figure 1). In parasite positive individuals, the log-transformed density of asexual parasites also decreased over age categories (β = -0.23; 95% CI -0.24 - -0.21, p < 0.001). The gametocyte density in gametocyte carriers also decreased significantly but to a lesser extent (β = -0.041; 95% CI -0.055 - -0.028, p < 0.001). The proportion of infections with concomitant gametocytaemia decreased with age (Figure 2). Whilst 37.0% (110/297) of 0.5-2 year-old carriers of asexual stage parasites concurrently had gametocytes, this was only true for 12.8% (62/485) of the parasite carriers who were 20 years old and above (OR = 0.76;95% CI 0.72-0.81, p < 0.001). In contrast with this trend, the median proportion of gametocytes among all parasites increased with increasing age (Figure 2). Thus, whilst gametocytes only represented 1.8% of the density of the total parasite population in the youngest age group, this proportion gradually increased to a peak of 18.2% in adults (β = 0.42; 95% CI 0.33-0.51, p < 0.001). Although the majority of gametocyte carriers also harboured asexual parasites, microscopical evidence of concurrent asexual parasitaemia was lacking in 17.8% (175/984) of all gametocyte carriers. The proportion of gametocyte carriers without concurrent asexual parasites detected by microscopy was 13.4% (17/127) in children below two years of age and increased with age to 45.6% (52/114) in the oldest age group (Figure 3; trend for age in categories OR 1.55, 95% CI 1.38-1.74, p < 0.001).


The plasticity of Plasmodium falciparum gametocytaemia in relation to age in Burkina Faso.

Ouédraogo AL, Bousema T, de Vlas SJ, Cuzin-Ouattara N, Verhave JP, Drakeley C, Luty AJ, Sauerwein R - Malar. J. (2010)

The prevalence and density of gametocytes relative to total parasite carriage by microscopy. The number of asexual parasite carriers (with gametocytes) for the different age groups was 0.5-2y: 297 (127); 3-4y: 468 (171); 5-9y: 1053(326); 10-14y: 690(174); 15-19y: 254(72); 20+y: 285(114). Note: data for those carrying gametocytes in the absence of asexual parasitaemia were excluded (see Figure 3).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3020678&req=5

Figure 2: The prevalence and density of gametocytes relative to total parasite carriage by microscopy. The number of asexual parasite carriers (with gametocytes) for the different age groups was 0.5-2y: 297 (127); 3-4y: 468 (171); 5-9y: 1053(326); 10-14y: 690(174); 15-19y: 254(72); 20+y: 285(114). Note: data for those carrying gametocytes in the absence of asexual parasitaemia were excluded (see Figure 3).
Mentions: The prevalence of asexual parasites (OR 0.59; 95% CI 0.57-0.62, p < 0.001) and gametocytes (OR 0.70; 95% CI 0.67-0.74, p < 0.001) decreased with age (Figure 1). In parasite positive individuals, the log-transformed density of asexual parasites also decreased over age categories (β = -0.23; 95% CI -0.24 - -0.21, p < 0.001). The gametocyte density in gametocyte carriers also decreased significantly but to a lesser extent (β = -0.041; 95% CI -0.055 - -0.028, p < 0.001). The proportion of infections with concomitant gametocytaemia decreased with age (Figure 2). Whilst 37.0% (110/297) of 0.5-2 year-old carriers of asexual stage parasites concurrently had gametocytes, this was only true for 12.8% (62/485) of the parasite carriers who were 20 years old and above (OR = 0.76;95% CI 0.72-0.81, p < 0.001). In contrast with this trend, the median proportion of gametocytes among all parasites increased with increasing age (Figure 2). Thus, whilst gametocytes only represented 1.8% of the density of the total parasite population in the youngest age group, this proportion gradually increased to a peak of 18.2% in adults (β = 0.42; 95% CI 0.33-0.51, p < 0.001). Although the majority of gametocyte carriers also harboured asexual parasites, microscopical evidence of concurrent asexual parasitaemia was lacking in 17.8% (175/984) of all gametocyte carriers. The proportion of gametocyte carriers without concurrent asexual parasites detected by microscopy was 13.4% (17/127) in children below two years of age and increased with age to 45.6% (52/114) in the oldest age group (Figure 3; trend for age in categories OR 1.55, 95% CI 1.38-1.74, p < 0.001).

Bottom Line: Asexual parasite prevalence and gametocyte prevalence decreased with age.This age pattern in gametocytaemia was also evident in the proportion of gametocyte positive slides without concomitant asexual parasites which increased from 13.4% (17/127) in children to 45.6% (52/114) in adults (OR 1.55, 95% CI 1.38-1.74, p < 0.001).The findings of this study suggest that although gametocytes are most commonly detected in children, the proportion of asexual parasites that is committed to develop into gametocytes may increase with age.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre National de Recherche et de Formation sur le Paludisme, Burkina Faso. andrelin.cnrfp@fasonet.bf

ABSTRACT

Background: Malaria transmission depends on the presence of gametocytes in the peripheral blood. In this study, the age-dependency of gametocytaemia was examined by microscopy and molecular tools.

Methods: A total of 5,383 blood samples from individuals of all ages were collected over six cross sectional surveys in Burkina Faso. One cross-sectional study used quantitative nucleic acid sequence based amplification (QT-NASBA) for parasite quantification (n = 412). The proportion of infections with concurrent gametocytaemia and median proportion of gametocytes among all parasites were calculated.

Results: Asexual parasite prevalence and gametocyte prevalence decreased with age. Gametocytes made up 1.8% of the total parasite population detected by microscopy in the youngest age group. This proportion gradually increased to 18.2% in adults (p < 0.001). Similarly, gametocytes made up 0.2% of the total parasite population detected by QT-NASBA in the youngest age group, increasing to 5.7% in adults (p < 0.001). This age pattern in gametocytaemia was also evident in the proportion of gametocyte positive slides without concomitant asexual parasites which increased from 13.4% (17/127) in children to 45.6% (52/114) in adults (OR 1.55, 95% CI 1.38-1.74, p < 0.001).

Conclusions: The findings of this study suggest that although gametocytes are most commonly detected in children, the proportion of asexual parasites that is committed to develop into gametocytes may increase with age. These findings underscore the importance of adults for the human infectious reservoir for malaria.

Show MeSH
Related in: MedlinePlus