Plasmodium falciparum gametocyte carriage, emergence, clearance and population sex ratios in anaemic and non-anaemic malarious children

Abstract

Anaemia in falciparum malaria is associated with an increased risk of gametocyte carriage, but its effects on transmission have not been extensively evaluated in malarious children. Plasmodium falciparum gametocyte carriage, emergence, clearance, population sex ratios (SR) (defined as the proportion of gametocytes that are male), inbreeding rates and temporal changes in SR were evaluated in 840 malarious children. Gametocyte carriage pre-treatment was at a level of 8.1%. Anaemia at enrolment was an independent risk factor for gametocyte carriage post-treatment. The emergence of gametocytes seven days post-treatment was significantly more frequent in anaemic children (7/106 vs. 10/696, p = 0.002). In the initially detected gametocytes, the proportion of children with a male-biased SR (MBSR) (> 0.5) was significantly higher in anaemic children (6/7 vs. 3/10, p = 0.027). Pre-treatment SR and estimated inbreeding rates (proportion of a mother's daughters fertilised by her sons) were similar in anaemic and non-anaemic children. Pre-treatment SR became more female-biased in non-anaemic children following treatment. However, in anaemic children, SR became male-biased. Anaemia was shown to significantly increase gametocyte emergence and may significantly alter the SR of emerging gametocytes. If MBSR is more infective to mosquitoes at low gametocytaemia, then these findings may have significant implications for malaria control efforts in endemic settings where malaria-associated anaemia is common

Assessing the infectious reservoir of falciparum malaria: past and future

“…In an individual infection, infectiousness per gametocyte may be higher at the beginning of an infection than at the end because of changes in parasite competency (33), sex ratio (34,35) and possibly the development of sexual stage immune responses (36,37,38). Transmission-blocking immunity is boosted by recent exposure to gametocytes (37) and may reduce infectiousness during the course of infections that last several weeks or months.…”

Biology of Plasmodium falciparum gametocyte sex ratio and implications in malaria parasite transmission

“…During malaria infections, P. falciparum the rate of gametocyte production is influenced by several factors, both from the human host [4, 11] (haemoglobin level [12–14], host immunity [15, 16], anti-malarial drug treatment [17–19]) and from the parasite (genetic diversity of infection [20] or mixed infection [21, 22], asexual stage densities [23]). In several cases these studies have not concomitantly investigated whether and how these factors also modified the gametocyte sex ratio, which is defined as the ratio of the number of male gametocytes over female gametocytes and which is typically female biased in Plasmodium parasites [24].…”

Assessment of therapeutic responses to gametocytocidal drugs in Plasmodium falciparum malaria

“…There is variation in reported female to male ratios in acute malaria with values of 3-5 to 1 being observed mainly [ 22 , 24 – 30 ] (Figure 5 ). At lower densities in anaemic children with chronic infections, the female to male gametocyte ratios are reportedly lower [ 31 ], but at the higher densities in acute infections in which drug assessments are performed females consistently comprise >70% of the P. falciparum gametocytes. The biology of male and female gametocytes is very different.…”