Host haematological factors influencing the transmission of Plasmodium falciparum gametocytes to Anopheles gambiae s.s. mosquitoes

Abstract

SummaryWe investigated the relationship between selected host haematological and parasitological parameters and the density and infectivity of Plasmodium falciparum gametocytes. 143 individuals (age range 1-62 years) attending an outpatient clinic in Farafenni, The Gambia, who had peripheral blood gametocytaemia were recruited (mean gametocyte density 123.7/l, range 5-17,000/l). Of the parameters measured, packed cell volume (PCV), reticulocyte count (RetC) and lymphocyte count (LyC) were significantly associated with gametocyte density (r ϭ Ϫ 0.17, P Ͻ 0.05; r ϭ 0.21, P Ͻ 0.01; r ϭ 0.18, P Ͻ 0.05, respectively). Data from membrane feeding experiments in which 15 or more mosquitoes were dissected showed that 60.7% (53/87) of gametocyte carriers infected one or more mosquitoes. Gametocyte density was strongly correlated with transmission success (TS) (r ϭ 0.3, P Ͻ 0.005) and, in successful infections, with both mosquito prevalence (MP) (r ϭ 0.36, P Ͻ 0.005) and mean oocyst burden (MOB) (r ϭ 0.65, P Ͻ 0.0001). None of the other factors measured were significantly associated with any of these indices in bivariate analysis. Regression modelling showed that both gametocyte density and PCV were positively associated with gametocyte carrier infectivity to mosquitoes (LR 2 ϭ 100.7 and 47.2, respectively) and, in successful infections, with MOB (␤ ϭ 0.16, t ϭ 4.9, P Ͻ 0.001; ␤ ϭ 0.02, t ϭ 2.3, P Ͻ 0.05, respectively). The positive association with PCV suggests that blood meal quality influences infection probably as a nutritional requirement, however, as this effect was most apparent at high gametocyte densities, its epidemiological significance is questionable. Though the haematological parameters associated with gametocyte density are a direct consequence of asexual infection, they may also represent an adaptive mechanism for optimization of sexual stage development.

Gametocitemia de Plasmodium falciparum según la respuesta terapéutica a sulfadoxina-pirimetamina y cloroquina en dos municipios de Antioquia, Colombia.

“…El efecto de la CQ y la SP sobre la gametocitemia no está bien establecido. Los estudios realizados al respecto muestran resultados diferentes y, por tanto, cualquier conclusión debe hacerse con cautela (7,(13)(14)(15)(16)(17)19,20). En nuestro estudio encontramos que los pacientes que fueron tratados con SP presentaron gametocitemia durante todo el seguimiento (en especial entre los días 3 y 14) más altas que los pacientes tratados con SP+CQ, pero las diferencias no fueron estadísticamente significativas; esto concuerda con lo encontrado en algunos estudios (15,17).…”

“…Diversos estudios han informado que el número de gametocitos circulantes en P. falciparum está influenciado tanto por aspectos del hospedero (la respuesta inmune), del parásito (la cantidad de parásitos asexuales y su capacidad para diferenciarse a gametocitos), como por aspectos externos (el tipo de medicamento suministrado en el control de los estadios asexuales) (1,3,(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21). Además, algunos estudios muestran que los pacientes con falla al tratamiento antimalárico o aquéllos que requieren más tiempo para eliminar los parásitos asexuales, presentan mayor número de gametocitos circulantes que los pacientes que responden adecuadamente al tratamiento o cuya parasitemia asexual desaparece más rápidamente con el tratamiento suministrado (11,17,18).…”

Gametocytemia in Plasmodium Vivax and Plasmodium Falciparum Infections

“…Recent work has focused on children in sub-Saharan Africa infected with P. falciparum in whom gametocytemia is associated with an absence of fever (von Seidlein et al, 2001;Sowunmi et al, 2004), low (von Seidlein et al, 2001;Sowunmi et al, 2004) or high (Githeko et al, 1992;Drakeley et al, 1999;Bousema et al, 2004) asexual parasitemia, and either anemia (Drakeley et al, 1999;von Seidlein et al, 2001) or its absence (Sowunmi et al, 2004).…”

Plasmodium vivax Blood-Stage Dynamics

“…Recent studies indicate that Duffy-antigen expression is higher on reticulocytes (Woolley et al, 2000), that gametocyte production and infectivity in P. falciparum are higher in reticulocytotic blood, e.g., from sickle-cell anemics (Trager and Gill, 1992;Drakeley et al, 1999;Trager et al, 1999), that P. falciparum infectivity increases with the proportion of male gametocytes (Robert, Read et al, 1996), and that stimulation of erythropoesis, but not reticulocytosis per se, shifts gametocyte sex ratios in P. gallinaceum and P. vinckei toward males (Paul et al, 2000). This new conjunction suggests possible links to the homeostatic mechanisms that boost reticulocyte production in response to red blood cell depletion and potential insights into the within-and between-host dynamics of mixed-species Plasmodium infections (Snewin et al, 1991; Bossert, 1997, 1999;Worku et al, 1997;Mason and McKenzie, 1999).…”