Spleen enlargement and genetic diversity of Plasmodium falciparum infection in two ethnic groups with different malaria susceptibility in Mali, West Africa

Abstract

The high resistance to malaria in the nomadic Fulani population needs further understanding. The ability to cope with multiclonal Plasmodium falciparum infections was assessed in a cross-sectional survey in the Fulani and the Dogon, their sympatric ethnic group in Mali. The Fulani had lower parasite prevalence and densities and more prominent spleen enlargement. Spleen rates in children aged 2-9 years were 75% in the Fulani and 44% in the Dogon (P<0.001). There was no difference in number of P. falciparum genotypes, defined by merozoite surface protein 2 polymorphism, with mean values of 2.25 and 2.11 (P=0.503) in the Dogon and Fulani, respectively. Spleen rate increased with parasite prevalence, density and number of co-infecting clones in asymptomatic Dogon. Moreover, splenomegaly was increased in individuals with clinical malaria in the Dogon, odds ratio 3.67 (95% CI 1.65-8.15, P=0.003), but not found in the Fulani, 1.36 (95% CI 0.53-3.48, P=0.633). The more susceptible Dogon population thus appear to respond with pronounced spleen enlargement to asymptomatic multiclonal infections and acute disease whereas the Fulani have generally enlarged spleens already functional for protection. The results emphasize the importance of spleen function in protective immunity to the polymorphic malaria parasite.

Ethnic differences in susceptibility to malaria: What have we learned from immuno-epidemiological studies in West Africa?

“…The higher incidence of spleen enlargement in the Fulani might reflect a hyper immune reactivity of this secondary lymphoid organ (Bereczky et al, 2006;Vafa et al, 2009a;Alkadarou et al, 2013), a hypothesis supported by several studies which consistently show that the Fulani mount a more robust humoral immune response, as reflected by increased titers of anti-plasmodial antibodies (Modiano et al, 1998(Modiano et al, , 1999Bolad et al, 2005;Farouk et al, 2005a;Vafa et al, 2009a). The levels of malaria blood-stage antibodies anti-AMA1 and anti-MSP1 were significantly increased in Fulani, suggesting the higher specific humoral responses against AMA1 and MSP1 in this ethnic group (Dolo et al, 2012a).…”

“…Several studies have demonstrated that the Fulani are less parasitized, have a higher incidence of spleen enlargement (Bereczky et al, 2006) and are less affected by malaria sickness, despite the fact that people in these areas are exposed to malaria at the same level. Moreover, it has been observed that the pyrogenic threshold of parasitemia was 1,000 parasites/l of blood in the Dogon and 5,000 parasites/l of blood in the Fulani (Dolo et al, 2012b) and that the Fulani present more often with symptoms of anemia than the Dogon, despite their lower susceptibility to malaria (Dolo et al, 2012c).…”

Cytokine responses of CD4+ T cells during a Plasmodium chabaudi chabaudi (ER) blood-stage infection in mice initiated by the natural route of infection

“…Splenomegaly is a characteristic of malaria infections, observed in human infections and rodent models [17-19]. In mice, this is thought to be due in part to the haematopoetic response to the high numbers of RBC lost through infection, and to the trapping of leukocytes in the spleen [20-23].…”

Splénomégalie palustre hyper-réactive

“…Si la SPH est avant tout secondaire à une infection à P. falciparum, elle ne semble pas liée à des souches plasmodiales particulières au sein de cette espèce [8].…”