Association of TNF (rs1800629) promoter polymorphism and schistosomiasis with sub-microscopic asymptomatic Plasmodium falciparum infections in a schistosomiasis-endemic area in Zimbabwe.

Abstract

Infection with Plasmodiumfalciparum parasites may result in a wide spectrum of symptoms ranging from asymptomatic to mild or severe. A number of factors are associated with this heterogeneous response to P.falciparum infection. In the present study, associations of sub-microscopic asymptomatic P.falciparum with Schistosoma species and TNF (rs1800629) polymorphism were investigated. 361 clinically healthy primary school children were microscopically screened for S.haematobium, S.mansoni and P.falciparum. Sub-microscopic asymptomatic P.falciparum infections were determined by PCR. Genotypic profiles were identified using ARMS-PCR. Logistic regression was used to assess the association of sub-microscopic asymptomatic P.falciparum with Schistosoma species and TNF (rs1800629) polymorphism. 17.2% of the children were infected with S.mansoni, and 27.4% were infected with S.haematobium. Microscopic examination of thick smears detected only one child infected with P.falciparum. Based on PCR results, 46.1% were infected with sub-microscopic asymptomatic P.falciparum. Children carrying heterozygous AG (OR: 16.964, 95% CI: 0.496-586.547) and homozygous GG (OR: 2.280, 95% CI: 0.111-46.796) genotypes of rs1800629 were associated with an increased likelihood of sub-microscopic asymptomatic P.falciparum infections compared with those carrying homozygous AA genotype. Children without S. haematobium infections (OR: 1.051, 95% CI: 0.146-8.985) and S. mansoni (OR: 2.658, 95% CI: 0.498-14.184) also had an increased likelihood (risk) of being infected with sub-microscopic asymptomatic P.falciparum compared with the Schistosoma-infected groups. However, all the associations observed were not statistical significant. No associations were observed between rs1800629 and schistosomiasis with sub-microscopic asymptomatic P.falciparum infections. This study also reports a high prevalence of sub-microscopic asymptomatic P.falciparum infection concomitant with low malaria transmission.