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

OBJECTIVES Infection with P. falciparum 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 between sub-microscopic asymptomatic P. falciparum with Schistosoma species and TNF (rs1800629) polymorphism were investigated. METHODS 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. Logistics regression was used to assess the association between sub-microscopic asymptomatic P. falciparum with Schistosoma species and TNF (rs1800629) polymorphism. RESULTS 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 to 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 to the Schistosoma-infected groups. However all the associations observed were not statistical significant. CONCLUSION 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.