GENETIC DIVERSITY OF T. B. RHODESIENSE SERUM RESISTANCE ASSOCIATED GENE IN MALAWIAN ISOLATES

Abstract

BackgroundHuman African Trypanosomiasis (HAT) is a health burden in most remote areas of Sub-Saharan Africa. Only 2 species of the Trypanosome parasites, namely, T. b. rhodesiense and T. b. gambiense can establish infection in humans whereas other trypanosome parasites are lysed by human serum APOL-1 protein. The mechanism of T. b. gambiense resistance to APOL-1 activity is complex and involves several parasite factors. On the other hand, T. b. rhodesiense evades the lytic activity of APOL-1 by intracellular expression of a Serum Resistance Associated (SRA) gene that binds to APOL-1 when uptaken by the parasite thereby disabling APOL-1 from causing cellular membrane rupture. APOL-1 has 2 variants, namely, APOL-1 G1 and APOL-1 G2 with the later having mutations on the SRA binding sites which restores APOL-1 lytic activity in parasite lysis assays. This phenomenon remains elusive in clinical setting as limited data is available. In the present study we investigated the genetic diversity of T. b. rhodesiense SRA gene and APOL-1 genotypes in Malawian r-HAT clinical phenotypes. MethodsT. b. rhodesiense SRA gene from Malawi endemic HAT samples (n= 77) as well as from Zambia and Uganda (n= 13) was amplified by PCR and PCR products were commercially sequenced. APOL-1 variants were identified by restriction fragment length polymorphism (RFLP) after a PCR amplification (n= 61). Results and conclusionSequencing data revealed a heterozygosity of the SRA gene within Malawi T. b. rhodesiense isolates. Malawian SRA gene was genetically different from some isolates in Uganda and Zambia. Contrary to the current understanding that APOL-1 G2 variants are immune to T. b. rhodesiense infection, severe cases of r-HAT in G2 individuals were identified. This study has brought new insight in understanding the determinants of r-HAT severity.