Normal human serum lysis of non-human trypanosomes and resistance of <i>T. b. rhodesiense</i> and <i>T. b. gambiense</i>

&lt;i&gt;Trypanosoma brucei&lt;/i&gt; can be segregated into three morphologically identical sub-species based on host, geography and pathology. &lt;i&gt;T. b. Brucei&lt;/i&gt; is limited to domestic and wild animals throughout sub-Saharan Africa and is non-infective to humans due to trypanosome lytic factors found in human serum. There are two trypanosome lytic factors in human serum (TLF-1 &#38; 2), both containing the proteins Apolipoprotein L1 (APOL1) and Haptoglobin-related protein (HPR). It has been conclusively demonstrated that the lytic component of TLF is APOL1, although HPR is required for maximal lysis by facilitating uptake of TLF particles via the HpHbR cell surface receptor. &lt;i&gt;T. b. Gambiense&lt;/i&gt; and &lt;i&gt;T. b. Rhodesiense&lt;/i&gt; are able to resist these lytic factors to cause human African sleeping sickness. &lt;i&gt;T. b. Rhodesiense&lt;/i&gt; is able to neutralise APOL1 due to expression of Serum Resistance-Associated gene (SRA). SRA is not found in the more prevalent human infective sub-species, &lt;i&gt;T. b. Gambiense&lt;/i&gt;, which causes over 97 % of reported human cases. Study of &lt;i&gt;T. b. Gambiense&lt;/i&gt; is complicated in that there are two distinct groups. Group 1 is invariably resistant to lysis and by far the more prevalent group. Group 2 &lt;i&gt;T. b. Gambiense&lt;/i&gt; exhibit a variable resistance phenotype and are only found at a small number of Côte d’Ivoire and Burkina Faso foci. Little is known as to how both groups are able to resist lysis by normal human serum; however, members of group 1 &lt;i&gt;T. b. Gambiense&lt;/i&gt; display both reduced expression and activity of HpHbR that may contribute to the resistance phenotype