Characterization of an Anomalous Trypanosoma Brucei Rhodesiense Isolate from Busia County, a Sleeping Sickness Focus in Western Kenya

Abstract

This study was carried out to characterize an anomalous Trypanosoma brucei rhodesiense isolate (KETRI 3971) that was obtained from Obekai village; Busia County, Kenya and compared with three non-anomalous isolates (KETRI 2482, KETRI 2382 and KETRI 3799) that were obtained from the neighboring locality. All isolates were obtained from patients and later preserved at the parasite cryo-bank in KALRO- BioRI (Muguga). DNA was amplified to target the ITS (internally transcribed spacer) region and SRA genes. The virulence of the isolates was compared following in vivo infection of Swiss white mice(n=10) per isolate, which were regularly checked for pre-patent period (PPP), extent of parasitaemia, packed cell volume (PCV) and survival time for 30 days-post-infection (dpi) duration. The susceptibility of the isolates to Suramin was also compared following in vivo infection in Swiss white mice (n=5) per isolate. In addition, Glossina pallidipes(n=100) and G morsitans(n=100) per isolate were used to determine the infection and transmission ratesusing a mouse model. All the four isolates were successfully amplified using the trypanosome specific ITS marker confirming that these isolates were trypanosomes. Amplification of all the four isolates using serum resistance antigen (SRA) gene primers yielded specific PCR products, thus confirming the isolates asT. b. rhodesiense. All infected mice had pre-patent parasitaemia duration of 3-6 days. Mice infected with the anomalous isolate had low parasitaemia profile, unaffected PCV and they all survived to the end of the experiment compared to mice infected with the non-anomalous isolates whose parasitaemia levels were typically high with a significant decline xiv (p<0.01) in PCV and a reduced survivorship (days) and high mortality. The observed low parasitaemia profile together with high PCV, low mortality in mice infected with the anomalous KETRI 3971 isolate is suggestive of a variant form of Trypanosome brucei rhodesiense that is possibly less virulent and causing a chronic form of infection in humans. All trypanosome isolates under study were susceptible to Suramin with no relapse detected following treatment of infected mice. Glossina pallidipes were the more susceptible species to infection and were more efficient in transmitting infective trypanosomes compared to G morsitans. This study reveals and reports for the first time, the existence of a T. brucei rhodesiense strain in Busia County that causes a chronic form of infection typically not associated with the T. b. rhodesiense infection. It also reveals that G. pallidipes was the suitable vector that competently pick, establish and transmit the anomalous KETRI 3971 isolate. In light of these findings, effective intervention measures will be necessary to control the possible transmission of the parasite strain through rapid diagnosis and treatment of infected persons as well as controlling the spread of the susceptible Glossina vector