Transmissibility and virulence of drug sensitive and resistant Trypanosoma brucei rhodesiense isolates from Kenya

Abstract

Trypanosome parasite isolates are routinely collected within Human African Trypanosomiasis foci in the region and cryopreserved in a parasite cryobank at the Trypanosomiasis Research Center of the Kenya Agriculture Research Institute (KARI-TRC). Investigations were conducted to compare pathogenicity and transmissibility of drug sensitive (KETRI 2427) and resistant (EATRO 237) Trypanosoma brucei rhodesiense isolates obtained from the KARI-TRC bank. Glossina pallidipes (tsetse fly vector) was used for transmission in the mouse model. To determine transmission rates, two groups of tsetse flies (150 flies each) were separately infected with the drug sensitive and resistant T. b. rhodesiense isolates and were allowed to feed separately on Swiss white mice (one fly per mouse) in a controlled laboratory setting. The infected mice were regularly monitored for 1) pre-patent period (PPP), 2) parasitaemia level, 3) body weight, 4) packed cell volume (PCV) and 5) survival time for a period of 60 days-post-infection (dpi). The infection rates were significantly higher (p<0.05) in drug sensitive (67%) than in the resistant isolate (29%). The values obtained for survival were significantly lower in mice infected by either isolates than the controls. However, mice infected with sensitive isolate had significantly reduced survivorship (days) than those infected with the resistant isolates (days). Infections by either isolates did not significantly affect body weights of the experimental mice. Pre-patent periods among the isolates in mice were also similar. The observed significant differences in parasitaemia, survival time and PCV between the isolates in mice suggests differences in transmissibility and virulence between the isolates, which may be influenced by drug resistance gene in the parasite. Drug resistance appears to putatively reduce virulence and transmissibility of the parasite. This phenomenon can present major challenges in the management in the field.