Transmissibility and virulence study of drug sensitive and resistant Trypanosoma congolense in Mice

Abstract

To enhance our understanding of epidemiology of Trypanosoma congolense infection and to mitigate the development of drug resistance in the field, this study sought to assess whether there is any correlation between sensitivity and/or resistance to drug and virulence, and also to establish the relative efficiency of transmission of drug sensitive and resistant T. congolense by Glossina pallidipes in mice. The other aim was to assess possible molecular changes in T. congolense (savannah) before, during and after transmission. Three groups of 10 mice each were used for virulence study and were infected with either the drug sensitive or drug resistant T. congolense, respectively. The results showed that the drug sensitive T. congolense in mice had a shorter mean pre-patent period of mean of 11dpi; the mice started to die early from 11dpi, thereafter the infection became chronic. The drug resistant T. congolense showed a mean pre-patent period of 15dpi and mice started to die at 23dpi after which the infection became acute until all animals died by 38dpi. Parasitaemia profiles of the two isolates in mice were significantly different. The mean values for weight and PCV were not significantly different between the two isolates, however the values of the two isolates when compared to the control PCV showed significant drop for drug resistant and no significant difference compare to drug sensitive isolate, furthermore body weight for the two isolates were significantly different compared to the control in both cases. The drug sensitive trypanosome had a 42.4% infection rate in Glossina pallidipes compared to 39.6% for drug resistant isolate. Using the polymerase chain reaction -restriction fragment length polymorphism (PCR-RFLP) there were no detectable molecular differences between the two strains but within each strain some molecular changes occurred after passage in both flies and mice. The PCR picked more positive cases than microscopy. Results indicate that there are differences in the pathogenesis of drug resistant and susceptible trypanosomes in the host which could responsible in production of various disease expression observed in the field. At the same time the drug resistant phenotype of the parasite is maintained drug cryopreservation and transmission of the trypanosomes in the flies and host thus posing a great challenge in the control of the trypanosomes using chemotherapy.