Ghibe river basin in Ethiopia: present situation of trypanocidal drug resistance in Trypanosoma congolense using tests in mice and PCR-RFLP.

A cross-sectional study was carried out in the Ghibe valley from August to October 2010. 411 head of cattle were sampled in eight villages for buffy coat examination (BCE) and blood spots were collected from each animal for trypanosomose diagnosis by 18S-PCR-RFLP and diminazene aceturate (DA) resistance by Ade2-PCR-RFLP. Three villages were selected in a zone where trypanosomosis control operations are currently on-going whereas the other 5 villages were located outside these control operations. Twenty-four samples (5.84%) were diagnosed positive for Trypanosoma congolense by BCE and injected in mice for further characterization. Twelve of those isolates successfully multiplied in mice and were tested by an in vivo mouse test for diminazene (DA) (10 and 20mg/kg B.W.) and isometamidium (ISM) (1mg/kg B.W.) resistance. All were shown to be resistant to both drugs at all doses. The use of the Ade2-PCR-RFLP on these isolates confirmed their DA-resistance profile. Seventy-three of the collected blood spots (17.8%) were diagnosed positive for T. congolense by 18S-PCR-RFLP of which 37 (50.7%) gave amplification products with the Ade2-PCR-RFLP. Here, 35 (94.6%) showed a resistant profile, 1 (2.7%) a sensitive profile and 1 (2.7%) a mixed profile. The data were analysed by logistic regression model and the relapsing time in mice tests was assessed using the Cox regression model. There was no significant intervention effect (P=0.83) with odds ratio equal to 1.21 when using the BCE data. 18S-PCR-RFLP test also showed no significant intervention effect (P=0.60) with odds ratio equal to 1.43. The hazard ratio of getting parasitaemic after treatment with DA at 20mg/kg B.W. compared to the control group was 0.38 which differs significantly from one (P<0.001). Relapsing time after treatment with DA 10mg/kg B.W. or ISM 1mg/kg B.W. was also significantly longer than the prepatent period of the control group. The situation of drug resistance in the Ghibe valley is further discussed.