Abstract
This dissertation describes the application of two test systems with the purpose of
examining the drug sensitivity of various T. congolense stocks in cattle originating from
the province of Kénédougou in Burkina Faso. Its objective was to establish and validate
the Standard Mouse Test (in-vivo test) and the Drug Incubation Infectivity Test (a
combination of in-vivo und in-vitro test) for T. congolense with the help of T. congolense
reference clones and, using these assays, to examine drug susceptibility of various T.
congolense stocks with respect to isometamidium chloride (Samorin ®, Trypamidium ®)
and diminazene aceturate (Berenil ®). The T. congolense stocks originated from primary
isolates collected in both former projects in Samorogouan and from field studies that
examined the impact of drug resistance on the productivity of domestic livestock
(Research project ?epidemiology of drug resistance of animal trypanosomes in West
Africa?, BMZ Special Project).
Four T. congolense reference clones (IL 1180, IL 2642, IL 3000, IL 3338) with known
isometamidium and diminazene sensitivity were evaluated in the Standard Mouse Test
(SMT) and Drug Incubation Infectivity Test (DIIT). Concentrations of 1 mg/kg in the SMT
and 50 ng/ml in the DIIT (reference values) were shown to be effective to differentiate
between isometamidium-sensitive and isometamidium-resistant T. congolense clones.
For diminazene concentrations of 14 mg/kg in the SMT and 5 µg/ml in the DIIT could
distinguish between diminazene-sensitive and diminazene-resistant T. congolense
clones. For the clone IL 2642 no classification was possible with respect to diminazene in
both assays, SMT and DIIT.
Sixteen different T. congolense stocks from primary isolates originating from the province
of Kénédougou were examined in the SMT and the DIIT, and characterised with the help
of the evaluated reference values of drug-resistant and drug-sensitive T. congolense
clones. With the exception of one stock (SA 53) all examined T. congolense populations
in the SMT and the DIIT were resistant both with respect to isometamidium and (as far as
examined) with respect to diminazene.
Four of the T. congolense stocks (SA 53, SA 267, SA 268 and SA 95) originated from the
village of Samorogouan in Kénédougou and had been isolated from cattle between 1982
and 1998. The isometamidium and diminazene resistance of these trypanosome
populations found in Mastomys were comparable with published drug sensitivities in
cattle. It could be demonstrated that resistant trypanosome populations were present in
Samorogouan during an examination period of 16 years.
Twelve T. congolense stocks originated from the research project ?epidemiology of drug
resistance of animal trypanosomes in West Africa? (BMZ Special Project). Four of these
trypanosome populations (DRI 18, SRI 92, SBA 1640 and SBA 1642) had been isolated
in the cross-sectional study in 1998 and were both isometamidium- and
diminazene-resistant in the SMT and the DIIT. The other eight examined T. congolense
stocks originated from the block-treatment study (1998-1999). Three of these (MBI 2050,
TBU 2130, SRI 2179) were collected from cattle, for which the isometamidium
block-treatment had been successful. Hence it was assumed that these stocks were
isometamidium-sensitive. However in the SMT and DIIT they were characterised as
isometamidium-resistant. Apparently the parasitological detection method ?Buffy Coat
Technique?, which had been used in the field trials, was not sensitive enough to detect
trypanosome infections following isometamidium block-treatment.
The results of this study show that both assays examined, the Standard Mouse Test and
the Drug Incubation Infectivity Test, are suitable for the evaluation of drug sensitivity of T.
congolense. With the exception of one clone (IL 2642) and one T. congolense stock (SA
53), whose sensitivity for diminazene could not be classified, all examined T. congolense
reference clones and stocks could be characterised with respect to their isometamidium
and diminazene sensitivity. A comparison of both tests showed that the results of the
SMT corresponded with the results of the DIIT. T. congolense clones and stocks that
were drug-sensitive in the SMT showed a reduced infectivity for Mastomys in the DIIT
whereas trypanosome clones and stocks that were drug-resistant in the SMT retained
their infectivity for Mastomys in the DIIT. Due to its in-vitro phase the DIIT is very
laborious. For an evaluation of multiple T. congolense stocks the SMT is more simple and
practicable in use. Prior to the introduction of a pure in-vitro test that can be applied on a
routine basis the SMT is the more suitable assay for the evaluation of drug sensitivity for
T. congolense. |
