RESPONSE OF DIMINAZENE-RESISTANT AND DIMINAZENE-SUSCEPTIBLE TRYPANOSOMA-CONGOLENSE TO TREATMENT WITH DIMINAZENE WHEN OCCURRING AS A MIXED INFECTION IN GOATS

A study was carried out to determine whether a drug-resistant trypanos ome population could influence the survival of a drug-sensitive popula tion in mixed infections in goats. To identify both populations during the course of a mixed infection, a system for distinguishing them was developed; using a nucleotide sequence of a cDNA that was derived fro m Trypanosoma congolense ILNat 3.3 (IL 1616), a pair of 20-mer primers was designed which, in a PCR, amplified a 900-bp sequence from the di minazene-sensitive trypanosome, T. congolense IL 1180, but not the dim inazene-resistant trypanosome, T. congolense IL 3247. The PCR techniqu e detected 100 pg of IL 1180 DNA when mixed with 25 ng of total genomi c DNA of IL 3274, as determined by gel electrophoresis and ethidium br omide-staining of the PCR products. Using the 900-bp PCR product as a P-32-labelled probe on Southern blots, the sensitivity was increased 1 00-fold. Three groups of five goats each were infected with IL 1180 (g roup A), IL 3274 (group B) or both clones simultaneously (group C), an d treated with diminazene aceturate at a dose of 7.0 mg/kg body weight following detection of trypanosomes. Three other groups of three goat s each were similarly infected and kept as untreated controls. All gro up A animals were cured, while all in group B and four animals in grou p C relapsed. Trypanosomes were harvested from all animals at regular intervals up to 60 days post treatment. Using the PCR techniques, IL 1 180 DNA could not be detected in any post-treatment trypanosome DNA sa mple. It therefore appeared, on the basis of the sensitivity of the DN A detection systems used, that IL 1180 is unable to survive treatment with diminazene aceturate when mixed with IL 3274 in goats.