Relapsing Trypanosoma vivax infections in Nigerian zebu cattle treated with diminazine aceturate

A T. vivax infection was syringe passaged in a series of animals and exposed to various levels of treatment with diminazine. The original mixed infections were highly pathogenic but only T. vivax relapsed following treatment at the level of 3·5 mg/kg. and at this stage the infection was less pathogenic than later. Following two additional sub-curative treatments of 1·75 and 3·5 mg/kg. and seven serial passages followed by three successive sub-curative exposures to 10·5 mg/kg. infections were obtained which eventually relapsed to 14 mg/kg. Relapse intervals bore little relationship to the size of the sub-curative dose. They lengthened progressively in the relatively few animals which eventually became only periodically parasitaemic or aparasitaemic. There was no extension beyond 48 hours of the time taken for progressively tolerant infections to become aparasitaemic nor was there any shortening of the relapse intervals following initial treatment of more tolerant infections at lower levels. © 1970 E. & S. Livingstone.