Comparison of the antitheilerial effect of Wellcome 993C and halofuginone

The efficacy of Wellcome compound 993C and halofuginone was compared using cattle artificially infected with Theileria parva and using in vitro cultures of T parva. At a total dose of 20 mg/kg administered by the intramuscular route, 993C cured all nine cattle of advanced theileriosis and no major recrudescences of the infection occurred. Halofuginone was given by mouth at 1.2 mg/kg and cured five cattle of early clinical theileriosis, but significant recrudescences of infection occurred. Halofuginone at 1.2 mg/kg cured a further five out of six cattle with advanced theileriosis, but four of the five survivors developed moderate to severe resurgences of infection. The dose of 20 mg/kg of 993C was known to be close to its effective level, but 1.2 mg/kg halofuginone, the dose used by earlier workers, may not have been adequate. All 10 untreated control cattle died of acute theileriosis. The in vitro EC50 of both compounds was 0.003 mg per litre but, whereas the dose response curve of 993C was sigmoid, that of halofuginone was bellshaped. This may reflect toxicity to the host lymphoblastoid cells with higher concentrations of halofuginone.