Identification of drugs effective against Cowdria ruminantium using a mouse screening system.

Heartwater is a tick-transmitted rickettsial infection of ruminants, caused by Cowdria ruminantium. The tetracyclines are the only compounds available for therapy of the disease. A screen, using mice infected with C. ruminantium, was developed and used to identify new compounds with potential for the control of heartwater. A series of di-4-methyl-thiosemicarbazones was shown to be highly active in the mouse model and their efficacy was confirmed in further trials in sheep infected with C. ruminantium. The mouse screen was shown to be simple to operate and reliably predictive of activity against heartwater. Ways in which the screen may be improved are suggested.