Heartwater, a febrile septicaemia of cattle, sheep, goats and wild ungulates, is caused by Rickettsia ruminantium. Transmission is by ixodid ticks of the genus Amblyomma, which are three-host ticks.
The disease is found in semi-arid rangelands and the tick is difficult to eradicate or control. Some species are known to survive off the host up to 18 months. Nonapparent infections in certain wild antelope, in addition to range stock, are thought to provide a reservoir in bushveld areas for new generations of young ticks since infection does not pass through tick eggs. Strains of varying virulence cause subacute or acute disease with high mortality.