Heartwater has been transmitted experimentally by 12 Amblyomma species. Their importance depends on the extent of their distribution, adaptation to domestic stock and their efficacy as vectors. Except for one report of transovarial transmission, transmission is transstadial. Ticks may obtain the infection while feeding on reacting animals, subclinically infected hosts or perhaps on immune animals after reinfection. There is a marked increase in the infectivity of infected ticks during feeding but this decreases before and during moulting. The demonstration of Cowdria ruminantium in salivary glands of ticks suggests that transmission takes place via the saliva and that regurgitation from the gut may not be as important as previously thought. Transmission takes place on the 2nd day from the time infected nymphae were placed on the animals and on the 4th-day in the case of adult ticks.