The tick vectors of Cowdria ruminantium (Ixodoidea, Ixodidae, genus Amblyomma) and their distribution.
Twelve species of Amblyomma are presently known to be capable of transmitting C. ruminantium; of these, A. variegatum is the most important and widely distributed vector in Africa. It has also extended its range considerably outside this continent, eastwards to the Yemen and to the islands of Madagascar, Réunion and Mauritius, and westwards to the Cape Verde islands and to some of the Caribbean islands. A. hebraeum is probably the only field vector in most parts of southern Africa. A 3rd species, A. lepidum, is known to have been involved in field outbreaks of heartwater in the Sudan. Two other species are also currently regarded as field vectors of Cowdria: A. astrion on the islands of São Tomé and Principe, and A. pomposum in Angola. Another 5 African species (A. cohaerens, A. gemma, A. tholloni, A. sparsum and A. marmoreum) have proved to be capable of transmitting heartwater in the laboratory, as have 2 American species (A. maculatum and A. cajennense), but none of these ticks have been implicated in field outbreaks of the disease.