The distribution of heartwater in the highveld of Zimbabwe, 1980-1997.

Heartwater, the tick-borne disease caused by the rickettsia Cowdria ruminantium has historically been confined to the southern and western lowvelds of Zimbabwe. Since 1986, however, cases of heartwater have been diagnosed with increasing frequency in the central and eastern regions of the previously heartwater-free highveld plateau. During the same period, collections of the two major tick vectors of heartwater in Zimbabwe, Amblyomma hebraeum and Amblyomma variegatum, were made for the first time in these areas, suggesting that spread of these ticks was responsible for the changed distribution of the disease. The factors associated with this spread have not been determined, but increased cattle and wildlife movement and reduced intensity of dipping undoubtedly play important roles. Currently, the distribution of heartwater and its vectors in the highveld is still largely restricted to the central and eastern regions. The northern regions of the highveld appear to be predominantly uninfected, though it is likely that, eventually, heartwater will spread further with considerable impact on livestock production in Zimbabwe.