Distributions of the vectors of heartwater, Amblyomma hebraeum and Amblyomma variegatum (Acari : Ixodidae), in Zimbabwe

The tick vectors of heartwater (Cowdria ruminantium infection) in Zimbabwe, Amblyomma hebraeum and Amblyomma variegatum, historically were believed to be confined to the low lying regions of the south and north-west of the co untry. However, country-wide surveys performed in 1975-1980 and 1988-1991 d emonstrated that both species were also established in western parts of the highveld plateau and had started to encroach on the predominantly heartwat er-free central and eastern highveld regions. To determine the current dist ributions of both the vectors and evaluate the potential threat of heartwat er to animals in the highveld, a survey of ticks infesting cattle was perfo rmed in 1996 at 2994 locations in small-holder and large-scale commercial f anning areas throughout Zimbabwe. Amblyomma hebraeum was collected at 1329 locations, A. variegatum at 72 locations and both A. hebraeum and A. varieg atum at 13 locations. The results demonstrated that A. hebraeum was present , as previously recorded, throughout the southern half of the country and a ppeared to have undergone further limited spread into the central and easte rn highveld regions. Only the northern-most region of the country appeared to be free of this species. Amblyomma variegatum was collected mainly in th e north-west, as previously recorded, but was also found at isolated locati ons across the central highveld region and along the eastern border with Mo zambique. This species was, however, still absent from the southern half an d the northern-most regions of the country. An overlap of the distributions of the two species existed within a zone along the southern and eastern re gions of the distribution of A. variegatum. These results suggest that the vectors of heartwater are spreading and threaten to introduce heartwater in to intensive livestock-producing regions of the country. Exp Appl Acarol 22 : 725-740 (C) 1998 Kluwer Academic Publishers.