THE ROLE OF HYALOMMA TICKS IN FOOT INFESTATIONS AND TEMPORARY LAMENESS OF SHEEP IN A SEMIARID REGION OF SOUTH-AFRICA

An outbreak of lameness amongst Merino lambs, associated with the pres ence of Hyalomma ticks, was investigated on a farm in the south-wester n Free State, South Africa. The purpose was to follow the progress of the condition and to determine the extent of involvement of the two Hy alomma species which occur in the region. The flock of experimental sh eep (n = 460) ranged free in natural veld under extensive farming cond itions. During September and October 1993, adult ewes and lambs in thi s flock were examined at weekly intervals to determine tick identity, abundance and attachment-site preferences on lame and unaffected anima ls. Lameness occurred only among lambs, of which 68 were affected duri ng the 8-week period. Hyalomma ticks tended to aggregate and mean numb ers of ticks/aggregation were significantly higher on lame lambs ((x) over bar = 11,3) than on either the unaffected lambs ((x) over bar = 6 ,9) or the ewes ((x) over bar = 7,1). Most tick aggregations (72,4%) o n the lame lambs occurred on the lower legs and feet, 34 out of 55 of these on the fetlocks or interdigital clefts. Hyalomma truncatum domin ated (>97%) on all animals examined. Only 15,8% of the Hyalomma margin atum rufipes recovered from the lame animals were attached to the legs . At two other localities at which H. marginatum rufipes was more abun dant, or even dominant, few ticks attached to the lower legs or feet. Those that did were mostly H. truncatum (>90%). Both H. marginatum ruf ipes and H. truncatum may attach to the same ventral and anogenital bo dy regions, but H. truncatum has a tendency to attach also to the feet and lower legs. Although attachment of one or a few ticks in the axil lar region or upper legs may cause lameness in sheep, the attachment o f ticks to the interdigital clefts and fetlocks almost always causes l ameness. The latter condition is more likely to occur in regions where H. truncatum dominates.