The control of heartwater on large-scale commercial and smallholder farms in Zimbabwe

As part of a series of studies associated with the development of improved vaccines for heartwater (a tick-borne disease of ruminant livestock caused by Cowdria ruminantium), field surveys were carried out to assess losses as sociated with the disease and the costs associated with controlling it in t he two main agro-ecological zones of Zimbabwe (lowveld and highveld) where heartwater is believed to be endemic and epidemic, respectively. In each zo ne, a cross-sectional study was performed in the main farming systems (smal lholder (SH) and large-scale commercial (LSC) beef and dairy), followed by longitudinal studies in the same sectors to improve data accuracy for some parameters. Suspected heartwater-specific mortality in cattle was similar i n all LSC sectors (p = 0.72) accounting for a median 1% mortality risk. Hea rtwater-specific mortality in SH areas was not assessed due to poor diagnos tic ability of the farmers. Few LSC farms and SH households kept sheep; sus pected heartwater-specific mortality in LSC sheep was 0.8% in the lowveld a nd 2.4% in the highveld. Goats were a major enterprise in SH areas but not on LSC farms. Suspected heartwater mortality in LSC goats was 0.8% at one s ite in the highveld and 17.5% on a farm in the lowveld. Application of acar icides was the major control method for heartwater and other tick-borne dis eases on both SH and LSC farms. On LSC farms, plunge dipping was used most frequently and the number of acaricide applications ranged widely between 3 and 52 per year. The total cost of acaricides per head per annum was highe r in highveld dairies than in highveld and lowveld beef enterprises (p = 0. 03). In SH areas, cattle plunge dipping was conducted by the government wit h an average frequency of 8 +/- 2 (sd) immersions per annum in both the low veld and highveld. The type of tick control on sheep and goats in all produ ction systems was highly variable (ranging from none to hand removal or int ensive acaricide treatment). Suspected heartwater cases on LSC farms were t reated with tetracyclines; treatment was not reported in SH areas. Reported treatment costs were high (median Z$ 120) and highly variable (range Z$4-8 33). Vaccination against heartwater with the live, blood-based vaccine was reported on only one LSC farm. LSC farms applying acaricide 30 or more time s per year reported higher morbidity (p < 0.0001) and mortality (p < 0.0001 ) than farms applying acaricides less than 30 times a year. This finding su pports the use of reduced tick control in the management of heartwater in Z imbabwe. (C) 1999 Elsevier Science B.V. All rights reserved.