Efficacy of fipronil against Amblyomma hebraeum ticks on boer goats and detection of Ehrlichia ruminantium in ticks in Limpopo Province, South Africa

Abstract

Heartwater, caused by Ehrlichia ruminantium, causes significant economic losses to commercial small stock farmers, including commercial boer goat farmers in the Limpopo Province of South Africa. Heartwater is endemic in this region where Amblyomma hebraeum, the South African bont tick and the vector for this disease occurs. Due to their long mouthparts and specific attachment sites on goats, A. hebraeum is also associated with wounds, secondary abscess formation and lameness. Small stock farmers in the Limpopo Province employ various methods to control A. hebraeum and the negative effects associated with this tick, including heartwater. Two approaches where followed to focus on the control of A. hebraeum on the one hand and the detection and cryo-preservation of E. ruminantium from A. hebraeum on the other hand. The aim of this study was therefore twofold. By firstly determining the efficacy of a 1.0% fipronil pour-on solution against A. hebraeum by performing a therapeutic- and persistent efficacy trial and secondly to detect and cryo-preserve E. ruminantium from A. hebraeum ticks from a heartwater endemic region in the Limpopo province of South Africa. It was demonstrated that a 1.0% fipronil pour-on solution is 100% effective and has a persistent efficacy of seven days against A. hebraeum, but only if a targeted treatment approach is followed whereby the pour-on solution is applied to the predilection sites of A. hebraeum. A 1.0% fipronil pour-on solution can therefore be used by boer goat farmers to control A. hebraeum and the negative effects associated with this tick. In order to detect and cryo-preserve E. ruminantium from A. hebraeum ticks, ground-up-tick-supernatant samples were prepared in the laboratory from A. hebraeum ticks collected from goats and cattle at specified time intervals. To determine whether E. ruminantium was present in A. hebraeum ticks, DNA extraction, nested PCR of the pCS20 region of the E. ruminantium genome and demonstration of the amplified DNA by agarose gel electrophoresis was performed. The results demonstrated that E. ruminantium was indeed present in eight out of eight ground-up-tick-supernatant samples that were cryo-preserved. In future research, these samples may become very useful for isolating current strains of heartwater, which will ultimately lead to a better understanding of the disease and to facilitate the implementation of novel control methods.