Navorsingsberig In vivo evaluation of amitraz against ticks under field conditions in Ethiopia

INTRODUCTION Ticks are widely distributed in various agro-ecological zones in Ethiopia, and are responsible for severe losses caused by the effect of tick worry, blood loss, damage to hides, the injection of toxins or through mortality or morbidity caused by the diseases they transmit, such as anaplasmosis, babesiosis, heartwater and theileriosis. Tick control in Ethiopia is based on the use of acaricides. Resistance to toxaphene (chlorinated camphene) in Boophilus decoloratus on dairy cattle and the increase in numbers of crossbred tick-susceptible cattle has necessitated the change to alternative acaricides. The organophosphate group of acaricides is widely used, while the amidine group (amitraz) has recently been registered for tick control in Ethiopia. Various authors have also demonstrated the effectiveness of amitraz against mange mites (Sarcoptes scabiei var. cameli) in camels, ticks on camels, and lice and mange in pigs. This trial was aimed at testing the efficacy and residual effect of amitraz 12.5 % (Bovitraz, Bayer AH) used as a miscible oil formulation against tick species on a dairy farm in Ethiopia. MATERIALS AND METHODS The trial was carried out from 30 November 1997 to 4 January 1998 on a private dairy farm situated in Sebeta (altitude 1900 m), 25 km west of Addis Ababa. The 92 Friesian/Zebu crossbred cattle on the farm were heavily infested with B. decoloratus; a few Amblyomma variegatum and Rhipicephalus evertsi evertsi were also observed. Organophosphates (chlorfenvinphos, quintiofos, diazinon) and carbamate (carbaryl) had been used on the farm prior to applying the test acaricide. Approximately 100 ticks were collected from the herd and identified to ascertain the tick species present in the area. Eight heifer calves aged between 6 and 8 months were selected from the herd and allocated to a treatment and a control group, each of which consisted of 4 animals. Two days before the trial commenced, the number of ticks on each of the experimental calves was counted to assess tick density. The 4 calves in the treatment group were thoroughly wetted with a hand-sprayed, freshly prepared aqueous emulsion of amitraz at the volume and concentration recommended by the manufacturer. Treatment was applied only once on Day 0 (acaricide application day). The 4 calves selected as controls were left untreated. The 2 groups of calves were ear-tagged in order to identify them and were maintained in separate tick infested camps to avoid contact between them. The numbers of ticks on each of the control and treated calves were counted 2 days before (Day –2) the commencement of the trial and on Day 0 (after treatment had been applied) and Days 1, 2, 3, 4, 7, 8, 10, 14, 17, 21, 28, and 35 post-treatment, during which process the calves were restrained and the ticks were identified in situ. Counting was facilitated by using a standard hand tally counter to ensure accuracy. The trial was discontinued when the total tick counts on the treated group started to increase. The percentage control gained was calculated by using the formula of Drummond et al.:


INTRODUCTION
Ticks are widely distributed in various agro-ecological zones in Ethiopia 7 , and are responsible for severe losses caused by the effect of tick worry, blood loss, damage to hides, the injection of toxins or through mortality or morbidity caused by the diseases they transmit, such as anaplasmosis, babesiosis, heartwater and theileriosis 2 .
Tick control in Ethiopia is based on the use of acaricides.Resistance to toxaphene (chlorinated camphene) in Boophilus decoloratus on dairy cattle and the increase in numbers of crossbred tick-susceptible cattle has necessitated the change to alternative acaricides 8 .The organophosphate group of acaricides is widely used, while the amidine group (amitraz) has recently been registered for tick control in Ethiopia.Various authors have also demonstrated the effectiveness of amitraz against mange mites (Sarcoptes scabiei var.cameli) in camels 6,9 , ticks on camels 1,5 , and lice 10 and mange in pigs 4 .
This trial was aimed at testing the efficacy and residual effect of amitraz 12.5 % (Bovitraz, Bayer AH) used as a miscible oil formulation against tick species on a dairy farm in Ethiopia.

MATERIALS AND METHODS
The trial was carried out from 30 November 1997 to 4 January 1998 on a private dairy farm situated in Sebeta (altitude 1900 m), 25 km west of Addis Ababa.The 92 Friesian/Zebu crossbred cattle on the farm were heavily infested with B. decoloratus; a few Amblyomma variegatum and Rhipicephalus evertsi evertsi were also observed.Organophosphates (chlorfenvinphos, quintiofos, diazinon) and carbamate (carbaryl) had been used on the farm prior to applying the test acaricide.
Approximately 100 ticks were collected from the herd and identified to ascertain the tick species present in the area.Eight heifer calves aged between 6 and 8 months were selected from the herd and allocated to a treatment and a control group, each of which consisted of 4 animals.Two days before the trial commenced, the number of ticks on each of the experimental calves was counted to assess tick density.The 4 calves in the treatment group were thoroughly wetted with a hand-sprayed, freshly prepared aqueous emulsion of amitraz at the volume and concentration recommended by the manufacturer.Treatment was applied only once on Day 0 (acaricide application day).The 4 calves selected as controls were left untreated.The 2 groups of calves were ear-tagged in order to identify them and were maintained in separate tick infested camps to avoid contact between them.
The numbers of ticks on each of the control and treated calves were counted 2 days before (Day -2) the commencement of the trial and on Day 0 (after treatment had been applied) and Days 1, 2, 3, 4, 7, 8, 10, 14, 17, 21, 28, and 35 post-treatment, during which process the calves were restrained and the ticks were identified in situ.Counting was facilitated by using a standard hand tally counter to ensure accuracy.The trial was discontinued when the total tick counts on the treated group started to increase.The percentage control gained was calculated by using the formula of Drummond et al.

RESULTS
Table 1 summarises the total tick counts on the treated and control groups, and the percentage control achieved by the test acaricide.Tick reduction was observed from Day 1 to Day 28 posttreatment.From Day 3 onwards 100 % control was achieved and this was maintained for at least a further 19 days.On Day 28 post-treatment, 1 experimental calf had acquired 6 ticks but the others were free from infestation.On Day 35 post-treatment all the treated calves were infested and the trial was discontinued.The treatment group had significantly fewer ticks than the control group for a period of 35 days (P < 0.05).Tick species identified during the trial were A. variegatum, B. decoloratus and R. e. evertsi, with B. decoloratus predominating.

DISCUSSION
Before the application of the test acaricide the experimental calves were heavily infested with B. decoloratus.These heavy infestations probably resulted from resistance to organophosphate and carbamate acaricides that had previously been used on the farm.After treating with amitraz, an excellent reduction in the number of ticks was observed (91 % on Day 1 to 98 % on Day 28), despite the heavy infestations present at the commencement of the trial and the continued exposure of the calves to infestation during the course of the trial.In addition, there was a rapid detachment of all tick instars from the animals treated with amitraz (Table 1), indicating that the heavy tick burdens were reduced to negligible numbers 1 day post-treatment.All treated calves were free from ticks on Day 3 post-treatment, and this trend persisted until Day 21 post-treatment.The results presented here show that a single treatment with an aqueous emulsion of amitraz, prepared and applied to calves according to the manufacturer 's recommendation, provided effective protection against ticks in the area.
3 : No. ticks in control group -No.ticks in treatment group No. ticks in control group × 100