Acta Tropica, 52(1992)129-133
129
© 1992 Elsevier Science Publishers B.V. All rights reserved 0001-706X/92/$05.00 ACTROP 00243
The efficacy of ethion EC (1010 g/l) against cattle ticks in M orogoro, Tanzania R.D. Mosha and Per Schyum Faculty of Veterinary Medicine, Sokoine University of Agriculture, P.O. Box 3017, Morogoro, Tanzania. (Received 27 April 1992; accepted 5 August 1992) Ethion, an organophosphorus insecticide/acaricide, was found to be effective against the various cattle ticks present in Morogoro Tanzania after it was sprayed on cattle twice weekly for 1 year. The pre- and post-replenishment concentrations of ethion ranged between 0.04 and 0.05%. Ethion was found to be stable in the spraywash. The good efficacymakes ethion a good alternative to dioxathion in tick control in Tanzania. Key words: Ethion; Efficacy;Ticks; Tanzania
Introduction Ethion (O,O,O',O'-tetraethyl-S,S'-methylene bisphosphorodithioate) is an organosp h o s p h o r u s c o m p o u n d (OP) used both as an acaricide and as an insecticide. As an insecticide it controls scale insects, leaf miners and leaf hoppers on citrus, vegetables, apples and grapes (Cheminova, 1986). As an acaricide it has been used against Boophilus microplus ticks in Australia and in South America at a concentration o f 0.075% (Nunez et al, 1985; Palmer, 1976). Being an acaricide/insecticide, ethion, like other OPs, provides an alternative to the organochlorine insecticides (OCs), particularly where insects or ticks have developed resistance to OCs or where OCs are deemed too persistent to be used. In Tanzania, unlike Australia and South America, various species o f ticks are present and are responsible for transmission o f various diseases. The ticks are Rhipicephalus appendiculatus which transmits East Coast Fever and Boophilus decoloratus which transmits Babesiosis and Anaplasmosis. Other ticks are Amblyomma spp. (transmits heartwater) Hyalomma spp. (transmits sweating sickness) and Rhipicephalus evertsi (transmits Babesiosis). A l t h o u g h ethion has been used effectively against Boophilus spp. in Australia and South America, information on its efficacy against the various species o f ticks in Tanzania is scanty. It was therefore the purpose o f the present work to determine the efficacy of ethion against the various cattle ticks present in M o r o g o r o , Tanzania. The pre- and postreplenishment concentrations o f the dipping mixture were also determined for a period o f 1 m o n t h during the efficacy trials.
Correspondenee to." R.D. Mosha, Faculty of Veterinary Medicine, Sokoine University of Agriculture, P.O. Box 3017, Morogoro, Tanzania.
130
Materials and Methods
Location The trials were conducted at the Sokoine University of Agriculture farm, which has about 300 dairy cattle at any one moment. The sprayrace, whose tank has 2000 litres, is powered by a diesel engine and has the ability to spray about 250 cattle per h. The trial was conducted from June 1990 to June 1991. The year usually has two rainy seasons - - the short and long rainy seasons separated by a dry season.
Preparation of ethion spray solution Ethion emulsifiable concentrate 1010 g/1 (ethion EC 1010 g/l) was generously supplied by Cheminova Agro Company of Denmark. 1 litre of this ethion preparation was diluted to 2000 litres by water to fill the spray-race tank. The replenishment rate was 0.5 litre of ethion EC 1010 g/1 for every 1000 litres of water added. Then a boosting up was done by adding 40 ml of ethion EC 1010 g/1 to the spray-tank for every 100 cattle that were to be sprayed.
Analysis of spray mixtures for ethion concentration Sampling The spray-tank was usually emptied after l l½ months by mechanical pumping out of the water. After one such emptying, the fluctuation of ethion levels pre- and post-replenishment was followed up for a period of 1 month. This was performed by sampling the initial refilled mixture after the emptying (refilling rate, ! litre ethion EC 1010 g/1:2000 litres water), the subsequent pre- and post-replenishment mixtures and also the mud-layer at the bottom after the next emptying. The samples were packed in leak-proof containers and sent to Cheminova Agro Company of Denmark for gas chromatographic analysis of ethion concentration.
Gas chromatography Ethion was extracted from the spraywash sample using acetonitrile and quantified by a Hewlett Packard HP 5890 Series II gas chromatograph using the external standard method whereby purified ethion acted as reference material. The chromatograph was equipped with flame ionization detector, a capillary on-column injection system with programmable pressure and autoinjection. Chromatographic conditions were as follows. Column: Hewlett Packard HP1, methylsilicone, cross-linked, 5 m long, 0.32 mm i.d., 2.65 I~m film thickness. Temperature: column 200°C (isothermal), injector 200°C (on-column), detector 300°C. Carrier gas: helium with the following pressure programme: initial pressure 2.5 psi, initial time 2 rain, rate 1.0 psi/rain, final pressure 6.5 psi, final time 0 min. The retention time for ethion was 3.3 min, while its detection limit was 0.005%.
Rainfall A record of the rainfall during the trial period was obtained from Sokoine University Meteorological Station. The aim was to find out whether there was any tick-borne disease outbreak associated with rainfall.
131
Monitoring of ticks and tick-borne diseases A record o f ticks a n d t i c k - b o r n e diseases affecting the cattle in the University farm was m a i n t a i n e d d u r i n g the trial period.
Results N o clinical sign o f o r g a n o p h o s p h o r u s toxicity was o b s e r v e d in a n y o f the s p r a y e d animals.
Spray-wash concentrations The c o n c e n t r a t i o n s o f ethion in the v a r i o u s samples o f the s p r a y w a s h pre- a n d p o s t r e p l e n i s h m e n t are seen in Table 1, from which it can be seen that, at the given rate o f replenishment, the s p r a y w a s h was m a i n t a i n e d at a m o r e or less c o n s t a n t c o n c e n t r a t i o n ranging m a i n l y between 0.04 a n d 0.05% w/w. The m u d l a y e r which was s a m p l e d h a d a v o l u m e o f a b o u t 15 litres; so the c o n c e n t r a t i o n o f 0.79% (w/w) a m o u n t s to a b o u t 0.12 kg o f ethion in total, which is a very low a m o u n t ( a b o u t 2.3% o f the total ethion used for the m o n t h ) , t a k i n g into c o n s i d e r a t i o n that a b o u t 3000 cattle were s p r a y e d d u r i n g the m o n t h o f s p r a y w a s h sampling.
Rainfall The m o n t h l y rainfall d i s t r i b u t i o n d u r i n g the trial p e r i o d is shown in Fig. 1, which shows two rainfall seasons - - N o v e m b e r 1990 to J a n u a r y 1991 a n d M a r c h 1991 to M a y 1991, with p e a k rains in N o v e m b e r a n d April. T h e r e were no o u t b r e a k s o f t i c k - b o r n e diseases associated with the rainfall peaks.
TABLE 1 Pre- and postreplenishment concentrations of ethion in spraywash Date
[4 Dec. 1990 18 Dec. 1990 21 Dec. 1990 26 Dec. 1990 29 Dec. 1990 2 Jan. 1991 5 Jan. 1991 9 Jan. 1991 12 Jan. 1991 15 Jan. 1991 18 Jan. 1991
Replenishment
Concentration of spraywash (%, w/w)
water added (litres)
ethion added (ml)
prereplenishment
postreplenishment
2000 930 345 645 765 965 750 750 720 525
1000 585 293 443 503 503 495 495 480 383
-" 0.04 0.04 0.05 0.06 0.05 0.05 0.05 0.05 0.05
0.05 0.04 0.05 0.05 0.05 0.04 0.04 0.05 0.05 0.05
aTank emptied and refilled. bConcentration of ethion in mud-layer.
0.79 b
132 220
210 200 190 180 170 160
150 140 130
E v
120
-4,
110
z
100 9O 8O 7O 6O
5O 40 30
2O 10 0 JUN
JUL
AUG
SEP
OCT
NOV
DEC
MONTH
1
JAN
FEB
,^^^^,
MAR
APR
MAY
JUN
Fig. 1. Monthly rainfall distribution at Sokoine University of Agriculture, June 1990 to June 1991.
Ticks and tick-borne diseases (TBD) Until the start of the trial, toxaphene (an OC) was used in the spray-race. On the first day of the trial, all animals were examined and found to be moderately infested with ticks (0 5 ticks per animal); most of these ticks were Rhipicephalus spp. or Boophilus decoloratus. After spraying twice with ethion all the ticks were eliminated. Regular examination of the animals after every spraying showed that ticks reappeared on the animals on the 2nd or 3rd day after spraying. The T B D observed during the trial were: 2 cases of East Coast fever (July 1990) and four cases of anaplasmosis distributed as follows: 2 cases in August 1990, one case in November 1990 and one case in December 1990. From January 1991 to June 1991 no case of T B D was observed.
Discussion The fact that none of the animals during the trial showed any signs of toxicity was not unexpected, because the dose of 0.05% used was smaller by far than the maximum non-toxic dermal dose of 0.25% (w/w) recorded for ethion on cattle (Osweiler et al., 1985). The manifestation of toxicity has been observed in goats when a dermal dose of 100 mg/kg was applied (Mosha et al., 1990). The 100 mg/kg dose was about double the 0.25% dermal dose assuming that about 1 litre of the 0.25% dipwash is enough for a 50 kg goat. The trial shows that ethion EC at the concentration of 0.04 0.05% was effective in controlling the various ticks present in the University farm and hence the tickborne diseases. The few tick-borne diseases recorded may be attributed to inexperience in the use of the acaricide, particularly at the beginning of the trial. Tick-borne
133 diseases would easily occur if the animals did not stay in the spray race long enough to be effectively covered by the acaricide. This is believed to be the cause o f the two early cases o f East Coast fever and anaplasmosis. For the two cases o f anaplasmosis which occurred in N o v e m b e r December, 1990, similar reasons m a y be advanced. Furthermore, as the period was a rather rainy one (Fig. 1) the possibility exists that the acaricide was washed from the animals b o d y by rain immediately after spraying. Washing off o f acaricide from the animal's b o d y by water (rain water or other source o f water) is one o f the possible reasons for early occurrence o f tick-borne diseases despite strict adherence to the dipping regime (Cooper, 1980). The efficacy results obtained agree with those achieved by Mbise 1987 (unpublished results), who in his laboratory and field trials in Arusha - - an area o f a higher altitude than M o r o g o r o in Tanzania - - found ethion a suitable acaricide in the control o f various ticks present in the area, i.e., Rhipicephalus appendiculatus, Rhipicephalus evertsi, Boophilus decoloratus and Amblyomma variegatum. On comparing the efficacy o f ethion and dioxathion, which is another OP, Mbise found that ethion had slightly better efficacy than dioxathion. In view o f this good efficacy, ethion forms a good alternative to dioxathion in controlling ticks in Tanzania, especially where OCs like toxaphene have been withdrawn because o f tick resistance. The results obtained in M o r o g o r o and Arusha, Tanzania agree with those previously obtained in Australia and South America, where ethion has been used against one species o f tick only, i.e., Boophilus microplus (Nunez et al., 1985; Palmer, 1976). The concentrations o f ethion in the sprayrace tank appear to be almost constant. This agrees with the view by N u n e z et al. (1985) that ethion mixtures in dip tanks are quite stable.
Acknowledgements We thank M r Peter Jingu for technical help and Miss Jescar Mkami for typing the manuscript.
References Cheminova (1986) Data Manual -- Ethion Technical. Cooper Company (1980) The control of cattle ticks in East and Central Africa. 4tl~ Edn. Wellcome Eastern Africa Ltd. Kabete, Kenya. Mosha, R.D., Gyrd-Hansen, N. and Nielsen, P. (1990) Fate of ethion in goats after intravenous, oral and dermal administration. Pharmacol. Toxicol. 67, 246 251. Nunez, J.L., M unoz-Cobenas, M.E. and Moltedo, H.L. (1985) Boophilusmicroplus.The Common Cattle Tick, p. 94-152, Springer, Berlin. Osweiler, G.D., Carson, T.L., Buck, W.B. and Van Gelder, G.A. (1985) Clinical and Diagnostic Veterinary Toxicology, 3rd Edn. p. 275 320, Kendall/Hunt, Dubuque. Palmer, W.A. (1976). Management of ethion-chlordimeform mixtures in dipping baths. Department of Agriculture, New South Wales Tech. Bull. 9, 1 11.
129
© 1992 Elsevier Science Publishers B.V. All rights reserved 0001-706X/92/$05.00 ACTROP 00243
The efficacy of ethion EC (1010 g/l) against cattle ticks in M orogoro, Tanzania R.D. Mosha and Per Schyum Faculty of Veterinary Medicine, Sokoine University of Agriculture, P.O. Box 3017, Morogoro, Tanzania. (Received 27 April 1992; accepted 5 August 1992) Ethion, an organophosphorus insecticide/acaricide, was found to be effective against the various cattle ticks present in Morogoro Tanzania after it was sprayed on cattle twice weekly for 1 year. The pre- and post-replenishment concentrations of ethion ranged between 0.04 and 0.05%. Ethion was found to be stable in the spraywash. The good efficacymakes ethion a good alternative to dioxathion in tick control in Tanzania. Key words: Ethion; Efficacy;Ticks; Tanzania
Introduction Ethion (O,O,O',O'-tetraethyl-S,S'-methylene bisphosphorodithioate) is an organosp h o s p h o r u s c o m p o u n d (OP) used both as an acaricide and as an insecticide. As an insecticide it controls scale insects, leaf miners and leaf hoppers on citrus, vegetables, apples and grapes (Cheminova, 1986). As an acaricide it has been used against Boophilus microplus ticks in Australia and in South America at a concentration o f 0.075% (Nunez et al, 1985; Palmer, 1976). Being an acaricide/insecticide, ethion, like other OPs, provides an alternative to the organochlorine insecticides (OCs), particularly where insects or ticks have developed resistance to OCs or where OCs are deemed too persistent to be used. In Tanzania, unlike Australia and South America, various species o f ticks are present and are responsible for transmission o f various diseases. The ticks are Rhipicephalus appendiculatus which transmits East Coast Fever and Boophilus decoloratus which transmits Babesiosis and Anaplasmosis. Other ticks are Amblyomma spp. (transmits heartwater) Hyalomma spp. (transmits sweating sickness) and Rhipicephalus evertsi (transmits Babesiosis). A l t h o u g h ethion has been used effectively against Boophilus spp. in Australia and South America, information on its efficacy against the various species o f ticks in Tanzania is scanty. It was therefore the purpose o f the present work to determine the efficacy of ethion against the various cattle ticks present in M o r o g o r o , Tanzania. The pre- and postreplenishment concentrations o f the dipping mixture were also determined for a period o f 1 m o n t h during the efficacy trials.
Correspondenee to." R.D. Mosha, Faculty of Veterinary Medicine, Sokoine University of Agriculture, P.O. Box 3017, Morogoro, Tanzania.
130
Materials and Methods
Location The trials were conducted at the Sokoine University of Agriculture farm, which has about 300 dairy cattle at any one moment. The sprayrace, whose tank has 2000 litres, is powered by a diesel engine and has the ability to spray about 250 cattle per h. The trial was conducted from June 1990 to June 1991. The year usually has two rainy seasons - - the short and long rainy seasons separated by a dry season.
Preparation of ethion spray solution Ethion emulsifiable concentrate 1010 g/1 (ethion EC 1010 g/l) was generously supplied by Cheminova Agro Company of Denmark. 1 litre of this ethion preparation was diluted to 2000 litres by water to fill the spray-race tank. The replenishment rate was 0.5 litre of ethion EC 1010 g/1 for every 1000 litres of water added. Then a boosting up was done by adding 40 ml of ethion EC 1010 g/1 to the spray-tank for every 100 cattle that were to be sprayed.
Analysis of spray mixtures for ethion concentration Sampling The spray-tank was usually emptied after l l½ months by mechanical pumping out of the water. After one such emptying, the fluctuation of ethion levels pre- and post-replenishment was followed up for a period of 1 month. This was performed by sampling the initial refilled mixture after the emptying (refilling rate, ! litre ethion EC 1010 g/1:2000 litres water), the subsequent pre- and post-replenishment mixtures and also the mud-layer at the bottom after the next emptying. The samples were packed in leak-proof containers and sent to Cheminova Agro Company of Denmark for gas chromatographic analysis of ethion concentration.
Gas chromatography Ethion was extracted from the spraywash sample using acetonitrile and quantified by a Hewlett Packard HP 5890 Series II gas chromatograph using the external standard method whereby purified ethion acted as reference material. The chromatograph was equipped with flame ionization detector, a capillary on-column injection system with programmable pressure and autoinjection. Chromatographic conditions were as follows. Column: Hewlett Packard HP1, methylsilicone, cross-linked, 5 m long, 0.32 mm i.d., 2.65 I~m film thickness. Temperature: column 200°C (isothermal), injector 200°C (on-column), detector 300°C. Carrier gas: helium with the following pressure programme: initial pressure 2.5 psi, initial time 2 rain, rate 1.0 psi/rain, final pressure 6.5 psi, final time 0 min. The retention time for ethion was 3.3 min, while its detection limit was 0.005%.
Rainfall A record of the rainfall during the trial period was obtained from Sokoine University Meteorological Station. The aim was to find out whether there was any tick-borne disease outbreak associated with rainfall.
131
Monitoring of ticks and tick-borne diseases A record o f ticks a n d t i c k - b o r n e diseases affecting the cattle in the University farm was m a i n t a i n e d d u r i n g the trial period.
Results N o clinical sign o f o r g a n o p h o s p h o r u s toxicity was o b s e r v e d in a n y o f the s p r a y e d animals.
Spray-wash concentrations The c o n c e n t r a t i o n s o f ethion in the v a r i o u s samples o f the s p r a y w a s h pre- a n d p o s t r e p l e n i s h m e n t are seen in Table 1, from which it can be seen that, at the given rate o f replenishment, the s p r a y w a s h was m a i n t a i n e d at a m o r e or less c o n s t a n t c o n c e n t r a t i o n ranging m a i n l y between 0.04 a n d 0.05% w/w. The m u d l a y e r which was s a m p l e d h a d a v o l u m e o f a b o u t 15 litres; so the c o n c e n t r a t i o n o f 0.79% (w/w) a m o u n t s to a b o u t 0.12 kg o f ethion in total, which is a very low a m o u n t ( a b o u t 2.3% o f the total ethion used for the m o n t h ) , t a k i n g into c o n s i d e r a t i o n that a b o u t 3000 cattle were s p r a y e d d u r i n g the m o n t h o f s p r a y w a s h sampling.
Rainfall The m o n t h l y rainfall d i s t r i b u t i o n d u r i n g the trial p e r i o d is shown in Fig. 1, which shows two rainfall seasons - - N o v e m b e r 1990 to J a n u a r y 1991 a n d M a r c h 1991 to M a y 1991, with p e a k rains in N o v e m b e r a n d April. T h e r e were no o u t b r e a k s o f t i c k - b o r n e diseases associated with the rainfall peaks.
TABLE 1 Pre- and postreplenishment concentrations of ethion in spraywash Date
[4 Dec. 1990 18 Dec. 1990 21 Dec. 1990 26 Dec. 1990 29 Dec. 1990 2 Jan. 1991 5 Jan. 1991 9 Jan. 1991 12 Jan. 1991 15 Jan. 1991 18 Jan. 1991
Replenishment
Concentration of spraywash (%, w/w)
water added (litres)
ethion added (ml)
prereplenishment
postreplenishment
2000 930 345 645 765 965 750 750 720 525
1000 585 293 443 503 503 495 495 480 383
-" 0.04 0.04 0.05 0.06 0.05 0.05 0.05 0.05 0.05
0.05 0.04 0.05 0.05 0.05 0.04 0.04 0.05 0.05 0.05
aTank emptied and refilled. bConcentration of ethion in mud-layer.
0.79 b
132 220
210 200 190 180 170 160
150 140 130
E v
120
-4,
110
z
100 9O 8O 7O 6O
5O 40 30
2O 10 0 JUN
JUL
AUG
SEP
OCT
NOV
DEC
MONTH
1
JAN
FEB
,^^^^,
MAR
APR
MAY
JUN
Fig. 1. Monthly rainfall distribution at Sokoine University of Agriculture, June 1990 to June 1991.
Ticks and tick-borne diseases (TBD) Until the start of the trial, toxaphene (an OC) was used in the spray-race. On the first day of the trial, all animals were examined and found to be moderately infested with ticks (0 5 ticks per animal); most of these ticks were Rhipicephalus spp. or Boophilus decoloratus. After spraying twice with ethion all the ticks were eliminated. Regular examination of the animals after every spraying showed that ticks reappeared on the animals on the 2nd or 3rd day after spraying. The T B D observed during the trial were: 2 cases of East Coast fever (July 1990) and four cases of anaplasmosis distributed as follows: 2 cases in August 1990, one case in November 1990 and one case in December 1990. From January 1991 to June 1991 no case of T B D was observed.
Discussion The fact that none of the animals during the trial showed any signs of toxicity was not unexpected, because the dose of 0.05% used was smaller by far than the maximum non-toxic dermal dose of 0.25% (w/w) recorded for ethion on cattle (Osweiler et al., 1985). The manifestation of toxicity has been observed in goats when a dermal dose of 100 mg/kg was applied (Mosha et al., 1990). The 100 mg/kg dose was about double the 0.25% dermal dose assuming that about 1 litre of the 0.25% dipwash is enough for a 50 kg goat. The trial shows that ethion EC at the concentration of 0.04 0.05% was effective in controlling the various ticks present in the University farm and hence the tickborne diseases. The few tick-borne diseases recorded may be attributed to inexperience in the use of the acaricide, particularly at the beginning of the trial. Tick-borne
133 diseases would easily occur if the animals did not stay in the spray race long enough to be effectively covered by the acaricide. This is believed to be the cause o f the two early cases o f East Coast fever and anaplasmosis. For the two cases o f anaplasmosis which occurred in N o v e m b e r December, 1990, similar reasons m a y be advanced. Furthermore, as the period was a rather rainy one (Fig. 1) the possibility exists that the acaricide was washed from the animals b o d y by rain immediately after spraying. Washing off o f acaricide from the animal's b o d y by water (rain water or other source o f water) is one o f the possible reasons for early occurrence o f tick-borne diseases despite strict adherence to the dipping regime (Cooper, 1980). The efficacy results obtained agree with those achieved by Mbise 1987 (unpublished results), who in his laboratory and field trials in Arusha - - an area o f a higher altitude than M o r o g o r o in Tanzania - - found ethion a suitable acaricide in the control o f various ticks present in the area, i.e., Rhipicephalus appendiculatus, Rhipicephalus evertsi, Boophilus decoloratus and Amblyomma variegatum. On comparing the efficacy o f ethion and dioxathion, which is another OP, Mbise found that ethion had slightly better efficacy than dioxathion. In view o f this good efficacy, ethion forms a good alternative to dioxathion in controlling ticks in Tanzania, especially where OCs like toxaphene have been withdrawn because o f tick resistance. The results obtained in M o r o g o r o and Arusha, Tanzania agree with those previously obtained in Australia and South America, where ethion has been used against one species o f tick only, i.e., Boophilus microplus (Nunez et al., 1985; Palmer, 1976). The concentrations o f ethion in the sprayrace tank appear to be almost constant. This agrees with the view by N u n e z et al. (1985) that ethion mixtures in dip tanks are quite stable.
Acknowledgements We thank M r Peter Jingu for technical help and Miss Jescar Mkami for typing the manuscript.
References Cheminova (1986) Data Manual -- Ethion Technical. Cooper Company (1980) The control of cattle ticks in East and Central Africa. 4tl~ Edn. Wellcome Eastern Africa Ltd. Kabete, Kenya. Mosha, R.D., Gyrd-Hansen, N. and Nielsen, P. (1990) Fate of ethion in goats after intravenous, oral and dermal administration. Pharmacol. Toxicol. 67, 246 251. Nunez, J.L., M unoz-Cobenas, M.E. and Moltedo, H.L. (1985) Boophilusmicroplus.The Common Cattle Tick, p. 94-152, Springer, Berlin. Osweiler, G.D., Carson, T.L., Buck, W.B. and Van Gelder, G.A. (1985) Clinical and Diagnostic Veterinary Toxicology, 3rd Edn. p. 275 320, Kendall/Hunt, Dubuque. Palmer, W.A. (1976). Management of ethion-chlordimeform mixtures in dipping baths. Department of Agriculture, New South Wales Tech. Bull. 9, 1 11.
