LETTERS TO THE EDITOR EFFICIENCY O F RAFOXANIDE AND NAPHTHALOPHOS AGAINST INHIBITED HA EMONCH US CON TORTUS The increase in resistance to benzimidazole anthelmintics by
Haemonchus contortus in New South Wales has led to promotion of drenching schemes designed to either retard development of resistance or circumvent it once it has appeared. One program in the latter category proposes the use of a narrow spectrum anthelmintic to control benzimidazole resistant H . contortus used alternately with a benzimidazole to control remaining species (Prichard 1978). As narrow spectrum drenches are usually less expensive this scheme will reduce costs of drenching during summer when H . contortus is the predominant species. Two narrow spectrum anthelmintics frequently used in rotation with a broad spectrum anthelmintic are rafoxanidel and naphthalophost. Rafoxanide has been found to be effective against adult benzimidazole resistant H . contortus (Campbell and Hotson 1971) and although it is effective against normally developing fourth stage larvae at 8 days post infection (Egerton et al 1970) it is ineffective against inhibited non-benzimidazole resistant H . contortus larvae (Snijders et a1 1973). Naphthalophos is effective against adult benzimidazole resistant strains of H . contortus (Campbell et a1 1978). However there have been no studies of the efficiencies of these two narrow spectrum anthelmintics against inhibited larvae of benzimidazole resistant H . contortus. The present study was undertaken to determine the efficiency of 2 narrow spectrum anthelmintics, rafoxanide and naphthalophos, against adult and inhibited benzimidazole resistant H . contortus. Thirty-six weaner lambs were given a 14 mg/kg dose of levamisole$ based on their average body weight and allowed to Ranide, Merck, Sharp and Dohme (Australia) Ply Ltd, Granville, New South Wales t Rametin H,Bayer Australia Ply Ltd, Botany. New South Wales $ Ripercol, Cooper Australia Ltd, Concord, New South Wales
graze paddocks infested with benzimidazole resistant H . contortus. This population of H . conforms was described previously as having had an LD,, of 159 mg/kg of thiabendazoles (Le Jambre et a1 1976). After grazing for 28 days, the lambs were housed for 21 days under conditions which precluded further infection. The lambs were ranked in order of their faecal egg counts and the highest 12 randomly assigned to one of 12 sub-groups. This process was repeated until all sub-groups were assigned 3 animals. Six sub-groups were randomly allocated to a rafoxanide treatment group and 6 to a naphthalophos treatment group. Both anthelmintics were given by intra ruminal injection. The dose levels of anthelmintics based on bodyweight were: rafoxanide nil, 3.0,4.5,7.5, 10.0 and 15 mg/kg naphthalophos nil, 6.25, 9.38, 12.50, 18.75 and 25.00 mg/kg. All were killed 3 days after anthelmintic treatment and their abomasa removed immediately and the contents washed and scraped into 2 1 graduated cylinders. After settling, the supernatant was removed and the remaining 500 to 600 ml preserved with formalin. Random samples were taken of the preserved material and the worms counted. Numbers of adult H . contortus were estimated from a random sample of 1/10 total volume, while the number of fourth stage larvae were estimated from 1/10 total volume. The abomasa were digested in 1.7% HCI at 38°C for 4 h and the number of adult and larval H . contortus in the digest were estimated from a 1/10 sample. Rafoxanide was very efficient against adult H . contortus with no adult worms surviving the recommended dose rate of
5 Thibenzole. Merck, Sharp and Dohme (Australia) Pty Lid, Granville, New South Wales
TABLE I
Comparison of the Anthelmintic Efficiency of Rafoxanide and Naph thalophos Against Benzimidazole Resistant Adults and Inhibited Larvae of H. contortus Rafoxanide Dose m g h
0 3 .O 4.5 7.5 10.0 15.0 F statistic Level of significance
Naphthalophos
Geometric Mean Adults
Inhibited Larvae
692a 162;’ 51 OC OC 3c
3020 1698 708 3890 219 3548
10.12
0.001
1.71 N.S.
Dose w/kg
Geometric Mean Adults
0 6.25 9.38 12.50 18.75 25.00
776d 14Sd Oe Oe 2e 2e 10.29 0.001
Inhibited Larvae 812$ 223Sf 27g 4gh 4gh Oh 12.16
0.001
Means in the same column with the same superscript are not significantly different when tested by Duncan’s multiple-range test.
346
Australian Veterinary Journal, Vol. 5 5 , July, 1979
7.5 mg/kg. However againsi inhibited H . contortus larvae there was no significant effect of treatment even at twice the recommended dose rate (Table 1). Naphthalophos significantly reduced both adults and inhibited larvae at 9.38 mg/kg or 2/3 the recommended dose rate (Table 1). On the Northern Tablelands of New South Wales haemonchosis is primarily a disease of lambs in their first summer or autumn (Anderson et a1 1978). It has been shown that eggs deposited in spring by previously inhibited H . contorfus in older sheep can be an important source of infection for young sheep that subsequently graze the same pasture (Barger and Le Jambre, personal communication). It is advisable therefore to drench sheep in late winter with an anthelmintic that is effective against inhibited larvae. The present experiment indicates that of the 2 narrow spectrum anthelmintics tested, only naphthalophos is an effective winter drench. Rafoxanide would be best used as a flukicide or if used to control benzimidazole resistant H . contortus it should only be used in the summer months when inhibited larvae are less prevalent.
L.F. LE JAMBRE, I.A. BARGER.
CSIRO, Division of Animal Health, Pastoral Research Laboratory, Armidale, New South Wales 2350
5 March 1979 References Anderson, N., Dash, K.M., Donald, A.D., Southcott, W.H. and Waller, P.J. (1978) - TheEpidemiologyandConfrolof Gastrointestinal Parasites of Sheep in Austrafia. Ed A.D. Donald, W.H. Southcott and J.K. Dineen. CSIRO, Melbourne, p24. Campbell, N.J. and Hotson, I.K. (1971) - Ausl. vet. J. 47: 5. Campbell, N.J., Hall, C.A., Kelly. . J.D. and Martin, I.C.A. (1978) - Aust. vet. J. 54: 23. Egerton, J.R., Yakstis, J.J. and Campbell, W.C. (1970) Res. Vef. Sci. 11: 382. Le Jambre, L.F., Southcott, W.H. and Dash, K.M. (1976) Int. 1.Parasit. 6: 217. Prichard, R.K. (1978) - The Epidemiology and Control of Gastrointestinal Parasites o f Sheep in Australia. Eds. A.D. Donald, W.H. Southcott and J.K. Dineen, CSIRO, Melbourne, p.76. Snijders, A.J., Horak, I.G. and Louw, J.P. (1973) - J. S. Afr. vet. Ass. 44: 25 1.
RESISTANCE OF HAEMONCHUS CONTORTUSTO OXFENDAZOLE Oxfendazole was reported by Averkin et a1 (1975) to be a highly effective anthelmintic against experimental and natural nematode infections in laboratory and domestic animals. Kistner et a1 (1972-1976) demonstrated that the dose level of 5 mg/kg bodyweight removed greater than 90% of natural infections of Haemoncbus confortus in sheep. More recently, oxfendazole was shown to be 100% effective against a laboratory strain (Kistner and Wyse 1978) and field populations (Webb et af 1979a) of H. contortus resistant to other benzimidazole anthelmintics. Following its commercial release in Australia at the end of 1977, oxfendazole has been used widely as a broad spectrum anthelmintic for sheep and cattle. This letter reports evidence of a natural infection of H . contortus in sheep which was resistant to treatment with oxfendazole. A lack of clinical response in a group of naturally parasitised sheep following treatment with oxfendazole was reported to us from a commercial property on the northern tablelands of New South Wales. In an initial investigation, faecal samples were collected from 20 sheep which were then treated with oxfendazole* at the manufacturer’s recommended dose rate of 4.65 mg/kg. Four days later faecal samples were collected from the same sheep. The mean strongyle ova per gram (opg) count for the group before treatment was 2,725 (range 0-11,200) and after treatment was 2,458 (range 200-10,600). Bulk faecal cultures prepared from the group showed that 97% of the ova in the first sampling and 100% in the second were H. contortus. A second trial was undertaken immediately on the property using 10 different sheep which were individually identified and weighed. Faecal samples were collected from each sheep and the latter were assigned to 1 of 2 groups of 5 according to the strongyle ova counts. Sheep in Group 1 were treated with OXfendazole at a dose rate of 4.65 mg/kg according to individual
*Systameu, Cooper AUStralta Lfd, Concord, New South Wales.
Australian VeterinaryJournal, Vol. 55, July, 1979
bodyweight while sheep in Group 2 were left untreated as controls. Four days later all 10 sheep were slaughtered. Strongyle opg counts in faecal samples collected immediately before and after treatment together with total worm counts of all sheep are shown in Table 1. All larvae obtained from individual faecal cultures were H. contortus. Oxfendazole removed 47.8% adult and 48.4% immature H . contortus worms in the treated group when compared with the untreated controls. Four days after treatment, oxfendazole had reduced the output of H . contortus ova in the treated group by 43.4%. Compared with the reported efficiency of oxfendazole (Averkin 1975; Kistner and Wyse 1978; Webb et a1 1979a) this result indicates that individuals within H. contortus populations in sheep on this property are resistant to this anthelmintic. This contrasts with our previous communication (Webb et a1 1979a) in which no evidence of resistance to oxfendazole was found in 4 populations with varying resistance to other benzimidazole anthelmintics. This highlights the sporadic nature of the occurrence of resistance o f H . confortus to members o f the benzimidazole group of anthelmintics in an area where benzimidazole resistance is known to be widespread (Webb et a1 1979b). It further confirms the contention of Le Jambre e t a1 (1979) that members of the benzimidazole group of anthelmintics cannot be relied upon to control outbreaks of clinical naemonchosis in sheep in such areas. We thank Wellcome Australia Ltd for referring this case to us and for the purchase of experimental sheep.
R. F. WEBB, C. H. McCULLY, New South Wales DeDartment of Agriculture, Regional Veterinary Laboratory, Private Mailbag, Armidale, New South Wales, 2350. 7May, 1979 347
Haemonchus contortus in New South Wales has led to promotion of drenching schemes designed to either retard development of resistance or circumvent it once it has appeared. One program in the latter category proposes the use of a narrow spectrum anthelmintic to control benzimidazole resistant H . contortus used alternately with a benzimidazole to control remaining species (Prichard 1978). As narrow spectrum drenches are usually less expensive this scheme will reduce costs of drenching during summer when H . contortus is the predominant species. Two narrow spectrum anthelmintics frequently used in rotation with a broad spectrum anthelmintic are rafoxanidel and naphthalophost. Rafoxanide has been found to be effective against adult benzimidazole resistant H . contortus (Campbell and Hotson 1971) and although it is effective against normally developing fourth stage larvae at 8 days post infection (Egerton et al 1970) it is ineffective against inhibited non-benzimidazole resistant H . contortus larvae (Snijders et a1 1973). Naphthalophos is effective against adult benzimidazole resistant strains of H . contortus (Campbell et a1 1978). However there have been no studies of the efficiencies of these two narrow spectrum anthelmintics against inhibited larvae of benzimidazole resistant H . contortus. The present study was undertaken to determine the efficiency of 2 narrow spectrum anthelmintics, rafoxanide and naphthalophos, against adult and inhibited benzimidazole resistant H . contortus. Thirty-six weaner lambs were given a 14 mg/kg dose of levamisole$ based on their average body weight and allowed to Ranide, Merck, Sharp and Dohme (Australia) Ply Ltd, Granville, New South Wales t Rametin H,Bayer Australia Ply Ltd, Botany. New South Wales $ Ripercol, Cooper Australia Ltd, Concord, New South Wales
graze paddocks infested with benzimidazole resistant H . contortus. This population of H . conforms was described previously as having had an LD,, of 159 mg/kg of thiabendazoles (Le Jambre et a1 1976). After grazing for 28 days, the lambs were housed for 21 days under conditions which precluded further infection. The lambs were ranked in order of their faecal egg counts and the highest 12 randomly assigned to one of 12 sub-groups. This process was repeated until all sub-groups were assigned 3 animals. Six sub-groups were randomly allocated to a rafoxanide treatment group and 6 to a naphthalophos treatment group. Both anthelmintics were given by intra ruminal injection. The dose levels of anthelmintics based on bodyweight were: rafoxanide nil, 3.0,4.5,7.5, 10.0 and 15 mg/kg naphthalophos nil, 6.25, 9.38, 12.50, 18.75 and 25.00 mg/kg. All were killed 3 days after anthelmintic treatment and their abomasa removed immediately and the contents washed and scraped into 2 1 graduated cylinders. After settling, the supernatant was removed and the remaining 500 to 600 ml preserved with formalin. Random samples were taken of the preserved material and the worms counted. Numbers of adult H . contortus were estimated from a random sample of 1/10 total volume, while the number of fourth stage larvae were estimated from 1/10 total volume. The abomasa were digested in 1.7% HCI at 38°C for 4 h and the number of adult and larval H . contortus in the digest were estimated from a 1/10 sample. Rafoxanide was very efficient against adult H . contortus with no adult worms surviving the recommended dose rate of
5 Thibenzole. Merck, Sharp and Dohme (Australia) Pty Lid, Granville, New South Wales
TABLE I
Comparison of the Anthelmintic Efficiency of Rafoxanide and Naph thalophos Against Benzimidazole Resistant Adults and Inhibited Larvae of H. contortus Rafoxanide Dose m g h
0 3 .O 4.5 7.5 10.0 15.0 F statistic Level of significance
Naphthalophos
Geometric Mean Adults
Inhibited Larvae
692a 162;’ 51 OC OC 3c
3020 1698 708 3890 219 3548
10.12
0.001
1.71 N.S.
Dose w/kg
Geometric Mean Adults
0 6.25 9.38 12.50 18.75 25.00
776d 14Sd Oe Oe 2e 2e 10.29 0.001
Inhibited Larvae 812$ 223Sf 27g 4gh 4gh Oh 12.16
0.001
Means in the same column with the same superscript are not significantly different when tested by Duncan’s multiple-range test.
346
Australian Veterinary Journal, Vol. 5 5 , July, 1979
7.5 mg/kg. However againsi inhibited H . contortus larvae there was no significant effect of treatment even at twice the recommended dose rate (Table 1). Naphthalophos significantly reduced both adults and inhibited larvae at 9.38 mg/kg or 2/3 the recommended dose rate (Table 1). On the Northern Tablelands of New South Wales haemonchosis is primarily a disease of lambs in their first summer or autumn (Anderson et a1 1978). It has been shown that eggs deposited in spring by previously inhibited H . contorfus in older sheep can be an important source of infection for young sheep that subsequently graze the same pasture (Barger and Le Jambre, personal communication). It is advisable therefore to drench sheep in late winter with an anthelmintic that is effective against inhibited larvae. The present experiment indicates that of the 2 narrow spectrum anthelmintics tested, only naphthalophos is an effective winter drench. Rafoxanide would be best used as a flukicide or if used to control benzimidazole resistant H . contortus it should only be used in the summer months when inhibited larvae are less prevalent.
L.F. LE JAMBRE, I.A. BARGER.
CSIRO, Division of Animal Health, Pastoral Research Laboratory, Armidale, New South Wales 2350
5 March 1979 References Anderson, N., Dash, K.M., Donald, A.D., Southcott, W.H. and Waller, P.J. (1978) - TheEpidemiologyandConfrolof Gastrointestinal Parasites of Sheep in Austrafia. Ed A.D. Donald, W.H. Southcott and J.K. Dineen. CSIRO, Melbourne, p24. Campbell, N.J. and Hotson, I.K. (1971) - Ausl. vet. J. 47: 5. Campbell, N.J., Hall, C.A., Kelly. . J.D. and Martin, I.C.A. (1978) - Aust. vet. J. 54: 23. Egerton, J.R., Yakstis, J.J. and Campbell, W.C. (1970) Res. Vef. Sci. 11: 382. Le Jambre, L.F., Southcott, W.H. and Dash, K.M. (1976) Int. 1.Parasit. 6: 217. Prichard, R.K. (1978) - The Epidemiology and Control of Gastrointestinal Parasites o f Sheep in Australia. Eds. A.D. Donald, W.H. Southcott and J.K. Dineen, CSIRO, Melbourne, p.76. Snijders, A.J., Horak, I.G. and Louw, J.P. (1973) - J. S. Afr. vet. Ass. 44: 25 1.
RESISTANCE OF HAEMONCHUS CONTORTUSTO OXFENDAZOLE Oxfendazole was reported by Averkin et a1 (1975) to be a highly effective anthelmintic against experimental and natural nematode infections in laboratory and domestic animals. Kistner et a1 (1972-1976) demonstrated that the dose level of 5 mg/kg bodyweight removed greater than 90% of natural infections of Haemoncbus confortus in sheep. More recently, oxfendazole was shown to be 100% effective against a laboratory strain (Kistner and Wyse 1978) and field populations (Webb et af 1979a) of H. contortus resistant to other benzimidazole anthelmintics. Following its commercial release in Australia at the end of 1977, oxfendazole has been used widely as a broad spectrum anthelmintic for sheep and cattle. This letter reports evidence of a natural infection of H . contortus in sheep which was resistant to treatment with oxfendazole. A lack of clinical response in a group of naturally parasitised sheep following treatment with oxfendazole was reported to us from a commercial property on the northern tablelands of New South Wales. In an initial investigation, faecal samples were collected from 20 sheep which were then treated with oxfendazole* at the manufacturer’s recommended dose rate of 4.65 mg/kg. Four days later faecal samples were collected from the same sheep. The mean strongyle ova per gram (opg) count for the group before treatment was 2,725 (range 0-11,200) and after treatment was 2,458 (range 200-10,600). Bulk faecal cultures prepared from the group showed that 97% of the ova in the first sampling and 100% in the second were H. contortus. A second trial was undertaken immediately on the property using 10 different sheep which were individually identified and weighed. Faecal samples were collected from each sheep and the latter were assigned to 1 of 2 groups of 5 according to the strongyle ova counts. Sheep in Group 1 were treated with OXfendazole at a dose rate of 4.65 mg/kg according to individual
*Systameu, Cooper AUStralta Lfd, Concord, New South Wales.
Australian VeterinaryJournal, Vol. 55, July, 1979
bodyweight while sheep in Group 2 were left untreated as controls. Four days later all 10 sheep were slaughtered. Strongyle opg counts in faecal samples collected immediately before and after treatment together with total worm counts of all sheep are shown in Table 1. All larvae obtained from individual faecal cultures were H. contortus. Oxfendazole removed 47.8% adult and 48.4% immature H . contortus worms in the treated group when compared with the untreated controls. Four days after treatment, oxfendazole had reduced the output of H . contortus ova in the treated group by 43.4%. Compared with the reported efficiency of oxfendazole (Averkin 1975; Kistner and Wyse 1978; Webb et a1 1979a) this result indicates that individuals within H. contortus populations in sheep on this property are resistant to this anthelmintic. This contrasts with our previous communication (Webb et a1 1979a) in which no evidence of resistance to oxfendazole was found in 4 populations with varying resistance to other benzimidazole anthelmintics. This highlights the sporadic nature of the occurrence of resistance o f H . confortus to members o f the benzimidazole group of anthelmintics in an area where benzimidazole resistance is known to be widespread (Webb et a1 1979b). It further confirms the contention of Le Jambre e t a1 (1979) that members of the benzimidazole group of anthelmintics cannot be relied upon to control outbreaks of clinical naemonchosis in sheep in such areas. We thank Wellcome Australia Ltd for referring this case to us and for the purchase of experimental sheep.
R. F. WEBB, C. H. McCULLY, New South Wales DeDartment of Agriculture, Regional Veterinary Laboratory, Private Mailbag, Armidale, New South Wales, 2350. 7May, 1979 347
