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PRODUCTION ANIMALS
PRODUCTION ANIMALS
Prevalence and severity of anthelmintic resistance in ovine gastrointestinal nematodes in Australia (2009–2012) MC Playford,a AN Smith,a S Love,b RB Besier,c P Kluverd and JN Baileyd*
Objective This study aimed to provide an indication of the prevalence and severity of anthelmintic resistance (AR) in the Australian sheep industry by compiling the results of faecal worm egg count reduction tests (FECRTs). Methods Government and private parasitology laboratories, pharmaceutical companies and veterinarians known to have conducted FECRTs were asked to provide results that conformed to Australian and New Zealand standard diagnostic procedures. Results Data were available from a total of 390 tests, with larval differentiation conducted in 222 cases. Pooled results from all states for the macrocyclic lactone (ML) class showed a lower prevalence of AR against combined species for moxidectin (54%) compared with abamectin (77%) and ivermectin (87%). Analysis by state revealed higher levels of ML-resistant Teladorsagia sp. in Tasmania and Western Australia than in other states and ML-resistant Haemonchus sp. was more frequently detected in New South Wales. Conclusion This compilation of results of FECRTs conducted by Australian parasitology laboratories in 2009–12 showed widespread AR of the common sheep nematodes (Teladorsagia, Trichostrongylus and Haemonchus) to all broad-spectrum anthelmintics, with the exception of monepantel, whether used singly or in combination. Keywords anthelmintic resistance; faecal egg count reduction test; nematode control; sheep Abbreviations AAD, amino-acetonitrile derivative; ABA, abamectin; AR, anthelmintic resistance; BZ, benzimidazole; CLOS, closantel; epg, eggs per gram of faeces; FECRT, faecal egg count reduction test; IVM, ivermectin; LEV, levamisole; ML, macrocyclic lactone; MOX, moxidectin; MPL, monepantel; NAP, naphthalophos; OP, organophosphate (pyraclofos and naphthalophos); PYR, pyraclofos
A combination of anthelmintic use, pasture management and sheep breeding has traditionally been used in Australia to ensure acceptable parasite control and new information about parasite biology has led to a greater range of integrated parasite management techniques.6,7 The broad-spectrum drench classes used in Australia include benzimidazole (BZ),8 levamisole (LEV), macrocyclic lactones (ML) and amino-acetonitrile derivatives (AAD), and combinations of two or more of these anthelmintic classes.9,10 Because of overreliance on anthelmintics and the use of unsustainable control programs, anthelmintic resistance (AR) has become a major problem on many Australian sheep farms and, in many cases, by 2003 just one drench group remained effective against at least one major species of worm.1 Coles et al. state that ‘anthelmintic resistance is present when there is a greater frequency of individuals within a population able to tolerate doses of a compound than in a normal population of the same species and is heritable’.10 For diagnostic purposes in Australia, AR is said to exist if the reduction in the arithmetic mean from the drench group is less than 95% (compared with untreated sheep at days 10–14 or the treated group prior to treatment) and the lower 95% confidence limit is less than the 90% reduction level.11
N
The first case of AR to the BZ class in Australia was identified in 1966, just 5 years after the anthelmintic agent was released,12 and by 2011, BZ resistance was detected on approximately 90% of tested properties across Australia.13 Teladorsagia circumcincta, Trichostrongylus colubriformis and Haemonchus contortus have now shown resistance,1,14 though differing in prevalence and severity among species, to all of the widely used broad-spectrum anthelmintic classes,13 with the exception of the recently released AAD class.15
*Corresponding author. a Dawbuts Pty Ltd, Camden, NSW, Australia b NSW Department of Primary Industries, UNE Armidale, NSW, Australia c Department of Agriculture and Food Western Australia, Albany, WA, Australia d Novartis Animal Health Australasia Pty Ltd, Locked Bag 2003, North Ryde, New South Wales 1670, Australia; [email protected]
The aims of the present study were to provide an estimate of the current prevalence of AR in sheep nematodes across Australia through the collation of results from recently conducted drench tests (i.e. FECRTs) and to provide an indication of the severity of AR according to species of nematode and class of anthelmintic. These results would also provide the basis for comparing AR in the present study with previous reports from Australia.16,17
Aust Vet J 2014;92:464–471
doi: 10.1111/avj.12271
ematode parasites are a constant threat to the health, welfare and productivity of sheep on Australian farms, because the temperate climate and pasturelands favour their development and survival.1 In particular, parasites of the genera
464
Trichostrongylus (black scour worm), Teladorsagia (brown stomach worm) and Haemonchus (barber’s pole worm) can cause anaemia, diarrhoea and reductions in body weight gain, reproductive rates and wool growth.2 Affected sheep are predisposed to breech soiling (i.e. dag formation) and flystrike.3,4 The combined cost of production loss and control measures associated with internal parasites to Australian sheep producers has been estimated to be A$369 million per year.5
Australian Veterinary Journal Volume 92, No 12, December 2014
© 2014 Australian Veterinary Association
Material and methods Survey In total, 43 laboratories and veterinary services listed as having a parasitology service7 were initially approached by email, with follow-up phone calls made to non-responders; 7 veterinary pharmaceutical companies known to conduct FECRTs were also contacted, but only 2 agreed to supply data. Many of the laboratories and veterinary clinics approached either did not conduct any FECRTs or their methods were not consistent with the study guidelines. To be included in the study, the case submissions had to meet eligibility criteria consistent with the World Association for the Advancement of Veterinary Parasitology and Australian and New Zealand Standard Diagnostic Procedures, Sub-Committee on Animal Health Laboratory Standards guidelines:11,18 (1) ≥10 samples per treatment group; (2) concurrent untreated control group; (3) faecal culture conducted on each treatment group for differentiation of nematode larvae; and (4) each worm genus present at >100 eggs per gram (epg). Only the results of FECRTs conducted between 1 January 2009 and 30 March 2012 were analysed to provide an up-to-date overview of the prevalence of AR. The FECRT is the most commonly used method of identifying the efficacy of anthelmintics against gastrointestinal nematodes in commercial sheep flocks.19 The test compares the FECs from sheep treated with anthelmintic(s) with those of sheep with no anthelmintic treatment (control), to evaluate the reduction in the FEC as a result of the anthelmintic.19 Data were anonymised, but region (designated by town or postcode) was provided. Laboratory methods The worm FECRT is a standard on-farm test conducted by treating groups of sheep with anthelmintics and then collecting faeces from them for an egg count 10–14 days later. The FECs are compared with those of an untreated control group and the percentage reduction attributable to each anthelmintic is calculated. Culture of the faeces to allow eggs to hatch is then conducted in order to identify the genera or species of nematodes present. This is possible at or after the third larval stage, usually harvested after 7 days of incubation. Larvae are recovered from the culture medium, stained with iodine, measured and their physical characteristics noted. Using a key, the genera of nematodes and their proportions in the faeces can be determined.11 Parasitological examinations were conducted as described for Australian and New Zealand Standard Diagnostic Procedures.11 Fresh faecal samples were weighed and mixed with saturated saline. Nematode eggs were counted using a McMaster chamber (JA Whitlock & Co., NSW, Aust). All worm genera were identified from larval cultures by visual differentiation of third-stage larvae to genus level using a key based on larval measurements and morphology. The genus composition of a culture was determined by examining 100 randomly selected larvae. The treatment group’s average FEC was compared with that of the control group, and from this, the FEC reduction (FECR) by each anthelmintic treatment for each genus was calculated for each sub-
© 2014 Australian Veterinary Association
mission case. A FECR ≥95% was taken to indicate anthelmintic susceptibility, with AR being defined as a FECR
PRODUCTION ANIMALS
PRODUCTION ANIMALS
Prevalence and severity of anthelmintic resistance in ovine gastrointestinal nematodes in Australia (2009–2012) MC Playford,a AN Smith,a S Love,b RB Besier,c P Kluverd and JN Baileyd*
Objective This study aimed to provide an indication of the prevalence and severity of anthelmintic resistance (AR) in the Australian sheep industry by compiling the results of faecal worm egg count reduction tests (FECRTs). Methods Government and private parasitology laboratories, pharmaceutical companies and veterinarians known to have conducted FECRTs were asked to provide results that conformed to Australian and New Zealand standard diagnostic procedures. Results Data were available from a total of 390 tests, with larval differentiation conducted in 222 cases. Pooled results from all states for the macrocyclic lactone (ML) class showed a lower prevalence of AR against combined species for moxidectin (54%) compared with abamectin (77%) and ivermectin (87%). Analysis by state revealed higher levels of ML-resistant Teladorsagia sp. in Tasmania and Western Australia than in other states and ML-resistant Haemonchus sp. was more frequently detected in New South Wales. Conclusion This compilation of results of FECRTs conducted by Australian parasitology laboratories in 2009–12 showed widespread AR of the common sheep nematodes (Teladorsagia, Trichostrongylus and Haemonchus) to all broad-spectrum anthelmintics, with the exception of monepantel, whether used singly or in combination. Keywords anthelmintic resistance; faecal egg count reduction test; nematode control; sheep Abbreviations AAD, amino-acetonitrile derivative; ABA, abamectin; AR, anthelmintic resistance; BZ, benzimidazole; CLOS, closantel; epg, eggs per gram of faeces; FECRT, faecal egg count reduction test; IVM, ivermectin; LEV, levamisole; ML, macrocyclic lactone; MOX, moxidectin; MPL, monepantel; NAP, naphthalophos; OP, organophosphate (pyraclofos and naphthalophos); PYR, pyraclofos
A combination of anthelmintic use, pasture management and sheep breeding has traditionally been used in Australia to ensure acceptable parasite control and new information about parasite biology has led to a greater range of integrated parasite management techniques.6,7 The broad-spectrum drench classes used in Australia include benzimidazole (BZ),8 levamisole (LEV), macrocyclic lactones (ML) and amino-acetonitrile derivatives (AAD), and combinations of two or more of these anthelmintic classes.9,10 Because of overreliance on anthelmintics and the use of unsustainable control programs, anthelmintic resistance (AR) has become a major problem on many Australian sheep farms and, in many cases, by 2003 just one drench group remained effective against at least one major species of worm.1 Coles et al. state that ‘anthelmintic resistance is present when there is a greater frequency of individuals within a population able to tolerate doses of a compound than in a normal population of the same species and is heritable’.10 For diagnostic purposes in Australia, AR is said to exist if the reduction in the arithmetic mean from the drench group is less than 95% (compared with untreated sheep at days 10–14 or the treated group prior to treatment) and the lower 95% confidence limit is less than the 90% reduction level.11
N
The first case of AR to the BZ class in Australia was identified in 1966, just 5 years after the anthelmintic agent was released,12 and by 2011, BZ resistance was detected on approximately 90% of tested properties across Australia.13 Teladorsagia circumcincta, Trichostrongylus colubriformis and Haemonchus contortus have now shown resistance,1,14 though differing in prevalence and severity among species, to all of the widely used broad-spectrum anthelmintic classes,13 with the exception of the recently released AAD class.15
*Corresponding author. a Dawbuts Pty Ltd, Camden, NSW, Australia b NSW Department of Primary Industries, UNE Armidale, NSW, Australia c Department of Agriculture and Food Western Australia, Albany, WA, Australia d Novartis Animal Health Australasia Pty Ltd, Locked Bag 2003, North Ryde, New South Wales 1670, Australia; [email protected]
The aims of the present study were to provide an estimate of the current prevalence of AR in sheep nematodes across Australia through the collation of results from recently conducted drench tests (i.e. FECRTs) and to provide an indication of the severity of AR according to species of nematode and class of anthelmintic. These results would also provide the basis for comparing AR in the present study with previous reports from Australia.16,17
Aust Vet J 2014;92:464–471
doi: 10.1111/avj.12271
ematode parasites are a constant threat to the health, welfare and productivity of sheep on Australian farms, because the temperate climate and pasturelands favour their development and survival.1 In particular, parasites of the genera
464
Trichostrongylus (black scour worm), Teladorsagia (brown stomach worm) and Haemonchus (barber’s pole worm) can cause anaemia, diarrhoea and reductions in body weight gain, reproductive rates and wool growth.2 Affected sheep are predisposed to breech soiling (i.e. dag formation) and flystrike.3,4 The combined cost of production loss and control measures associated with internal parasites to Australian sheep producers has been estimated to be A$369 million per year.5
Australian Veterinary Journal Volume 92, No 12, December 2014
© 2014 Australian Veterinary Association
Material and methods Survey In total, 43 laboratories and veterinary services listed as having a parasitology service7 were initially approached by email, with follow-up phone calls made to non-responders; 7 veterinary pharmaceutical companies known to conduct FECRTs were also contacted, but only 2 agreed to supply data. Many of the laboratories and veterinary clinics approached either did not conduct any FECRTs or their methods were not consistent with the study guidelines. To be included in the study, the case submissions had to meet eligibility criteria consistent with the World Association for the Advancement of Veterinary Parasitology and Australian and New Zealand Standard Diagnostic Procedures, Sub-Committee on Animal Health Laboratory Standards guidelines:11,18 (1) ≥10 samples per treatment group; (2) concurrent untreated control group; (3) faecal culture conducted on each treatment group for differentiation of nematode larvae; and (4) each worm genus present at >100 eggs per gram (epg). Only the results of FECRTs conducted between 1 January 2009 and 30 March 2012 were analysed to provide an up-to-date overview of the prevalence of AR. The FECRT is the most commonly used method of identifying the efficacy of anthelmintics against gastrointestinal nematodes in commercial sheep flocks.19 The test compares the FECs from sheep treated with anthelmintic(s) with those of sheep with no anthelmintic treatment (control), to evaluate the reduction in the FEC as a result of the anthelmintic.19 Data were anonymised, but region (designated by town or postcode) was provided. Laboratory methods The worm FECRT is a standard on-farm test conducted by treating groups of sheep with anthelmintics and then collecting faeces from them for an egg count 10–14 days later. The FECs are compared with those of an untreated control group and the percentage reduction attributable to each anthelmintic is calculated. Culture of the faeces to allow eggs to hatch is then conducted in order to identify the genera or species of nematodes present. This is possible at or after the third larval stage, usually harvested after 7 days of incubation. Larvae are recovered from the culture medium, stained with iodine, measured and their physical characteristics noted. Using a key, the genera of nematodes and their proportions in the faeces can be determined.11 Parasitological examinations were conducted as described for Australian and New Zealand Standard Diagnostic Procedures.11 Fresh faecal samples were weighed and mixed with saturated saline. Nematode eggs were counted using a McMaster chamber (JA Whitlock & Co., NSW, Aust). All worm genera were identified from larval cultures by visual differentiation of third-stage larvae to genus level using a key based on larval measurements and morphology. The genus composition of a culture was determined by examining 100 randomly selected larvae. The treatment group’s average FEC was compared with that of the control group, and from this, the FEC reduction (FECR) by each anthelmintic treatment for each genus was calculated for each sub-
© 2014 Australian Veterinary Association
mission case. A FECR ≥95% was taken to indicate anthelmintic susceptibility, with AR being defined as a FECR
