ORCID Profile
0000-0001-7685-9370
Current Organisation
NSW Department of Primary Industries
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Publisher: Wiley
Date: 19-05-2011
DOI: 10.1111/J.1751-0813.2011.00719.X
Abstract: Develop a computer simulation model that uses daily meteorological data and farm management practices to predict populations of Trichostrongylus colubriformis, Haemonchus contortus and Teladorsagia (Ostertagia) circumcincta and the evolution of anthelmintic resistance within a sheep flock. Use the model to explore if increased refugia, provided by leaving some adult sheep untreated, would delay development of anthelmintic resistance without compromising nematode control. Compare model predictions with field observations from a breeding flock in Armidale, NSW. Simulate the impact of leaving 1-10% of adult sheep untreated in erse sheep-grazing systems. Predicted populations of Tr. colubriformis and T. circumcincta were less than those observed in the field, attributed to nutritional stress experienced by the sheep during drought and not accounted for by the model. Observed variation in faecal egg counts explained by the model (R(2) ) for these species was 40-50%. The H. contortus populations and R(2) were both low. Leaving some sheep untreated worked best in situations where animals were already grazing or were moved onto pastures with low populations of infective larvae. In those cases, anthelmintic resistance was delayed and nematode control was maintained when 1-4% of adult stock remained untreated. In general, the model predicted that leaving more than 4% of adults untreated did not sufficiently delay the development of anthelmintic resistance to justify the increased production risk from such a strategy. The choice of a drug rotation strategy had an equal or larger effect on nematode control, and selection for resistance, than leaving 1-10% of adults untreated.
Publisher: Wiley
Date: 18-04-2011
DOI: 10.1111/J.1751-0813.2011.00703.X
Abstract: To compare the risk of different treatment scenarios on selecting for anthelmintic resistance on Australian sheep farms. A computer simulation model predicted populations of Trichostrongylus colubriformis, Haemonchus contortus or Teladorsagia (Ostertagia) circumcincta, and the frequency of anthelmintic resistance genes. Nematode populations and the progression of drug resistance for a variety of treatment options and management practices in sheep-rearing areas of Western Australia (WA), Victoria (VIC) and New South Wales (NSW) were simulated. A scoring system was devised to measure the success of each option in delaying resistance to each anthelmintic and in controlling nematode populations. The best option at all sites was combining the new anthelmintic (monepantel) with a triple mixture of benzimidazole, levamisole and abamectin (COM). The next best option was: in NSW, rotation at each treatment between monepantel, moxidectin and COM in VIC, rotation at each treatment between monepantel and COM and in WA, rotation at each treatment between monepantel (used in winter) and COM or moxidectin (used in summer-autumn). In WA, rapid selection for resistance occurred as a consequence of summer-autumn treatments however, if a small percentage of adult stock were left untreated then this selection could be greatly reduced. Despite purposely assuming relatively high resistance to benzimidazole and levamisole, COM was still effective in controlling worms and delaying resistance. Because of cost constraints, it may not be feasible or profitable for producers to always use the combination of all drugs. However, the second- and third-best options still considerably slowed the development of anthelmintic resistance.
Publisher: Wiley
Date: 06-2003
Publisher: Elsevier BV
Date: 09-2016
DOI: 10.1016/J.VETPAR.2016.08.016
Abstract: Early in 2015, sheep in a summer rainfall area of NSW, Australia, displayed signs of haemonchosis despite treatment with monepantel. A faecal egg count reduction test (FECRT) was performed on yearlings with natural field infections using various anthelmintics. Only a four-way combination drench achieved a reduction in faecal egg count (FEC) greater than 95%. The combination contained abamectin, albendazole, levamisole and closantel. Treatments with a derquantel/abamectin combination, monepantel and moxidectin reduced FECs by 93, 31, and 30% respectively. Sheep treated with abamectin displayed an increase in FEC of 22%. Larval differentiation counts conducted 10days post-treatment showed that 100% of survivors were Haemonchus sp. This result confirms for the first time monepantel resistant Haemonchus in sheep in NSW, and is amongst the first of the Australian cases in sheep not associated with goats. A second FECRT was performed using sheep from the moxidectin and abamectin treatment groups in the first FECRT. In this second FECRT, monepantel treatment reduced FECs by 51% and 29% in the sheep previously treated with moxidectin and abamectin respectively. This suggests monepantel, in combination with moxidectin, may give some control against severely abamectin resistant Haemonchus.
Publisher: CSIRO Publishing
Date: 2003
DOI: 10.1071/EA02229
Abstract: Sheep worm infections increasingly threaten the profitability of the Australian sheep industry as the prevalence and severity of anthelmintic resistance continues to rise. Field experiments have demonstrated that the use of drenches that are of reduced efficacy due to resistance can reduce wool production by 10% and significantly reduce sheep sale value. The major factor in benzimidazole (BZ) and levamisole (LV) resistance, and in part macrocyclic lactone (ML) resistance in Haemonchus contortus, is considered to be the excessive frequency of treatment. In Ostertagia circumcincta, ML resistance appears to be related chiefly to interactions between the environment and the time of treatment, where resistant worms surviving drenches are not significantly diluted by worms acquired after treatment. Resistance to the BZs and LV affects almost all Australian sheep farms, and on most drench efficacy is now below a useful level. ML resistance is common in O. circumcincta in Western Australia, and increasingly prevalent in H. contortus in summer rainfall regions. Closantel resistance is a major threat to H.�contortus control in northern New South Wales and southern Queensland. The organophosphate naphthalophos, especially when used in combination with other compounds, has proved useful although variable in efficacy. It is essential that the sheep industry adopts approaches that minimise reliance on chemical control, such as the breeding of worm resistant sheep, use of specific grazing strategies for worm control and apply flock treatment tactics to minimise further resistance development. New non-chemical technologies under development are also expected to contribute to more sustainable worm control. Nutritional regimens that minimise the impact of worm infections and enhance the immune response require investigation and integration into sustainable control practices.
Publisher: Elsevier BV
Date: 07-2012
Publisher: Wiley
Date: 26-11-2014
DOI: 10.1111/AVJ.12271
Abstract: 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). 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. 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. 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.
Publisher: Elsevier BV
Date: 05-2012
DOI: 10.1016/J.VETPAR.2011.11.045
Abstract: Despite the economic importance of nematodes for sheep enterprises, it is often difficult to convince producers to adopt best practice in worm control. In this paper we discuss key issues in effecting change by communicating worm control messages. The adoption of new strategies is affected by many factors including the relative advantage, complexity, compatibility and the ability to trial the proposed change. The visibility of the problem to be solved and proposed positive outcome are also important. Extension c aigns from the last 30 years, including "WormKill" and "CRACK", are used as ex les, and future opportunities and tools, including the internet, for promoting best practice in sheep worm management are discussed.
Location: Australia
No related grants have been discovered for Stephen Love.