Anthelmintic (dewormer) resistance
Anthelmintic (dewormer) resistance is a major issue in the small ruminant industry and an emerging problem in other segments of animal agriculture. Drug resistance exists when an anthelmintic treatment fails to reduce fecal egg counts by more than 95 percent. It is inevitable. Severe resistance exists when treatment fails to reduce worm egg counts by more than 60 percent. Currently, there is resistance to all of the anthelmintics used to treat small ruminants (in the US). However, the level of resistance varies by geographic region and individual farm.
Articles
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Dewormer resistance on farms in the Mid-Atlantic Area. D.J. O'Brien, Delaware State University. [May 2010].
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Do you know which dewormer(s) are effective on your farm? E. Nelson Escobar, University of Maryland Eastern Shore. [Timely Topic, July 2013]
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More on-farm dewormer resistance testing needed: do an LDA!; Dahlia O'Brien, Virginia State University [Timely Topic, October 2015].
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Potential solutions to highly resistant worms in sheep and goats; Steve Hart, Langston University [Timely Topic, October 2013].
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Test your knowledge of the management practices that affect dewormer resistance. Michelle Arnold, DVM. University of Kentucky [September 2015].
Conference proceedings
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Biology of Anthelmintic Resistance: These Ain't Your Father's Parasites; Dr. Ray Kaplan, Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia; 10th Anniversary Conference of the American Consortium for Small Ruminant Parasite Control, Fort Valley, Georgia [May 2013].
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Determining the Level of Efficacy in Anthelmintics; Dr. Ray Kaplan; W4: What Works With Worms Congress, Pretoria, South Africa [May 2015].
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How and Why Resistance to Worms Develops; Dr. Ray Kaplan; W4: What Works With Worms Congress, Pretoria, South Africa [May 2015].
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Sequential Dosing as a Possible Way of Slowing AR; Dave Midgley; W4: What Works With Worms Congress, Pretoria, South Africa [2015].
Factsheets
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Dewormer resistance on Virginia sheep farms. Dahlia O'Brien, Susan Schoenian, and Niki Whitley [2017]
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Drench Resistance and Sheep Worm Control. By Stephen Love, Veterinarian/State Worm Control Coordinator. New South Wales Government, Australia.
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Managing Dewormer Resistance. Best Management Practices. Dahlia O'Brien. [May 2018].
Podcasts
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Opening a parasitic, drug-resistant can of worms. Dr. Ray Kaplan, University of Georgia. Finding Genius Podcast [2020]
Research
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An inconvenient truth: global warming and anthelmintic resistance; Ray Kaplan and Anand N. Vidyashankar; Veterinary Parasitology [2012].
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Anthelmintic Resistance in Gastrointestinal Nematodes and Associated Management Factors in Intermountain West Sheep Flocks. Sheep & Goat Research Journal (pages 30-37). W. Stewart, D. Scott, S. Howell, R. Kaplan, B. Roeder, and T. Murphy [November 2020].
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Prevalence of anthelmintic resistance on sheep and goat farms in the southeastern United States; S.B. Howell, J.M. Burke, J.E. Miller, T.H. Terrill, E. Valencia, M.J. Williams, L.H. Williamson, A.M. Zajac, and R.M. Kaplan; Scientific Reports: Journal of American Veterinary Medical Association [December 2008].
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Prevalence of anthelmintic resistance on sheep and goat farms in the mid-Atlantic region and comparison of in vivo and in vitro detection methods. E.K.Crook, D.J. O’Brien, S.B. Howell, B.E. Storey, N.C. Whitley, J.M. Burke, and R.M.Kaplan. Small Ruminant Research [September 2016].
Videos
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Antiparasitic resistance in cattle, small ruminants, and horses in the US. FDA [2017]
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How to determine effectiveness of dewormers. Reid Redden. Texas A&M AgriLife [2018]
Last updated 11.03.23. Links verified 11.03.23.