Internal Parasites, Part II - Control

1. Internal Parasites, Part II - Control INAG 120 – Equine Health Management November 16, 2011

2. Deworming Protocols • Rotational Purge Deworming: • Goal is to keep the load of eggs and larvae to a minimum • Done every 8-12 weeks via oral paste • Kills adult and/or larval stages of worms inside the horse before they start producing eggs

3. Drawbacks of Purge Deworming • If other horses in same area not dewormed when needed, environmental reduction won’t work • Some parasite eggs can live as long as 30 years in the soil! • Immature worms  mature worms = migration through intestinesand other tissues = damage! • Success depends on timing • Many purge dewormers don’t kill bots

4. Myths: Vets must tube-worm for it to be effective • Only way to guarantee that all the drug is given • Old dewormers were irritating or bad-tasting

5. Myth: Toxicity will build over time in my horse • Organophosphates (used in 60’s and 70’s) did cause problems • Major concern with modern dewormers: • Ascarid impaction in foals

6. Myth: Dewormers aren’t safe for use in broodmares • If drug label says it’s safe for mares: • Manufacturer must TEST it for FDA approval • Requires 2 years of demonstrated efficacy • The Pfizer Babies of CSU • Praziquantel studyin France • Quest?

7. Myth: Diatomaceous Earth is just as effective as chemical dewormers • Herbs and other compounds are not required to be tested (not FDA-certified) • No scientific evidence supports use as dewormer

8. Myth: Rotational deworming will prevent development of resistance • Rotational deworming started about 40 years ago • Reason was NOT resistance • Earlier dewormers were not broad-spectrum

9. Purge Deworming Drugs • How they work • Classes & Brand Names • Benzimidazoles (Panacur Pack) • Tetrahydropyrimidines (PyrantelPamoate) • Heterocyclic compounds (Piperazine) • Macrocycliclactones (Ivermectin/Moxidectin) • Isoquinoline-Pyrozines (Praziquantel) • Safety and efficacy

10. Dewormer Products • All must be approved by FDA • Rigorous testing required • Must be proven safe and effective • Must remove at least 90% of target parasites • Most are broad-spectrum • Don’t require refrigeration but can be damaged by excessive heat

11. How do they work? • Nematocides • Death by starvation • Death by paralysis • Worms can’t store energy • Must eat continuously • Most parasites will die within 24 hours if eating process is interrupted • Paralysis blocks ability to stay in gut

12. Benzimidazoles • Interfere with metabolism on a cellular level • Bind to a particular structure, thereby blocking energy metabolism • Because of mechanism of action, can also kill eggs • Available in granules, paste and suspension • More effective when given several days in a row

13. Panacur Powerpac • 5 Days of Panacur (Fenbendazole) at 2x dosage • Kills everything • Good for new horses coming into your herd as treatment • Good for all horses moving to new area where there were no horses in the past

14. Pancur Powerpac

15. Panacur Powerpac

16. Benzimidazoles

17. Benzimidazoles • Effective control of following parasites: • Strongyloides (except benzelmin) • Ascarids • Large strongyles • Pinworms • NOT Bots • NOT Small Strongyles • Exception is Panacur PowerPak

18. Tetrahydropyrimidines • Say that 5 times fast… • Mimic activity of acetylcholine (a neurotransmitter that causes muscle contraction) • With tetrahydropyrimidines, contraction is permanent  rigid paralysis of parasite • Fastest activity of any deworming product • Only affect adult parasites (not larval stages) • Parasites bounce back quickly • Paste, suspension, and pelleted forms

19. Tetrahydropyrimidines

20. Tetrahydropyrimidines • Effective against the following parasites: • Ascarids • Large Strongyles • Small Strongyles • Pinworms • NOT effective for Bots • NOT effective for Strongyloides • Effective for tapeworms when given at twice the normal dosage

21. Heterocyclic Compounds • Only one used in horses (Piperazine) • Depolarizes muscle membranes – resistant to acetylcholine • Worms become paralyzed • Limited to adult parasites • Available only in powder and liquid (stomach tube), pelleted • Brand name: Piperazine (1X safety factor!)

22. Macrocyclic Lactones • Act on parasite’s nerve and muscle cells • Normal transmission of stimuli disturbed • Flaccid paralysis  inability to feed or swallow nutrients • Most potent killers! But, slow to act • Ability to kill external parasites • Lice, mites, ticks

23. Macrocyclic Lactones

24. Macrocyclic Lactones • Effective against the following parasites: • Strongyloides • Ascarids** • Large Strongyles • Small Strongyles (adult only – ivermectin; all stages - moxidectin) • Bots • Pinworms

25. Isoquinoline-Pyrazines • New kid on the block • NO ACTIVITY AGAINST NEMATODES! • Effective only against tapeworms • Disrupts worm’s outer layer  worm can’t maintain fluid balance • Generic name: Praziquantel • Brand names: Equimax, Quest Plus, ComboCare Gel, and Zimectrin Gold

26. Purge Deworming Sample Adult Horse Program (Maryland): • February: Deworm with Ivermectin + Praziquantel to kill bots and Tapeworms • April: Deworm with Moxidectin to kill encysted strongyles • August: Deworm with Ivermectin or Ivermectin + Praziquantel to kill bots and tapeworms • October: Deworm with Oxibendazole • December: Deworm with Ivermectin to kill bots

27. Problems with rotational deworming as we know it • Reasons for deworming often not known • Drug chosen may not be effective against parasite present in horse • Don’t discriminate between horses in different parts of the country (i.e. Florida vs. New York) • Horses vary widely in susceptibility to parasites

28. How should we deworm, then? • Target parasites • Tapeworm – once a year, during spring or autumn (more often for known problems) • Bots – must enter host prior to winter, deworm late autumn/early winter • Large strongyles • Most horse owners have unknowingly eradicated large strongyles already • Treat all horses at intervals of 6 months for 18 months • Small strongyles present greatest problem today

29. Targeting small strongyles • Objective of control • NOT to “kill worms” • Prevent contamination of environment with eggs • Kill female worms before they reproduce • Environmental factors • All horses pass strongyle eggs at a predictable time post-treatment • Infectivity of eggs is dependent upon environmental factors

30. Targeting small strongyles… • Environmental factors… • Northern states: • Hatching and development during spring, summer and autumn • Autumnwinter favorable for persistence! • Southern states: • Hatching and development during autumn and spring • Summer: development and survival poor; winter ok

31. Targeting small strongyles… • Host factors • Individual horses differ! • Routine deworming may be unnecessary for some horses in a herd • Categorize horses • Perform quantitative fecal examinations • Anthelmintic Issues • FECRT (Fecal Egg count Reduction Testing) • Know expected egg reappearance periods for the different compounds

32. Determining Strongyle Contaminative Potential • Requires fecal egg counts! • If horses haven’t been dewormed recently: • 20-30% = high egg counts • 30-50% = low egg counts • Less than 150 eggs per gram = Low Contaminators • Greater than 500 EPG = High Contaminators • Examine fecal samples 4 weeks after expiration of egg reappearance period

33. Expected Egg Reappearance Periods

34. Sample Schedule for Deworming • October – Moxidectin and Praziquantel for ALL horses • November, December, January, February – NOTHING (too cold) • March – FEC, identify contaminators • Ivermectin to all horses • April – NOTHING • May – FECRT • Strongid to moderate and high contaminators from March • Recheck fecal in 10-14 days • June – Strongid to high contaminators • July, August – NOTHING (too hot) • September – Strongid to moderate and high contaminators

35. Slow Rotation • A recommendation by some parasitologists • Rotate annually: • Moxidectin – year one • Strongid – year two • Ivermectin – year three • Panacur – year four

36. Deworming Protocols • Daily Dewormer: • Prevents damage done by immature worms migrating through internal organs • Few worms will survive to maturity  few to no worm eggs in manure  decreased likelihood of reinfestation of environment

37. Drawbacks of Daily Deworming • Active ingredient does not kill bots • You will have to give an ivermectin twice per year! • Light infestation may lead to natural immunity, dailies may prevent that • Not “natural” care even though no studies have shown any toxic effects • Accumulation over time?

38. Daily Dewormer Schedule • Spring Thaw: Ivermectin or Moxidectin to kill bots • Spring – early summer: daily dewormer • June 1: if tapeworms are a problem, double-dose of pyrantelpamoate or praziquantel • June 2 – killing frost: daily dewormer • Killing frost day: Ivermectin or moxidectin to kill bots • Day after – spring thaw: Daily dewormer

39. Anthelmintic Resistance • Drug resistance = ability of worms in a population to survive a treatment that once was effective against the same population • Same drug • Same dose • Same parasite • VERY common

40. Resistance • High mutation rate among some worms • Small number of resistant worms present • Deworm – kills off non-resistant worms • Resistant worms survive and reproduce, population grows

41. Does resistance exist in horse populations? • Small strongyles = most problematic internal parasites in horses • Wide range of symptoms • Rough hair coat • Poor growth • Suboptimal performance • Life-threatening chronic diarrhea, colic, and severe weight loss • Most effective control = deworming medications • Some small strongyles are resistant to dewormers!

42. Does resistance exist in horse populations? • Resistance to Panacur on 90% of the farms tested • 20% of farms - resistance to Strongid • No evidence of resistance to Ivermectin on any farm • Few farms were tested • Ivermectin resistance may exist elsewhere • Ivermectin-resistant parasites have been found in sheep and goats • Continue using ivermectin, moxidectin, and even pyrantel – check for resistance in your herd • No benefit to rotating dewormers with each treatment • Slow rotation recommended: one class per year

43. Management to control Parasites • Pasture Management! • Remove feces from congregation areas • Drag pastures regularly to break up manure • Do not overstock pasture! • Rotational grazing • Biological vacuum cleaners • Compost manure before spreading