Podcast
Questions and Answers
Why has regular and intensive deworming in equine medicine led to a significant challenge in parasite control?
Why has regular and intensive deworming in equine medicine led to a significant challenge in parasite control?
- It has caused an increase in the population of beneficial gut bacteria, disrupting the equine digestive system.
- It has eradicated most common parasites, leading to a reliance on fewer drug options.
- It has fostered the development of resistance in parasites to many available anthelmintics. (correct)
- It has decreased the overall worm burden in horses, making diagnosis more difficult.
How does the concept of 'refugia' contribute to strategies for managing anthelmintic resistance in equine parasite control?
How does the concept of 'refugia' contribute to strategies for managing anthelmintic resistance in equine parasite control?
- Refugia focuses on using broad-spectrum anthelmintics to target all stages of parasite development.
- Refugia encourages the constant rotation of anthelmintic drugs to prevent resistance development.
- Refugia aims to ensure that a proportion of the parasite population remains unexposed to anthelmintic drugs. (correct)
- Refugia involves the complete removal of horses from pasture environments to break the parasite lifecycle.
What is the primary goal of anthelmintic treatment in modern equine parasite management?
What is the primary goal of anthelmintic treatment in modern equine parasite management?
- To select for anthelmintic-resistant parasite populations, ensuring long-term control options.
- To completely eradicate all parasites from the horse's system to ensure optimal health.
- To reduce environmental shedding of parasite eggs, while tolerating some level of parasite presence. (correct)
- To eliminate environmental shedding to reduce the reliance on anthelmintic treatments.
Why are fecal egg counts (FEC) considered inconsistent for detecting tapeworm and pinworm infections in horses?
Why are fecal egg counts (FEC) considered inconsistent for detecting tapeworm and pinworm infections in horses?
How can quantitative fecal egg counts aid in equine parasite control beyond simply identifying patent infections?
How can quantitative fecal egg counts aid in equine parasite control beyond simply identifying patent infections?
What is the significance of monitoring strongyle egg counts in individual horses over extended periods (e.g., > 2 years)?
What is the significance of monitoring strongyle egg counts in individual horses over extended periods (e.g., > 2 years)?
Why is a pre-treatment fecal egg count of greater than 200 EPG necessary for an accurate FECR?
Why is a pre-treatment fecal egg count of greater than 200 EPG necessary for an accurate FECR?
What does a Fecal Egg Count Reduction (FECR) of greater than 90-95% typically indicate regarding anthelmintic efficacy?
What does a Fecal Egg Count Reduction (FECR) of greater than 90-95% typically indicate regarding anthelmintic efficacy?
What is the primary reason that Parascaris equorum infections pose a significant threat to young horses?
What is the primary reason that Parascaris equorum infections pose a significant threat to young horses?
Why is the long-term prognosis for horses requiring surgery due to ascarid impactions often poor?
Why is the long-term prognosis for horses requiring surgery due to ascarid impactions often poor?
How does the life cycle of Parascaris equorum contribute to the challenge of controlling these parasites in equine populations?
How does the life cycle of Parascaris equorum contribute to the challenge of controlling these parasites in equine populations?
What factors might explain the reported ascarid resistance to pyrantel pamoate in Texas and Kentucky farms, but its lower prevalence elsewhere?
What factors might explain the reported ascarid resistance to pyrantel pamoate in Texas and Kentucky farms, but its lower prevalence elsewhere?
Why is P. equorum considered a 'dose-limiting parasite' in equine deworming protocols?
Why is P. equorum considered a 'dose-limiting parasite' in equine deworming protocols?
How does the efficacy of anthelmintics against Parascaris equorum differ between mature and immature parasite populations, and what implications does this have for treatment strategies?
How does the efficacy of anthelmintics against Parascaris equorum differ between mature and immature parasite populations, and what implications does this have for treatment strategies?
What is the rationale behind delaying the first deworming of foals until 60-70 days of age in the context of Parascaris equorum control?
What is the rationale behind delaying the first deworming of foals until 60-70 days of age in the context of Parascaris equorum control?
What is the purpose of performing fecal egg counts two weeks post-treatment when assessing anthelmintic resistance?
What is the purpose of performing fecal egg counts two weeks post-treatment when assessing anthelmintic resistance?
Why might benzimidazole drugs be considered the preferred anthelmintic class for treating heavily infected foals suspected of ascarid resistance?
Why might benzimidazole drugs be considered the preferred anthelmintic class for treating heavily infected foals suspected of ascarid resistance?
How does fenbendazole, administered at 10 mg/kg PO q 5 days, function as a larvicide in preventing the introduction of resistant ascarids on farms?
How does fenbendazole, administered at 10 mg/kg PO q 5 days, function as a larvicide in preventing the introduction of resistant ascarids on farms?
What environmental factors primarily influence the lifecycle and transmission of small strongyles in equine populations?
What environmental factors primarily influence the lifecycle and transmission of small strongyles in equine populations?
How does the encystment of small strongyle larvae within the horse's intestinal wall contribute to the challenge of controlling these parasites?
How does the encystment of small strongyle larvae within the horse's intestinal wall contribute to the challenge of controlling these parasites?
Flashcards
What is Refugia?
What is Refugia?
The ability of parasites to survive exposure to chemical control (dewormers).
What is a Fecal Egg Count?
What is a Fecal Egg Count?
A test that detects and counts parasite eggs in feces, indicating patent infections.
What does FECR require?
What does FECR require?
FECR requires quantitative fecal egg counts before and 7-14 days after anthelmintic treatment.
What is an Ascarid infection?
What is an Ascarid infection?
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What is the Ascarid Lifecycle?
What is the Ascarid Lifecycle?
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When are anthelmintics most effective against ascarids?
When are anthelmintics most effective against ascarids?
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What are the clinical signs of Small Strongyles infection?
What are the clinical signs of Small Strongyles infection?
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What is the Lifecycle of Strongyles?
What is the Lifecycle of Strongyles?
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What is the Recommendation for Horses Age > 2?
What is the Recommendation for Horses Age > 2?
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Study Notes
Parasite Control - The New Role of Veterinarians
- Decades of intensive deworming have led to anthelmintic resistance in equine medicine, specifically in small strongyles and ascarids
- There are only 3 anthelmintic groups available: benzimidazoles, macrocyclic lactones (ivermectin and moxidectin), and pyrantel salts
- No new anthelmintic drugs are expected soon
- Veterinarians need to advise clients on deworming practices to prevent further resistance
General Recommendations for Resistance/Prevention
- Refugia is the proportion of parasites not exposed to chemical control
- The goal is to reduce environmental shedding, so some fecal egg shedding should be tolerated
- Fecal floatation shows patent infections
- Fecal egg counts are inconsistent for tapeworms and pinworms
- Qualitative fecal egg counts are more sensitive than quantitative counts in certain cases
- Quantitative fecal egg counts indicate environmental contamination
- Immature worm populations have a poor relationship between worm burden and egg count
- Strongyle egg counts are consistent in individual horses (> 2 years) over time
Fecal Egg Count Reduction (FECR)
- FECR requires quantitative fecal egg counts before and 7-14 days after anthelmintic treatment
- Testing more horses improves estimation, with pre-treatment fecal egg counts preferably > 200 EPG
- FECR is calculated as: (Meanpretreatment – Meanposttreatment)/ MeanPretreatment x 100
- FECR > 90 to 95% indicates acceptable efficacy
Ascarids
- Parascaris equorum infections are common in young horses and are highly pathogenic in horses less than 1 year old
- Clinical signs include poor growth, ill-thrift, and life-threatening impactions
- Horses with ascarid impactions may show colic, nasogastric reflux, fever, and a distended small intestine
- Recent deworming is often reported with infections
- Treatment may be medical or surgical, but long-term prognosis is poor
- The lifecycle starts with ingestion of larvated eggs, which hatch in the small intestine and migrate through the liver and lung.
- Larvae are then coughed up and swallowed before maturing in the small intestine
- The prepatent period is 75-80 days
- Most horses develop immunity, and ascarids are rare in horses > 2 years old
Historical Deworming Practices and Resistance
- Administering ivermectin for suspected Strongyloides westeri infections in foals less than 1 month old has been common
- Foals are often dewormed every 30 days with ivermectin
- Macrocyclic lactone resistance is now common
- Ascarid resistance to pyrantel pamoate has been reported in Texas and Kentucky
- Pyrantel resistance is less common outside of North America
- Daily Strongid C use may influence resistance development
- Ascarids are not yet resistant to benzimidazoles
Recommendations and Key Points for Ascrarids
- P. equorum is harder to kill, acting as a dose-limiting parasite
- Fenbendazole is dosed at 5 mg/kg for strongyles and pinworms, but 10 mg/kg for equine ascarids
- Anthelmintics are more effective against mature ascarids, for example oxibendazole (10 mg/kg) is 94-100% effective in patent infections but has 44% efficacy in immature infections (28 days post infection)
- Reduce anthelmintic treatments, with first deworming no earlier than 60-70 days of age
- Repeat treatments should be 60 days apart, and some fecal egg shedding should be tolerated
- Determine resistance annually, especially on broodmare farms, using FECR counts or by checking fecal egg counts 2 weeks post treatment
- Ivermectin or moxidectin is indicated for other parasites even with roundworm resistance, though moxidectin is not for foals < 4 months
- For heavily infected foals, benzimidazole is recommended, which starves ascarids by interfering with beta-tubulin synthesis, or a smaller dose of fenbendazole (5 mg/kg) with mineral oil
- Prevent resistant ascarids by using fenbendazole at 10 mg/kg PO q 5 days, which is larvicidal, in instances when mares and foals return from a broodmare farm and isolate them for 3 days after deworming
Small Strongyles
- Clinical signs range from none to subclinical to acute diarrhea and protein loss
- Small strongyle infections are less clinically significant than ascarid infections
- Strongyles are transmitted on pastures
- Strongyle eggs hatch in temperatures of 45-85F, and larvae mature into the infective L3 stage
- Hatched larvae die in hot weather (> 90F), but can survive freezing
- Transmission is perennial in northern climates
- New larval development occurs between 45-85 F
- Small strongyle larvae invade the lining of the cecum and large colon after ingestion, and remain for a few weeks or up to 2.5 years
- The synchronous mass emergence of encysted small strongyles results in clinical disease
- Adult strongyles then develop in the lumen of the large intestine
Resistance With Small Strongyles
- Fenbendazole at 5 mg/kg has widespread resistance in adults
- Fenbendazole at 10 mg/kg q 5 days is effective for adults and larvicidal for some encysted small strongyles but may become ineffective
- Oxibendazole at 10 mg/kg has some adult populations reporting resistance
- Pyrantel pamoate (Strongid P) at 6.6 mg/kg has some adult populations reporting resistance
- Pyrantel tartate (Strongid C) at 2.64 mg/kg daily has some populations that are resistant and includes the L3 stage
- Ivermectin at 0.2 mg/kg has reduced activity with immature luminal stages and earlier egg shedding in some populations
- Moxidectin at 0.4 mg/kg is effective against some stages of encysted but has reports of reduced activity with immature luminal stages and earlier egg shedding in some populations
Recommendations (for horses > 2 years of age)
- Perform fecal egg counts to determine if horses are low (< 200 EPG), moderate (200-500 EGP), or high (> 500 EGP)
- High shedders should be dewormed more frequently than low or moderate shedders
- Deworm more frequently in the Spring-Fall months
- Perform FECR to determine if resistance is present, using horses with a fecal egg count > 200 EPG
- FECR should be done yearly, if resistance is present anthelmintic should be eliminated from use to control small strongyles
Summary
- Many farms will be unable to complete fecal egg counts with FECR
- Consider testing a portion of horses because some information is better than no information
- Ascarid infections in foals can result in significant mortality and morbidity
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