3 Parasitology in Practice

• This study note is on parasitology in practice

Lecture Outline

• Objectives cover Ascarids and Small Strongyles
• Includes anthelmintic information, covering 3 classes
• Two cases are presented, one Ascarid and another Small Strongyle
• How to manage ascarids in foals as well as small strongyles in adult horses is explained
• Two different farms will be presented

Objectives

• Determining Anthelmintic Resistance to Ascarids and also to Small Strongyles
• Identifying what anthelmintics to use
• Understanding and identifying high, moderate, and low shedders of small strongyles
• Deworming frequency is based on shedding level, especially in adult horses
• Recommendations are provided for foals relating to ascarids
• Suggested timings and products are shared for deworming foals

Controlling Parasites

• Understanding the current state of parasite control
• Determining who is responsible for deworming horses, either the owner or a vet
• Knowing the current recommendations for parasite control

Historical Deworming - 1966

• Deworming occurred every 2-4 months
• Dewormers were rotated between classes
• The entire herd was dewormed
• Foals were dewormed at birth using ivermectin and then every month

Anthelmintics

• Benzimidazoles are a class of anthelmintic
• Fenbendazole, like Panacur®, is an anthelmintic
• Panacur Power Pack® involves a 2x dose for 5 days, effective against encysted small strongyles, dosed at 10 mg/kg, or 2x
• Oxibendazole, like Anthelcide®, is a anthelmintic
• Pyrantel is an anthelmintic
• Strongid-P® is pyrantel pamoate
• Strongid-C is pyrantel tartrate - The difference is C is for daily deworming and P is a paste
• Macrocyclic lactones are a class of anthelmintic
• Ivermectin is for luminal stages of small strongyles
• Moxidectin (Quest®) is labeled for encysted small strongyles
• Praziquantel may combined with other anthelmintics

Resistance and Refugia

• Decades of intensive deworming has resulted in resistance, specifically in Ascarids and Small Strongyles
• There are currently no new anthelmintic drugs on the horizon
• Veterinarians needs to play a key role in development of deworming programs
• Refugia is the proportion of parasites not exposed to chemical control
• Promoting refugia is desirable
• This can be done by decreasing the frequency of deworming
• The goal of anthelmintic treatment is not to eliminate all parasites
• Reducing environmental shedding and tolerating some egg shedding is necessary

Fecal Testing and Resistance

• Fecal Egg Counts (FEC) are a quantitative measure, recorded as # eggs/gram of feces
• Two methods for FEC are McMasters and Wisconsin
• Environmental contamination is a factor in fecal testing
• There is not always a good correlation between the count and worm burden when counts are low
• A "Splash" is around 110 EPG (low)
• Qualitative fecal tests are more sensitive and useful for pinworms and tapeworms
• Quantitative Fecal Egg Counts are useful to help identify the level of egg shedding: Low, Moderate & High
• Quantitative Fecal Egg Counts are effective in adult horses over 2 years
• Effective for small strongyles and determining when to deworm
• Fecal Egg Count Reduction (FECR) is a measure of resistance
• FECR involves performing a FEC, a Quantitative Egg count pre Rx, repeating 1-2 weeks post deworming
• An effective anthelmintic will have a FECR > 90-95%

Triston Case Study

• Triston was a 6 month old Shire colt
• He had a previous history of ruptured bladder and colitis at birth, including incisional dehiscence and colitis
• There were no problems since discharge
• He was dewormed every 2 months with ivermectin or strongid
• Triston experienced colic for 10 hours
• He was treated with Banamine, Xylazine, and Butorphanol
• He had a heart rate > 90 bpm and a temperature of 102.2 F
• He had a distended small intestine and 5 L of net reflux
• Mild leukopenia (4,000 cells/ul), mild dehydration, and serosanginous fluid from a belly tap with mild increase in protein (2.9 gm/dl) but normal WBC
• Differentials included enteritis (fever, low WBC) and adhesion (previous surgery)
• He was initially treated medically with repeated doses of Xylazine but then taken for surgery due to uncontrollable pain
• All the parasites were not able to be removed during surgery
• Concerned about ileus post-op and some problems with ascarids plugging the tube and no significant net reflux
• Triston was treated with antibiotics, NSAIDs, and fluids then dewormed with FBZ initially at 2.5 mg/kg PO once, then 5 mg/kg PO once, and finally 10 mg/kg PO q 5 days
• He did well and was discharged in 4 days
• Triston experienced colic again 2 months post-op and was euthanized
• The cause was assumed to be adhesions
• Triston had a high parasite burden despite owner deworming every 2 months because of resistance
• Triston's death was due to complications of ascarid impaction

Ascarid Resistance and Recommendations

• Ivermectin and moxidectin resistance are widespread
• Pyrantel resistance exists in some areas
• Fenbendazole resistance has not yet been reported
• High parasite burden can result in significant problems in foals
• Macrocyclic lactones (Ivermectin & moxidectin) have widespread resistance, since 2000, including World-wide
• Pyrantel Pamoate resistance has been reported in certain areas in NA, potentially due to use of Strongid-C
• Resistance has not been reported with Benzimidazoles, but higher doses must be used, like 10 mg/kg FBZ as opposed to 5 mg/kg, but it is less effective on immature parasites
• Stop deworming foals at birth because S. westeri is uncommon
• Deworm when parasites approach maturity during the prepatent period of 10-12 weeks, around 60-70 days of age using fenbendazole at 10 mg/kg
• Deworm every 60 days, not more frequently using fenbendazole at 10 mg/kg, as there is no resistance yet
• Strongyles are a problem for weanlings (6 months of age) and will need to be treated with ivermectin or moxidectin, however, moxidectin is not for foals < 4 months

Determining Resistance and Summary for Young Horses

• Resistance can also be tested in Ascarids using FECR
• Collect feces before & 2 week post deworming
• Egg shedding (high, mod, low) is not effective for young horses
• Ascarids should be treated, using FBZ starting at 2 months(and repeat every 2-3 months), until at least 1.5 - 2 years of age
• Small strongyles are a problem at 5-6 months
• Treat Small strongyles using Ivermectin or moxidectin if > 4 months age
• Deworm Small strongyles as high shedders until > 2 years of age

Adult Horses - Deworming Programs

• These programs should be for horses > 2 years of age
• Programs should focus on small strongyles
• In 1966 recommendations were to treat every horse on farm every 60 days using rotation of anthelmintics
• This was very effective for large strongyles who were most important
• Currently, large strongyles have been almost eradicated in well managed farms
• Widespread resistance is present in small strongyles

Splash Case Study

• Splash was a 2 year old Paint Mare who presented with weight loss, diarrhea, and an unknown deworming history
• She had Hypoalbuminemia and Hyperglobinemia on CBC & Chem
• Fecal exams showed qualitative 2+ strongyle type but a Quantitative 110 EPG Strongyle type, considered low
• It was found that the immature worm populations were not producing oocytes
• The diagnosis was Cyathostomiasis

Small Strongyles - Resistance

• 95% are resistant to Benzimidazoles/FBZ in the South Eastern US

• The same study showed 50% of farms are resistant to pyrantel
• Avermectins still seem to work

Recommendations

• Only use anthelmintics that are effective on the target parasite
• Try to reduce # times dewormed
• Horses should be dewormed as individuals
• Recommendation #1 for adult horses is to perform quantitative fecals on all adult horses to determine shedding category
• Low shedder: < 200 EPG - 50% of herd
• Moderate shedder: 200-500 EPG
• High shedder: > 500 EPG (20% of herd)
• Shedding categorization is genetically determined & consistent
• Cushing's horses increase shedding
• Horses with Heaves (RAO) have shown low shedding in some studies
• High shedders should be dewormed more frequently than low shedders
• Another recommendation is to determine if there is resistance using a Fecal egg count reduction test
• Should be done pre and 2 weeks post deworming
• Test horses > 200 EPG, but all horses do not have to be tested, a subset is sufficient
• Effective anthelmintics should reduce egg counts by 90-95% post deworming, test should be repeated yearly
• Avoid use of ineffective anthelmintic

Egg Reappearance Periods

• Fenbendazole (Panacur) / Oxibendazole (Anthelcide) / Pyrantel: 4 weeks
• Ivermectin : 6-8 weeks
• Moxidectin: 12 weeks
• A Deworming Program should use the egg reappearance periods
• Combination deworming will increase efficacy, consult vet for best timing

Farm 1 and Farm 2 case studies

• Farm #1 is a horse farm/rescue with 52 adult horses present on farm including miniature horses, draft horses, and light breed horses
• It is a closed herd with occasional deworming performed
• Has facilities of 40 acres, dry lots, barn with stalls, and pasture
• Farm 1 practices of Physical exams & Fecal sample collection. using Qualitative and quantitative fecal exam
• High Shedders are defined at >500 EPG, Moderate Shedders (200-500 EPG), and Low Shedders (<200 EPG)
• Deworming involves ivermectin
• Farm #2 is a private horse farm with ~40 horses total who are a range of weanlings, yearlings, and adults
• The horses are Housed in pastures, dry lots and stalls
• Fillies and colts in separate pastures, fed round hay bales with grain, but No vaccinations given
• They are Dewormed – End of August using Fenbendazole 10 mg/kg PO q 24 hrs for 5 days

Lady Sparrow Case Study

• Lady Sparrow was presented VHC 9/17/13 showing 2/9 on the body score scale
• A neurological exam determined she was weak, but showed No cranial nerve/proprioceptive deficits
• She had No vaccines given, Owner concerned about West Nile
• Diagnostics showed hematocrit was 31, total protein 5.2, and albumin 2.3
• She was treated with 5 L LRS and Flunixin meglumine
• Upon discharge, She was given more Flunixin meglumine, Vitamin E, and SMZ
• A Field Call 9/18/2013 showed recheck of Lady Sparrow and Evaluation of yearling filly pasture
• 1 filly was found dead in pasture and was named Turtle Bay with a BCS of 2/9 which was Submitted for necropsy
• All other tested all fillies showed very low normal levels, indicating disease
• 102.2 F Elegonza with had a heart rate of 84 and respiration rate of 24 -She also showed a BCS or 3/9 and categorized as depressed
• Snow Sprite showed 101.3 heart rate of 92 and a respiration rate of 30
• She showed 1/9 and categorized as depressed
• Velvet showed 101.7 heart rate of 64 and a respiration rate of 20
• She also showed a BCS or 3/9 and categorized as depressed
• All fillies showed some parasite, which some showing heavy levels of parasites
• The diagnosis for Yearling Fillies were to have weight loss and anemia suspected of small strongyles
• They were treated with ivermectin which later showed Moxidectin/Praziquantal, and Flunixin Meglumine
• Oral iron product (Red Cell) and sucralfate was additionally given to the yearling fillies

Farm Cases Recommendations and Summary

• Implement a parasite control program for Yearling Fillies
• Deworm them as High Shedders horses < 2 years of age, including Fecal egg reduction test
• Consider doing FEC 2-3 weeks post deworming to look for resistance
• Farm #1 has no young horses, so they should only Deworm based type of shedders
• Farm #2 has a Large number of young horses, so they should always Deworm those horses as high shedders until > 2 years of age
• Possible Downsides of Less Frequent Deworming include the potential for large strongyles to become a problem again and the potential of other parasites due to less frequent deworming