2General Considerations Parasites are most successfully prevented through a combination of management and therapeutic strategiesManagementDecrease parasite burden in environmentTherapeuticDeworming with proper product at proper intervals
4Pasture RotationInfective larvae on pasture decreases greatly over the winter and also in hot, humid days of summerMove horses from old, infested pastures to ones that have minimal numbers of infective larvaeDeworm prior to movingFoals and young horses should go to cleanest available pastures
5Internal parasitesThe amount of clinical disease a horse will show depends on three factors:Type of parasite involvedNumber of parasites involvedHost defenses. Young and debilitated animals more susceptible
6Life Cycle of Parasites EggsLarvae (immature worms)Adults (mature worms)
7Life cycle of the parasite Eggs or larvae are deposited on the ground in the manure of infected horseThe eggs and larvae develop in the environment and are swallowed while the horse is grazingLarvae mature in the horse’s digestive tract where most of them become egg laying adults.
8Internal parasites – Common signs Poor growthWeight lossDecreased feed efficiencyColicDiarrheaPneumoniaDeath
12Important Parasites in the horse Large strongyle (Stongylus vulgaris, S.edentatus, S.equinus)Small strongyle (Cyathostemes)Round worm (Ascarids)Bots (Gastrophilus spp)Pin worms (Oxyuris equi)Tapeworms (Anoplochephala)Threadworm (Strongyloides)
13Large Strongyle Strongylus vulgaris Blood worm- bloodsucking of the large instestineMost dangerous parasite of horsesCauses thromboembolic colic, various degrees of anemia.Direct life cycleLarvae live in artery supplying blood to the intestines. Blood clots form which block blood supply to the intestine
14First stage is the egg in feces or soil, molts to 2nd stage in feces or soil. 3rd stage becomes “sheathed” or sticks to walls, buckets, etc.When ingested by the horse the infective 3rd stage larvae of S.vulgaris cast off there sheath in the lumen of the s. intestine and enter the wall of the cecum and ventral colon. They curl up under the mucous membrane and prepare to molt. After 8 days the molt is complete and become a 4th stage larva and resume migration.
154th stage penetrate nearby small arterioles and wanders to the cranial mesenteric artery, which supplies blood to the instestine. (this leaves a path of inflammation, which can lead to thrombosis or occlude the vessel) After 2-4 months they enter the surrounding tissue of the intestinal wall and a final molt takes place and the immature adults (5th stage) enter the lumen of the cecum and ventral colon , mature and reproduce 6 months after original ingestionCollateral circulation
20This verminous arteritis lesion is from the cranial mesenteric artery of a weanling Quarter Horse colt. Verminous arteritis is caused by the migration of larvae of Strongylus vulgaris through the blood vessels. It was once a common cause of colic and death in domestic horses.
21S.edentatus, S. equinus 2 times as large as adults The 3rd stage of S. edentatus migrate to the liver, become encapsulated and molt to the 4th stage in approx. 2 weeks. After molting the larvae wander aimlessly in the liver for 2 months, leave the liver by ligaments that hold the liver in position, wander for months in the connective tissues, and 11 months (PPP) after ingestion can be found in the lining of the cecum and colon.
223rd stage S.equinus encyst and undergo molt in the wall of the large intestine. After molting they bore into the right half of the liver which lies in contact with this portion of the large intestine. They stay for 6-7 weeks, enter the pancreas and abdominal cavity where the complete their development to adults. Reenter the lumen of the large intestine and mate. (9mo. PPP)
24DiagnosisDiagnosis of mixed strongyle infection is based on demonstration of eggs in the feces. Specific diagnosis can be made by identifying the infective larvae after fecal
25Large StrongylesTreat every 6 monthsUse Ivermectin or monoxidecin
26Small Strongyle- Cyathostominae Numerous species of strongyles (40)Direct Life cycleLarvae life in gut wall of large intestine- therefore not as pathogenic as large stongyleCause damage to gut wall resulting in G.I. upset, and severe diarrhea.Internal parasites of highest concern- encysted stage is not affected by dewormersVery short life cycle 4 to 6 weeks
28Symptoms Colic Diarrhea Ill-thrift, loss of body condition Subclinical diseases is more common and may result in greater economic losses
29Diagnosis of Strongyles Fecal flotation- small andlarge stongyles look similar on float.Assume the worst and treat for largeNecropsy
30Encysted cyathostome larvae in the large colon of a horse.
31TreatmentMany products available – nearly all horse wormers are effective against adults in the GI tractIvermectin, mixodectin, and fenbendazole effective against migrating larvaeCheck fecal samples for eggs to gauge success of worming program
32Control of strongyles Use effective wormers routinely Avoid overgrazing pastureUse clean pastures for young animalsPile and compost manure*No public health significance
33Pinworms Oxyuris equi Adult pinworms lay eggs around the anus Direct lifecycleEggs cause irritation and horses will rub their tails against objectsBare patches around the tail and perineum- pruritus aniVague signs of abdominal discomfort if anyControlled by most wormers
39Control of Pin WormsThorough cleaning of stallsFresh food and water
40Stomach bots Gastrophilus ssp Insects – the adult is a fly, the larvae live in the horse’s stomachFlies lay eggs on hair, they hatch and penetrate into the mouth tissue, then migrate to stomachMay cause stomach irritation and colicG. nasalis, G. hemorrhoidalis, G. intestinalis
43Bot fly larvaeMigrate thru the tongue and esophagus after they are ingested, and attach themselves to the lining of the stomach, where they stay for up to 11 months. In large numbers, they contribute to gastric (stomach) ulcers and occasionally rupture of the stomach.
45Mutual grooming leads to the ingestion of bot eggs by horses
46Diagnosis of Bots See eggs on hair and mane Endoscopy of stomach NecropsyKnowing flies are in area
47Treatment of BotsBecause flies are insects, only wormers that are effective against insects will kill botsIvermectin and moxidectin are effectiveNits can be removed from hair before they hatchNit removal combs, pumice stonesWarm water with insecticide added
48Public health significance Flies can lay eggs on human hairLarvae will hatch and burrow into skin
49The stomach worms Habronema muscae H microstoma , and Draschia megastoma The adults are 6-25 mm in size. Draschia are found in tumor-like swellings in the stomach wall.The eggs or larvae are ingested by larvae of house or stable flies, which serve as intermediate hosts. Horses are infected by ingesting flies that contain infective larvae or by free larvae that emerge from flies as they feed around the lips
50HabronemaIf the larvae which are in the mouthparts of the immediate host are deposited in the open skin well the fly feeds it can cause summer sores.Summer sores are ulcerated irritations. These lesions can cause soreness and itchiness and become covered in a reddish-yellow tissueIf the worms get deposited into the eye or the area around the eye it can cause a persistent case of conjunctivitis.
53Ascarids - Roundworms Parascaris equorum Most common in foals/young horses –can cause impactation and colicInterfere with digestion and absorption of nutrients, notably proteinCause telescoping of intestine in foalsDirect life cycleLarvae migrate through lungs where they can cause pneumoniaBuild up in large numbers in the anterior part of the small intestine
54Parascaris equoru m1 celled egg in feces (1-2 weeks) Infective eggs are swallowed, they hatch and liberate infective 2nd stage larvae, which burrow into the wall of the small intestine and are carried to the liver by the portal vein. After migrating through the liver tissue, they enter the hepatic vein and are carried by the posterior vena cava to the lungs, where they break the into the alveoli, molt and are coughed up and swallowed, returning to the small intestine to mature. (3months) Eggs have proteinaceous layer and is sticky. Eggs adhere to stall walls, mangers, buckets, etc.
62Diagnosis of ascaridsClinical signsFecal flotationNecropsy
63Control of Ascarids Good sanitation Eggs live in environment for many yearsAvoid putting foals in same pastures year after yearRegular worming of foals and young stock
64Treatment of AscaridsMost common wormers are effective against ascarids (Safeguard, Panacur, Strongid, Ivermectin)If a foal has a very heavy infection it should be wormed with less effective products to prevent impaction
65TapewormsThree species of tapeworms are found in horses: Anoplocephala magna , A perfoliata , and Paranoplocephala mamillanaFound mostly in the cecum but may also be in the small intestine.Young and older horses more susceptible -miteDifficult to detect on fecal exam.
66Tape worms (Anaplocephala) Cause colicLive at ileo-cecal valveDisrupt motilityUse prazinquantel
68Infection of A. perfoliata with intussusception of the ileum into the cecum.
69A cluster of tapeworm segments at the ileocecal valve are of the cecum of a naturally infected horse.
70Thread worms Intestinal Threadworm Strongyloides westeri – (strongyle-like)Life cycle as short at 2 weeksInfects young foals (2 weeks-6 months)Larvae passed in mare’s milk to foalsMay cause diarrhea in young foalsImmunity quickly developedDOES NOT cause foal heat diarrheaStrongyloides is zoonotic, cutaneous larva migraines, but not this species
76Treatment of Strongyloides Worm mare prior to foaling to prevent larval migration to udderWorm foals at 4 weeks of age
77Control of Strongyloides SanitationKeep stall dry to kill larvae
78Diagnosis of internal parasites Fecal egg counts can be very helpfulnegative fecal does not always mean no parasitesMonitor multiple horses on the farm at the same timeSome parasites are difficult to diagnose – tapewormsSmear, float, centrifuge, and Baermann apparatus
80Dewormers None are 100% effective 2 month interval (6 times a year) *think life cycles*Use a broad spectrum product as basis for control (ivermectin, moxidectin)Be sure to treat for tapeworms 1-2 time per yearAvoid creating resistance to anthelmintics*Double dose strongid*Product containing prazinquantel
82Parasite control Manure removal at least 2x/week Spread manure in hot weather away from fields where horses are grazingRotate Pasture- limit overgrazing (different species)Group horses by ageUse feeder for hay and grainRemove bot eggs from hairDeworm new arrivals