1. Equine Parasites

2. General Considerations
Parasites are most successfully prevented through a combination of management and therapeutic strategies
Management
Decrease parasite burden in environment
Therapeutic
Deworming with proper product at proper intervals

3. Parasite Prevention Adequate pasture acreage Compost manure
Cleanliness
Pasture rotation
Mixed grazing (cattle and horses)

4. Pasture Rotation
Infective larvae on pasture decreases greatly over the winter and also in hot, humid days of summer
Move horses from old, infested pastures to ones that have minimal numbers of infective larvae
Deworm prior to moving
Foals and young horses should go to cleanest available pastures

5. Internal parasites
The amount of clinical disease a horse will show depends on three factors:
Type of parasite involved
Number of parasites involved
Host defenses. Young and debilitated animals more susceptible

6. Life Cycle of Parasites
Eggs
Larvae (immature worms)
Adults (mature worms)

7. Life cycle of the parasite
Eggs or larvae are deposited on the ground in the manure of infected horse
The eggs and larvae develop in the environment and are swallowed while the horse is grazing
Larvae mature in the horse’s digestive tract where most of them become egg laying adults.

8. Internal parasites – Common signs
Poor growth
Weight loss
Decreased feed efficiency
Colic
Diarrhea
Pneumonia
Death

9. Dull hair coat

10. Clinical sign – colic

11. Poor performance

12. Important 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)

13. Large Strongyle Strongylus vulgaris
Blood worm- bloodsucking of the large instestine
Most dangerous parasite of horses
Causes thromboembolic colic, various degrees of anemia.
Direct life cycle
Larvae live in artery supplying blood to the intestines. Blood clots form which block blood supply to the intestine

14. First 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.

15. 4th 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 ingestion
Collateral circulation

16. Life Cycle

17. Adult large strongyle

18. Strongylus vulgaris,adults in equine intestine “bloodworms”

19. After deworming “red worms”

20. This 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. 

21. S.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.

22. 3rd 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)

23. Large and small strongyle

24. Diagnosis
Diagnosis 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

25. Large Strongyles
Treat every 6 months
Use Ivermectin or monoxidecin

26. Small Strongyle- Cyathostominae
Numerous species of strongyles (40)
Direct Life cycle
Larvae life in gut wall of large intestine- therefore not as pathogenic as large stongyle
Cause damage to gut wall resulting in G.I. upset, and severe diarrhea.
Internal parasites of highest concern- encysted stage is not affected by dewormers
Very short life cycle 4 to 6 weeks

27. Life Cycle

28. Symptoms Colic Diarrhea Ill-thrift, loss of body condition
Subclinical diseases is more common and may result in greater economic losses

29. Diagnosis of Strongyles
Fecal flotation- small and
large stongyles look similar on float.
Assume the worst and treat for large
Necropsy

30. Encysted cyathostome larvae in the large colon of a horse.

31. Treatment
Many products available – nearly all horse wormers are effective against adults in the GI tract
Ivermectin, mixodectin, and fenbendazole effective against migrating larvae
Check fecal samples for eggs to gauge success of worming program

32. Control of strongyles Use effective wormers routinely
Avoid overgrazing pasture
Use clean pastures for young animals
Pile and compost manure
*No public health significance

33. Pinworms Oxyuris equi Adult pinworms lay eggs around the anus
Direct lifecycle
Eggs cause irritation and horses will rub their tails against objects
Bare patches around the tail and perineum- pruritus ani
Vague signs of abdominal discomfort if any
Controlled by most wormers

34. Life Cycle

35. Pinworms

36. Diagnosis of Pin Worms Egg masses in perineal region Tail rubbing
Eggs in feces (rare)
Adults in feces

37. Pinworms usually are the cause of the irritation that leads to tail rubbing. Adult females deposit adhesive egg masses on anal and perianal skin. Note the broken hair at the base of the tail.

38. Adults in feces

39. Control of Pin Worms
Thorough cleaning of stalls
Fresh food and water

40. Stomach bots Gastrophilus ssp
Insects – the adult is a fly, the larvae live in the horse’s stomach
Flies lay eggs on hair, they hatch and penetrate into the mouth tissue, then migrate to stomach
May cause stomach irritation and colic
G. nasalis, G. hemorrhoidalis, G. intestinalis

41. Life Cycle

42. Bot fly and egg

43. Bot fly larvae
Migrate 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.

44. gross lesion with adult worms, equine stomach

45. Mutual grooming leads to the ingestion of bot eggs by horses

46. Diagnosis of Bots See eggs on hair and mane Endoscopy of stomach
Necropsy
Knowing flies are in area

47. Treatment of Bots
Because flies are insects, only wormers that are effective against insects will kill bots
Ivermectin and moxidectin are effective
Nits can be removed from hair before they hatch
Nit removal combs, pumice stones
Warm water with insecticide added

48. Public health significance
Flies can lay eggs on human hair
Larvae will hatch and burrow into skin

49. The 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

50. Habronema
If 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 tissue
If the worms get deposited into the eye or the area around the eye it can cause a persistent case of conjunctivitis.

51. Cycle

52. Lesions

53. Ascarids - Roundworms Parascaris equorum
Most common in foals/young horses –can cause impactation and colic
Interfere with digestion and absorption of nutrients, notably protein
Cause telescoping of intestine in foals
Direct life cycle
Larvae migrate through lungs where they can cause pneumonia
Build up in large numbers in the anterior part of the small intestine

54. Parascaris equoru m
1 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.

55. Life Cycle

56. Ascarid
Can grow up to 12 inches in length within 4 weeks and block the small intestines.

57. Ascarids – Clinical Signs
Impaction colic – death
Pneumonia
Pot belly
Unthrifty appearance
Poor hair coat

58. Spaghetti for dinner??

59. Ascarid impactation and rupture

60. Parascaris equorum

61. Ascarid in the bile system of the liver

62. Diagnosis of ascarids
Clinical signs
Fecal flotation
Necropsy

63. Control of Ascarids Good sanitation
Eggs live in environment for many years
Avoid putting foals in same pastures year after year
Regular worming of foals and young stock

64. Treatment of Ascarids
Most 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

65. Tapeworms
Three species of tapeworms are found in horses: Anoplocephala magna , A perfoliata , and Paranoplocephala mamillana
Found mostly in the cecum but may also be in the small intestine.
Young and older horses more susceptible -mite
Difficult to detect on fecal exam.

66. Tape worms (Anaplocephala)
Cause colic
Live at ileo-cecal valve
Disrupt motility
Use prazinquantel

67. Difucult to detect the eggs on fecal sample

68. Infection of A. perfoliata with intussusception of the ileum into the cecum.

69. A cluster of tapeworm segments at the ileocecal valve are of the cecum of a naturally infected horse.

70. Thread worms Intestinal Threadworm
Strongyloides westeri – (strongyle-like)
Life cycle as short at 2 weeks
Infects young foals (2 weeks-6 months)
Larvae passed in mare’s milk to foals
May cause diarrhea in young foals
Immunity quickly developed
DOES NOT cause foal heat diarrhea
Strongyloides is zoonotic, cutaneous larva migraines, but not this species

71. Thread worms

72. Can be free living in the soil

73. Cutaneous larva migrans
Larva can penetrate foal’s skin to cause infection
May species penetrate human skin and cause problems in people as well

74. Diagnosis of Strongyloides
Fecal exam for larvae
Fecal culture
VERY rarely may see eggs

75. Stronglyoides egg (larvae moving)

76. Treatment of Strongyloides
Worm mare prior to foaling to prevent larval migration to udder
Worm foals at 4 weeks of age

77. Control of Strongyloides
Sanitation
Keep stall dry to kill larvae

78. Diagnosis of internal parasites
Fecal egg counts can be very helpful
negative fecal does not always mean no parasites
Monitor multiple horses on the farm at the same time
Some parasites are difficult to diagnose – tapeworms
Smear, float, centrifuge, and Baermann apparatus

79. Baermann apparatus
Lung worms

80. Dewormers 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 year
Avoid creating resistance to anthelmintics
*Double dose strongid
*Product containing prazinquantel

81. Dewormers Avermectins Ivermectin (Eqvalan, Zimectin, Equimectrin
Moxidectin (Quest)
Tetrahydropyrimidines
Pyrantal (Strongid, Rotation0
Benzimidazoles
Febendazole (Panacur, Safeguard)
Prazinquantel

82. Parasite control Manure removal at least 2x/week
Spread manure in hot weather away from fields where horses are grazing
Rotate Pasture- limit overgrazing (different species)
Group horses by age
Use feeder for hay and grain
Remove bot eggs from hair
Deworm new arrivals

83. Questions ??
CTVT pages ,
LACP pages