Review of the Common Internal Parasites of Swine

1. Review of the Common Internal Parasites of Swine

2. Introduction: Most parasitic infections of swine will be diagnosed by finding the adult or larval parasites or the lesions they produce while performing a necropsy. However, in reviewing the common spp. Of swine parasites, a characteristic egg has also been included. If a more thorough explanation of the “Salient Points”, or “Feature of the Life Cycle” is necessary, please see your corresponding lecture notes from the second year or appropriate texts.

3. Unembryonated egg of Ascaris suum: (50-75 um x 40-50 um) -eggs are unembryonated in fresh feces, oval, brownish and possess an irregular albuminous coat. Occasionally unfertilized eggs are passed which vary in shape and lack the irregular coat.

4. Embryonated eggs of Ascaris suum: When allowed to stand for a time at room temperature, eggs may contain larvae.

5. Life Cycle features of Ascaris suum: The infective stage (L2) occurs in the eggs which hatch upon ingestion. Tissue migrations follow the hepaticotracheal route and may be completed as early as 10 days. Resulting L4 larvae molt and mature to egg producing adults in 43-50 days. Most worms are expelled by 23rd week of patency.

6. Adult Ascaris suum: heavy infection Large numbers of adult worms adult may occlude or perforate the gut. Migration into the bile duct has been reported. This migration may occur after treatment.

7. Gross liver lesions These are produced by host response to migrating larvae and maycause considerable loss at slaughter due to condemnations. The majority of these may resolve in a period of 25- 40 days. Some heavy infections may be found in the intestines without any visible liver damage.:

8. Lungs of an 11-week-old pig: with chronic pneumonia and heavy ascarid infection. “Thumps or a soft moist cough which occurs early (7 – 10 days) after ascarid has been attributed to migrating larvae. This point has been questioned by some authors.

9. Ascaris suum: Salient points Review of the main features of A. suum infections including Rx- Piperazine salts, dichlorvos, fenbendazole, ivermectin, levamisole, and pyrantel. Hygromycin and pyrantel can be used in feed as prophylatics.

10. Oesophagostomum spp. Egg(73 – 89u x 34 – 45u) These eggs are typical thin-shelled strongyle-type eggs and are similar to the eggs of the red stomach Hyostrongylus.

11. Oesophagostomumnodules in large intestine. These worms are very common in older swine, infection occurs by ingestion of third stage larvae which encyst in nodules later to emerge as L4. The prepatent period is 23 - 53 days according to species.

12. Oesophagostomum : salient points: The nodular worm of swine are generally considered non-pathogenic although very heavy infections may cause G.I. disturbances.Rx:piperazine salt, TBZ. levamisole. fenbendazole, ivermectin. Dechlorvos, and pyrantel.

13. Strongyloides ransomi:eggs (45-55 u. x 26-35 um) eggs are similar to other Strongyloides sp. , thin-walled and larvated.

14. Life cycle features of Strongyloides ransomi: Three routes of infection occur, prenatal, transcolostral and percutaneous( lung migration). Prepatent periods are very short ( 2 – 10 days)

15. Section of pig intestine showing location and small size of adult worms.

16. Comparison of litter mate pigs: Heavy infections of Strongyloides, may be fatal or severly affect growth

17. Strongyloides: salient points The earliest parasitic infection producing signs in very young animals. Rx – TBS, levamisole.

18. Trichuris suis egg: ( 50 – 60u x 21 – 25 u) Trichuroid egg with mucoid plugs. These are common worms of swine

19. Trichuris suis adults: in pig cecum Like all whipworms the thin anterior end is embedded in the mucosa. Heavy infections have been reported to cause necrosis, edema, hemorrhage, ulcerlike lesions and nodule formation in the cecum and colon, but these are generally considered to be rare.

20. Trichuris suis: salient points Characteristics are similar to those of other whipworms, direct life cycle. Rx – dichlorvos, fenbendazole.

21. Stomach worms Three species of stomach worms commonly occur in swine: a. Hyostrongylus rubidus: “red” stomach worm ( a trichostrongyle) b. Ascarops strongylina: “thick” stomach worm ( a spirurid) c. Physocephalus sexalatus: “thick” stomach worm ( a spirurid

22. Hyostrongylus rubidus: eggs Diagnosis of this infection by finding eggs in the feces is difficult since they are similar to Oesophagostomum eggs. Cultures can be made and 3rd stage larva identified. Pathology varies from hyperemia to eroded areas of ulcers. The occurrence of clinical disease due to these infections is questionable

23. Physocephalus eggs: Thick-walled, larvated, spiruroid type eggs. ( 22 – 26u x 41 – 45 u) Ascarops eggs may be slightly smaller (34 – 39u x 15 – 17 u) but are difficult to distinguish from Physocephalus

24. Thick stomach worms: in mucosa of stomach Pathology rare, may cause gastritis with pseudomembrane formation

25. Swine stomach worms: salient points Life cycle are of trichostrongyle and spiruroid types, worms are common in pastured swine. Rx – Hyostrongylus(TBZ, levamisole, dichlorvos); spiruroids (dichlorovos).

26. Gongylonema egg( 50 – 70u x 25 – 37 u) Thick-walled, larvated egg, spiruroid type egg, larger than stomach worm eggs.

27. Gongylonema adult in tongue of pig Non-pathogenic, life cycle of spiruroid type, may also occur in mucosa of the esophagus.

28. Metastrongylus spp. Egg( 45 – 57u x 38 – 41u) Three species of lungworms commonly occur in pastured pigs, in the S.E. all produce thick-walled, larvated eggs similar in size to Ascaris eggs.

29. Metastrongylus adults in pig bronchi: A moderate amount of tissue change( and respiratory distress) have been directly associated with the worms. Worms act as vectors of swine influenza and possibly other viruses.

30. Metastrongylus: salient points Transmission is via ingestion of infected earthworms. Rx- Levamisole, fenbendazole, ivermectin.

31. Stephanurus dentatus eggs ( 100u x 60u) Rarely if ever used in diagnosis, they are found in urine

32. Stephanurus dentatus life cycle features Is direct and a long period of migration occurs, with a prepatent period of at least 6 months. Many tissues may be invaded prior to the adults locating in the renal area.

33. Stephanurus adults in urethral cyst

34. Stephanurus liver damage The predominant ( necrotic abscesses and fibrosis) produced occur in the liver during larval migrations. Other tissues may also be involved.

35. Stephanurus salient points The major problem associated with S. dentatus infections is condemnation at slaughter. Rx - Fenbendazole, ivermectin, levamisole(adults only)

36. Macrocanthorynchus hirudinaceus eggs (67 – 110u x 40 – 65u) Thick-shelled, dark brown, football-shaped

37. M. Hirudinaceus nodules on serosal surface of pig small intestines. They are due to the proboscis attachment. Generally non-pathogenic, may perforate gut

38. M. Hirudinaceus adults attached to small intestines They can be differentiated from ascarids by presence of proboscis, and wrinkled sometimes flat appearance

39. Balantidium coli cysts Common in swine rarely pathogenic, 40 – 60u organism can be recognized in cyst.

40. Balantidium coli on occasion will invade mucosa, causing ulceration and enteritis of large intestine. Tetracyclines are effective.

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