| Adults of the large roundworm,
Ascaris
suum
, are found principally in the small intestine but may migrate into the stomach or bile ducts. They are ~30 cm long, whitish, and quite thick. Large numbers of eggs are produced (as many as 250,000/day); they can develop to the infective stage (containing the L3 larva) in 2-3 wk in warm conditions. The eggs are resistant to chemical agents, but conditions with low humidity, heat, or direct sunlight may reduce their survival significantly. When the
eggs are ingested, the larvae hatch in the intestine, penetrate the large intestinal wall, and enter the portal circulation. After a period in the liver, they are carried by the circulation to the lungs, where they pass through the capillaries into the alveolar spaces. About 9-10 days after ingestion, the larvae pass up the bronchial tree to return to the GI tract. On arrival in the small intestine the majority of the larvae are expelled; remaining larvae develop into mature adult
worms. The first eggs are passed 1½-2½ mo after infection.
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| Clinical Findings: |
| Adult worms may significantly reduce the growth rate of young pigs; if sufficiently numerous, they may cause mechanical obstruction of the intestine, or migrate into and occlude the bile ducts, producing icterus. Migration of larvae through the liver causes hemorrhage and fibrosis that appears as “white spots” under the capsule and leads to condemnation of the liver at slaughter. In heavy infections, the larvae can cause pulmonary edema and consolidation as well as exacerbate
swine influenza and endemic pneumonia. Affected pigs show abdominal breathing, commonly referred to as “thumps.” In addition to the respiratory signs, marked unthriftiness and weight loss are seen. Permanent stunting may result in pigs up to 4-5 mo old. The infection generally induces the development of resistance to reinfection.
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| Diagnosis: |
| During the patent period, diagnosis can be made by demonstrating the typical eggs (golden brown, thick pitted outer wall, 50-70 × 40-60 µm) in the feces. However, many young pigs show signs (especially respiratory) during the prepatent period. A presumptive diagnosis can be made based on history and signs and confirmed by demonstrating immature worms on necropsy. In acute cases in which no worms are found in the intestine, it may be possible to recover larvae from affected lung
tissue. |
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| Treatment: |
| Supportive therapy, including treatment for secondary bacterial invaders, may be necessary during the respiratory phase of infection. Many drugs have been used to remove adult ascarids. Piperazine preparations have low toxicity and are moderately priced. The benzimidazoles and probenzimidazoles, dichlorvos, ivermectin, levamisole, and pyrantel are effective and have a broader spectrum of activity than piperazine. Hygromycin is active against ascarids when administered as a
low-level additive to the feed. Less information is available concerning the control of migratory stages; pyrantel and fenbendazole show activity. |
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