Definition
Ascariasis is the infestation of swine by the roundworm, Ascaris suum, which can cause pneumonia, hepatitis, and ill thrift.
Occurrence
Ascariasis occurs worldwide in countries that raise significant numbers of swine. All ages are affected but Ascariasis is more severe in young, growing pigs. It is the most prevalent and most economically important internal parasite of swine.
Migration of ascarid larvae occurs in several other animals, including man, but larvae usually do not develop to the adult stage in the intestine of these species. Migrating larvae occasionally infect lambs and calves and cause heavy losses from pulmonary lesions.
Life cycle of Ascarid.
When the eggs are ingested, the larvae hatch in the intestine, penetrate the wall, and enter the portal circulation. After a short period in the liver, they are carried by the circulation to the lungs, where they pass through the capillaries into the alveolar spaces. Approximately 9–10 days after ingestion, the larvae pass up the bronchial tree, are swallowed, and return to the small intestine by ~10–15 days after infection, where they mature into adult worms. The first eggs are passed ~6–7 weeks after infection. The lifespan is ~6–9 months. Earthworms and dung beetles can serve as paratenic hosts.
Etiology
Mature ascarids are 15-40 cm long, thick bodied, round worms. A mature ascarid (prepatent period of seven to eight weeks) can lay almost two million eggs per day. Adults live in a pig for about six months before spontaneous expulsion begins but may survive a year or longer. Heavy infections can result in hundreds of ascarids in the intestine of a single pig.
Ascarid eggs are thick shelled, yellowish brown, almost spherical, 50-80 by 40-60 µm, and are coated with a sticky proteinaceous cover. The eggs are quite resistant to environmental degradation and disinfectants but can be destroyed by intensive steam cleaning or prolonged exposure to full sunlight.
Clinical signs
Signs in young, growing pigs include unthriftiness, failure to gain weight, rough hair coat, pendulous abdomen, chronic paroxysmal coughing and occasionally, abdominal expiratory dyspnea (“thumping”).
Severe, sometimes fatal, the respiratory disease may result in 7-14 days after naïve pigs (feeder pigs or breeding stock previously unexposed) are placed in facilities heavily contaminated with ascarid eggs. Affected pigs are afebrile, “thump,” are gaunt, and are often misdiagnosed as having bacterial or viral pneumonia. Other effects in heavily exposed gilts include delayed estrus, poor conception rate, pneumonia or death.
Lesions
By 5-14 days after ingestion of infective eggs, there are small hemorrhages on and throughout the lungs. Larvae and inflammatory exudate obstruct smaller airways (verminous pneumonia). Often, there is secondary suppurative bronchopneumonia. Pneumonia may be accompanied by emphysema that interferes with the collapse of the lungs. Scarring in the liver first appears by 7-14 days after exposure as scattered, gray to white “milk spots” (0.2-1 cm) visible under the liver capsule that later expands, coalesces and can eventually resolve. In heavy infections, diffuse fibrosis may affect the entire liver and lead to its condemnation at slaughter. Minor areas of scarring can be repaired in 30 to 60 days, making diagnostic reliability of detecting an absence of liver lesions at slaughter dubious.
Diagnosis
Diagnosis of chronic infestation (more than two months) can often be made by identifying eggs using fecal flotation examinations or by finding grossly visible ascarids in the small intestine. Since ascarids have some mobility, they sometimes can be found in the stomach or in the major bile and pancreatic ducts at necropsy. Obstruction of the bile duct sometimes leads to marked generalized icterus. Ascarids may not be present in animals recently “dewormed” but scarring in the liver or hemorrhages in the lung may still be apparent.
Diagnosis of acute infestations (less than two months) requires postmortem examination of a few typical pigs that have died or been sacrificed. Fecal flotations are not reliable during the first 6-8 weeks following infestation (prepatent period). Postmortem examination also permits the evaluation of concurrent diseases, including other sources of parasitism or causes of pneumonia. Diagnosis of early infestations is by observation of typical liver and lung lesions with confirmation by histopathology.
Prevention:
- Deworming the sows during gestation (usually about a week before farrowing); washing the sows to remove parasite eggs prior to putting them in sanitized farrowing crates; early weaning of two to four week old pigs (before ascarid eggs have become infective); and using all in/all out production systems with thorough cleaning between groups.
Treatment:
+ Albendazole 10% 1ml/12 kg body weight.
+ Vimectin premix 1g/30 kg body weight, feed continuously for 7 days.
+ Vimectin 0,3% inject 1ml/10 kg body weight.
