Nematode Zoonoses - ASCARIASIS

(Roundworm infection, ascaridiasis) A common, but usually mild, roundworm infection of both humans and animals, occurring worldwide. There is doubt whether the worms cross between species. The causative agent in humans is usually Ascaris lumbricoides. Ascaris suum in pigs is considered occasionally a zoonotic infection (Nematoda). There is no vaccine.

RESERVOIR AND MODE OF TRANSMISSION:

A. lumbricoides has its reservoir in humans and in contaminated soil. A. suum occurs in pigs. Eggs are passed in feces and become infective after two weeks. Infection is by the ingestion of eggs in soil or undercooked food. Eggs hatch in the gut, penetrate its wall and reach the lungs via the bloodstream. Larvae develop in the lungs, ascend the trachea and are swallowed and mature in the gut. Egg-laying begins 45-60 days after initial infection.

INCUBATION PERIOD:

Humans. About two months. Animals. Development of A. suum in the pig is said to be quicker than in the human.

CLINICAL FEATURES:

Humans. The condition is usually asymptomatic but there may be fever with asthma, spasmodic coughing and possibly pneumonitis. Abdominal pain, and even bowel or bile duct obstruction, is possible. Occasionally migrating larvae cause symptoms referable to the brain, eyes, kidneys and liver.
Animals. Migrating larvae cause irregular breathing and coughing. Heavy infection gives abdominal pain with diarrhoea. Suckling pigs are most affected.

PATHOLOGY:

Humans. Eosinophilia and pulmonary eosinophilic infiltration occur. Liver abscesses and cholangitis are sometimes seen.
Animals. Larvae migrating through the lung cause pneumonia. Worms in the intestine give enteritis.

DIAGNOSIS:

Humans. Identify eggs or adult worms in feces. Larvae in sputum or gastric washings are diagnostic.
Animals. Examine feces for eggs, or monitor worms passed rectally or via mouth and nose. An egg count of more than 1000/g of feces indicates clinical disease.

PROGNOSIS:

Humans. The condition is rarely fatal. Aberrant larvae in brain, eyes and kidney can give severe symptoms.
Animals. Rarely fatal.

PREVENTION:

Humans. Sanitary disposal of feces coupled with good personal and food hygiene are essential.
Animals. Worm and wash sows before farrowing. Rear pigs on concrete or avoid close confinement on soil.

TREATMENT:

Humans and animals. Pyrantel pamoate is the treatment of choice. Stools should be rechecked at 2 weeks and patients retreated until all ascarids are removed.