This infection is caused by ingestion of eggs from the dog and cat parasites called Toxocara canis and Toxocara cati, respectively. These worms inhabit the intestinal tract of infected dogs and cats, and their eggs appear in abundance in the feces of these animals.

However, the parasites are not infectious until three weeks after they have been excreted -- so the major risk factor for this infection is not the animal feces but the soil into which the eggs have passed. Humans may ingest the eggs by eating unwashed raw vegetables.

Young children with pica (eating inedible things such as dirt) are at highest risk, but this infection can also occur in adults. People can also become infected by eating raw liver.

After ingestion, the eggs hatch into larvae in the gastrointestinal tract and are carried into the circulation and to various tissues -- primarily the lung, liver, and eyes. The brain, heart, and other organs can also be affected.

Individuals with mild infections may have no symptoms

More serious infections are marked by fever, irritability, abdominal pain, and occasionally itchy skin lesions such as hives.

Pulmonary symptoms are common and include cough, shortness of breath, and wheezing.

If the eyes are infected, loss of vision and crossed eyes (strabismus) may occur.

Visceral larva migrans may be suspected in an individual with elevated white blood cell count (leukocytosis) and an elevated number of eosinophils (eosinophilia). An enlarged liver, rash, and lung or eye abnormalities may also be noted.

The disease may be definitively diagnosed by detection of larvae in the affected tissue. A blood test for antibodies can also be used to detect infection.

• Decreased visual acuity
• Blindness
• Respiratory distress
• Heart arrhythmias
• Encephalitis (infection of the brain)

Deworming of dogs and cats and minimizing exposure of children to areas that may be contaminated with animal feces are important preventive measures. Hand washing after handling soil is also important.