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Toxocariasis is human infection with nematode ascarid larvae that ordinarily infect animals. Symptoms are fever, anorexia, hepatosplenomegaly, rash, pneumonitis, asthma, or visual impairment. Diagnosis is by enzyme immunoassay. Treatment is with albendazole or mebendazole. Corticosteroids may be added for severe symptoms or eye involvement.
Pathophysiology
The eggs of Toxocara canis, T. cati, and other animal ascarid helminths mature in soil and infect dogs, cats, and other animals. Humans may accidentally ingest eggs in soil contaminated by stool from infected animals or may ingest infected transfer hosts (eg, rabbits). The eggs hatch in the human intestine. Larvae penetrate the bowel wall and may migrate through the liver, lungs, CNS, eyes, or other tissues. Tissue damage is caused by focal eosinophilic granulomatous reactions to the migrating larvae. The larvae usually do not complete their development in the human body but can remain alive for many months.
Symptoms and Signs
Visceral larva migrans (VLM)
This syndrome consists of fever, anorexia, hepatosplenomegaly, rash, pneumonitis, and asthmatic symptoms, depending on the affected organs.
VLM occurs mostly in 2- to 5-yr-old children with a history of geophagia. The syndrome is self-limiting in 6 to 18 mo if egg intake ceases. Deaths due to invasion of the brain or heart occur rarely.
Ocular larva migrans (OLM)
This syndrome, also called ocular toxocariasis, usually has no or very mild systemic manifestations. OLM lesions consist mostly of granulomatous reactions to a larva in the retina; the larva may cause visual impairment.
OLM occurs in older children and less commonly in young adults. The lesion may be confused with retinoblastoma or other intraocular tumors.
Diagnosis
Diagnosis is based on clinical, epidemiologic, and serologic findings. Enzyme immunoassay (EIA) is currently recommended. Isoagglutinins are frequently elevated, but this finding is nonspecific. Hyperglobulinemia, leukocytosis, and marked eosinophilia are common.
Biopsies of the liver or other affected organs may show eosinophilic granulomatous reactions, but larvae are difficult to find in tissue sections and biopsies are low yield. Stool examinations are worthless. OLM should be distinguished from retinoblastoma to prevent unnecessary surgical enucleation of the eye.
Treatment
Mebendazole 100 to 200 mg po bid for 5 days or albendazole 400 mg po bid for 5 days is often used, but the optimal duration of therapy has not been determined.
Antihistamines may suffice for mild symptoms. Corticosteroids (prednisone 20 to 40 mg po once/day) are indicated for patients with severe symptoms. Corticosteroids, both local and oral, are also indicated for acute OLM.
Laser photocoagulation has been used to kill larvae in the retina.
Prevention
Infection with T. canis in puppies is common in the US; infection with T. cati in cats is less common. Both animals should be dewormed regularly. Contact with dirt or sand contaminated with animal feces should be minimized. Sandboxes should be covered.
Baylisascariasis
Baylisascariasis is infection with the raccoon ascarid, Baylisascaris procyonis, which may cause fatal CNS infection in humans.
Infection usually occurs in children who play in dirt or with articles contaminated with raccoon feces. It occurs in the US, particularly in the Middle Atlantic, Midwest, and Northeast. Although baylisascariasis is rare in people, it is of concern because a large number of raccoons live near humans and the infection rate of B. procyonis in these animals is high.
Migration of the larvae through a wide variety of tissues (liver, heart, lungs, brain, eyes) results in VLM and OLM syndromes, similar to those due to toxocariasis. However, in contrast to Toxocara larvae, Baylisascaris larvae continue to grow to a large size (up to 24 cm for females and 12 cm for males) within the CNS and cause eosinophilic meningoencephalitis. Tissue damage and symptoms and signs of baylisascariasis are often severe because Baylisascaris larvae continue to grow, tend to wander widely, and do not readily die.
Diagnosis is difficult because serologic tests are not widely available. Viewing a larva during ocular examination is often a clue.
Treatment is similar to that of other causes of VLM and OLM.
Last full review/revision December 2009 by Richard D. Pearson, MD
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