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Chapter: Medical Microbiology: An Introduction to Infectious Diseases: Tissue Nematodes

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Toxocariasis : Clinical Aspects

Larvae that reach the systemic circulation may invade any tissue of the body, where they can induce necrosis, bleeding, and the formation of eosinophilic granulomas and, subse-quently, fibrosis.

TOXOCARIASIS : CLINICAL    ASPECTS

MANIFESTATIONS

Larvae that reach the systemic circulation may invade any tissue of the body, where they can induce necrosis, bleeding, and the formation of eosinophilic granulomas and, subse-quently, fibrosis. The liver, lungs, heart, skeletal muscle, brain, and eye are involved most frequently. The severity of clinical manifestations is related to the number and location of these lesions and the degree to which the host has become sensitized to larval antigens. Children with more intense infection may have fever and an enlarged, tender liver. Those who are seriously ill may develop a skin rash, an enlarged spleen, asthma, recurrent pul-monary infiltrates and abdominal pain, sleep and behavioral changes, focal neurologic de-fects, and convulsions. Illness often persists for weeks to months, a condition frequently referred to as visceral larva migrans. Death may result from respiratory failure, cardiac arrhythmia, or brain damage. In older children and adults, systemic manifestations are uncommon. Eye invasion by larvae (ocular larva migrans) is more common. Typically, unilateral strabismus (squint) or decreased visual acuity causes the patient to consult an ophthalmologist. Examination reveals granulomatous endophthalmitis, which is usually a reaction to a larva that is already dead; it is sometimes mistaken for malignant retinoblas-toma, and an unnecessary enucleation is performed.

DIAGNOSIS

Stool examination is not helpful, because the parasite seldom reaches adulthood in humans.

Definitive diagnosis requires demonstration of the larva in a liver biopsy specimen or at autopsy. A presumptive diagnosis may be made based on the clinical picture; eosinophilic leukocytosis; elevated levels of IgE; and on elevated antibody titers to blood group antigens, particularly the group A antigen. An enzyme immunoassay (EIA) using larval antigens has been developed, providing clinicians with a reasonably sensitive (75%) and specific (90%) serologic test. A Western blot procedure is somewhat more sensitive but is not widely available. Unfortunately, many patients with related ocular infections remain seronegative; some demonstrate elevated aqueous humor titers.

 

TREATMENT AND PREVENTION

Corticosteroid treatment may be lifesaving if the patient has serious pulmonary, myocar-dial, or central nervous system involvement. Anthelmintic therapy with albendazole or mebendazole is generally administered, although the efficacy of these drugs remains un-certain. Prevention requires control of indiscriminate defecation by dogs and repeated worming of household pets. Worming must begin when the animal is 3 weeks of age and be repeated every 3 months during the first year of life and twice a year thereafter.

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