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Laboratory Diagnosis

The diagnosis of ascariasis depends on the identification of the adult worms passed through the rectum or from some other body orifice, or by identifying the eggs of A. lumbricoides in the stool, vomitus, sputum, or small bowel aspirate. Occasionally eggs, larvae, or adult worms may be identified in tissue sections. The radiological appearance of the worms in the gastrointestinal or biliary tracts is highly characteristic. Diagnosis during the stage of larval migration is difficult, although occasionally larvae may be found in the sputum or gastric contents. Once the fertile females within the gut begin to release eggs, the diagnosis of ascariasis can usually be made by direct fecal smears. However, concentration techniques using centrifugation (eg, formalin-ethyl acetate method) may facilitate diagnosis.

An increased number of circulating eosinophils is often present but less marked than in other parasitic infections in which migrating larvae or eggs deposited in body tissues remain alive for a long period of time. The eosinophil count is highest during the stage of larval migration, about the time the pulmonary symptoms begin to subside. At this stage, an eosinophilia of 30% to 50% may be present for a short period. However, when mature worms develop (intestinal ascariasis), eosinophilia usually ranges between 5% and 12% and rarely above 25%.

There are several serologic tests which can detect antibodies to Ascaris, but as yet there is no specific immunodiagnostic test, since antibodies to Ascaris often cross-react with antigens from other helminths. Serology is therefore not often used because of cross-reactivity.

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