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Laboratory Diagnosis

The diagnosis of anisakiasis can be established when the worm (larva) is obtained from the patient's vomitus or stool (usually an unrewarding experience), or during endoscopy or surgery. For both gastric and intestinal anisakiasis the procedure of choice is usually endoscopy since it provides easy recognition of a larva burrowing into, or attached to, the mucous membrane of the stomach or intestine (Fig. 11.2A). The larva can be extracted by biopsy forceps and the species identified (Fig. 11.2B). An experienced physician can often differentiate Anisakis from Pseuoterranova species via the endoscope, since the former has the appearance of a thin white string, whereas Pseudoterranova is broader and yellowish-brown. A biopsy should be undertaken if endoscopy shows nonspecific findings of localized edema or "tumor formation", erosion or bleeding, and the biopsy material divided for parasitology and histology examinations.


Fig. 11.2 (A) Endoscopic view of a live Anisakis, the head of which is still attached to the gastric mucosa (arrow) of a Japanese patient. (B) The worm is being withdrawn from the stomach by forceps. (Courtesy of Dr. Yoshihiro Hiramatsu, Tokyo, Japan).

A leukocytosis is usually present if complications such as ileus, perforation or peritonitis develop. Peripheral eosinophilia has been reported in 4 to 41% of patients and is usually commoner the more protracted the disease; it is thus of greater value in the more chronic intestinal form of anisakiasis than in the more acute gastric form. Occult blood is frequently present in the stool.

There have been many attempts to develop a serodiagnostic assay for anisakiasis, but only in recent years have sensitive methods for the detection of parasite-specific IgG and IgE antibodies been established. The specificity of immunological tests may be increased by the characterization of excretory-secretory antigens of the larvae and the use of monoclonal antibodies in an enzyme-linked immunosorbent assay (ELISA). Parasite-specific antibodies can be detected within 1 to 60 days after onset of symptoms.

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