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Epidemiology and Pathology

Normally the fully developed third stage larva has reached a dead end in man and remains encysted. Within 2 years it dies, sometimes provoking a localized inflammation and becoming absorbed, or calcifying to give a characteristic radiographic appearance. Occasionally, however, these third-stage larvae escape from their cysts and enter the peritoneal cavity. Thus both of the free larval stages show an inclination for migration: the first-stage larvae (the stage prior to encystment) and the third-stage infective larvae which have emerged from their cysts. The latter seldom migrate extensively in man and thus rarely produce extensive tissue damage or clinical symptoms except in heavy infections. In one series of 32 autopsies, the distribution of 269 larvae (all but 5 of which were encysted) was found to be: subcapsular and parenchymal portions of the liver (54%), mesentery and mesenteric ganglia (20%), intestinal wall (10%), parietal peritoneum of the spleen and kidney (6%), the greater omentum (6%) and the lung (1.4%).

When the intermediate host (a small animal or, rarely, man) is eaten by a snake (the definitive host), the encysted larvae are released into the intestine of the snake and develop into adult parasites, thus reinstituting the life cycle. Occasionally man acts like the definitive (reptile) host and ingests mature larvae which, in the case of Linguatula, try to complete their life cycle by migrating to the nasopharyngeal region, causing the Halzoun syndrome.

Laboratory Diagnosis

The diagnosis of pentastomiasis depends on either the identification of live nymphs or the typical radiological appearance of the calcified dead larvae. There are no satisfactory laboratory tests. A mild eosinophilia can occur, but is nonspecific.

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Copyright: Palmer and Reeder

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