Fig. 28.1 Armillifer armillatus larvae encysted in various tissues. (A) Cross-section of two larvae lying adjacent to one another in their most common location, i.e., within the liver just beneath its capsule. (B) Tongue worm larva within the liver surrounded by a wall of fibrous tissue. (C) Larva protruding from the mesentery. (D) Larvae encysted along the peritoneal surface of the abdominal wall. X7.5. AFIP 65-6524, 55-10226-2, 65-6525 and 65-6523, respectively. (E) Section of a larval Armillifer species in a bile duct causing dilatation of the duct and fibrosis. There is an absence of spines on the cuticle; a prominent acidophilic gland is noted (arrow). X 30. (E) from Marty and Andersen in Doerr and Seifert: Tropical Pathology, 1995.)


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Epidemiology and Pathology

The Porocephalidae (which include the genera Armillifer and Porocephalus) and the Linguatulidae are families of tongue worms, belonging to the phylum Pentastomida and therefore distinct from other parasites. There are some 70 species of pentastomids, but only a few parasitize man and only two can be recognized radiologically, namely Armillifer armillatus and A. (Porocephalus) moniliformis.

The adult Armillifer species are bloodsucking, endoparasitic invertebrates with arthropod-like characteristics that live in the tracheae and lungs of snakes and reptiles. The adult is whitish or yellow, and translucent with an elongated cylindrical vermiform body, tapering to a blunt tail. The body is extended with prominent bracelet-like rings or annuli that give the worm a screw-like appearance. The adult male measures 30 to 45 mm in length by 3 to 4 mm in width and has 17 to 24 rings, whereas the female is 90 to 120 mm long by 5 to 9 mm wide and has 18 to 22 rings. Both sexes of Armillifer (Porocephalus) moniliformis are more slender and have more rings or annuli (26 or greater) than A. armillatus. The nymphs of both species are coiled within their cysts in a flat spiral and resemble the adults in shape and structure, although being much smaller.

The usual intermediate hosts for the Armillifer species are rats, monkeys and other wild and domestic animals which may be infected by coming into contact with the saliva or excreta of an infected snake. Humans become infected either by ingesting ova in contaminated food or water or by ingesting larvae and acting as intermediate hosts; in certain African tribes, they may also become infected by eating uncooked infected snakes. Once the ova reach the intestinal tract of a suitable intermediate host (including humans), a viable embryo soon emerges from its egg to become a first-stage larva. These larvae penetrate through the gut wall and migrate for several days along the peritoneum and pleura before becoming encysted in various tissues such as the liver, spleen, mesentery and lungs (Fig. 28.1). This primary larval stage of pentastomiasis causes little or no significant clinical reaction. However, the developing cysts may increase markedly in size and in volume and occasionally cause symptoms by pressure upon critical structures such as bile ducts or bronchi, leading to obstruction and infection. A granulomatous reaction can develop in association with larvae in the liver which are usually related to tributaries of the hepatic veins. In Ibadan in Nigeria, Smith et al (1975) found pentastomiasis to be the third most common cause of hepatic fibrosis after tuberculosis and schistosomiasis.

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