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Chapter 28

Pentastomiasis (Armillifer Infection)

Pentastomiasis, also known as porocephalosis or tongue worm infestation, is yet another reason to avoid snakes! The parasites responsible for this bizarre, but usually innocuous, disease look like worms but are actually arthropods and belong to the large group of pentastomids that normally inhabit the respiratory tracts of snakes and reptiles and only occasionally infect humans. Few patients are concerned about the parasite, being far more interested in the snake. Pentastomids have been associated with reptiles for many eons and it is probable that carnivorous dinosaurs, the great land reptiles of the Mesozoic period, harbored pentastomids and that the present parasites are descendants of these remote ancestors.

The larvae, nymphs and adults of two genera, Linguatula and Armillifer, may infect man. Ingested infective larvae of the Linguatula species migrate to the nasal passages of humans serving as unwitting hosts, causing nasopharyngeal linguatulosis, which may manifest itself as nasopharyngael obstruction or suffocation (known as Halzoun syndrome or marrara in Southwest Asia where it most commonly occurs). While important clinically at times, this infection with Linguatula has no radiological significance and will not be discussed further.

The invading larvae of Armillifer become encapsulated nymphs in the liver, mesentery and other deep organs and tissues and cause visceral pentastomiasis, which is only occasionally symptomatic. Two species of Armillifer can be identified radiologically in man: Armillifer armillatus, the calcified nymphs of which are found most commonly in West Africans in whom the infestation rate may be as high as 23% and the radiological incidence up to 1.4%; and Armillifer (Porocephalus) moniliformis, which occurs throughout much of South and East Asia and, in a 1969 report from Prathap et al, was found at autopsy in 45% of Malaysian aborigines.

Synonyms Porocephalosis. Porocephaliasis. Linguatuliasis. Linguatulosis. Tongue worm infection or infestation. Armillifer infection. Halzoun syndrome. Marrara.

Definition Human pentastomiasis is infection with Armillifer armillatus, Armillifer (Porocephalus) moniliformis, Armillifer grandis, Porocephalus crotali, or Linguatula serrata.

Geographic Distribution

The pentastomids are widely distributed. The adult Armillifer armillatus lives within the tracheae and bronchi of royal pythons, puff adders and cobras, and is found most commonly in West and Central Africa, especially Nigeria and the Democratic Republic of Congo, and less often in East and southern Africa. Pentastomiasis has been identified at autopsy in 22.5% of patients from the Democratic Republic of Congo, in 8% from Cameroons and in 5% from West Africa. Armillifer (Porocephalus) moniliformis occurs in pythons and other snakes of India, Malaysia, Southeast Asia, China, Indonesia and the Philippines. Armillifer grandis is a rare Central African species. Linguatula serrata is the second commonest cause of human pentastomid infection, but this parasite has no radiological significance. The adults of this species live in the lungs of snakes and the nasopharynx of carnivores of the feline and canine families, and are found in many areas of the world, particularly in Europe, the Near and Middle East, and Brazil. Porocephalus crotali, which may rarely infect man, occurs in rattlesnakes in North and South America but also has no radiological significance.

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Copyright: Palmer and Reeder

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