Diagnosis: Massive human pentastomiasis.
Pentastomiasis is a zoonotic parasitic disease first described by Pruner in 1847 (cited in [1]). The causative organisms are pentastomes (pentastomids), so called because of the presence of 2 pairs of anterior hooks and a mouth that give the appearance of 5 openings. Pentastomes are annulated but nonsegmented vermiform blood-sucking endoparasites. They are probably best classified as a separate phylum, the Pentastomida, with characteristics of both arthropods and annelids. Of medical interest are 2 families of pentastomes, Linguatulidae and Porocephalidae, of which only 2 species, Armillifer (Porocephalus) armillatus and Linguatula serrata, account for >99% of human infections [2]. The adult stages of Armillifer and Linguatula are parasites of the respiratory tract of snakes (Pytho and Bitis species) and carnivorous mammals (e.g., dogs), respectively. The primary larvae develop into encysted nymphs in tissues of various intermediate hosts, especially rodents (for Armillifer) and sheep and goats (for Linguatula).
Pentastomiasis has been reported most commonly in Africa and Asia, and cases in Europe and the Americas are much more occasional. The infection is common in central Africa and Malaysia, where the prevalences were found to be 7.8%–22.5% and 45.5%, respectively, in an autopsy study series [3]. In Mali, specific antibodies were detected in 2% of individuals in a serological study [4].
A. armillatus infects humans as a secondary host. A person becomes infected accidentally by ingesting eggs from soil, vegetation, or water contaminated with feces or secretions from the respiratory tracts of snakes. Direct contamination can also occur from handling or consuming inadequately cooked snakes, resulting in massive infection, as in the case we describe. The majority of infections are asymptomatic and manifest as incidental radiological, surgical, or autopsy findings. However, symptomatic patients who have a history of chronic abdominal pain [5, 6] or present with an acute abdominal emergency [3, 7] have been reported. Two cases of generalized and lethal pentastomiasis in 5-year-old girls have been reported [8, 9]. Ocular involvement has been also occasionally reported and is probably due to direct contact with eggs [10]. Complications are mainly associated with live unencapsulated larval stages [3].
Encapsulated nymphs have characteristic features visible on plain abdominal radiographs. Calcified larvae appear as multiple (generally 1–12) dense opacities, 0.5–1 cm in diameter, that are circular, crescent-shaped, or C-shaped and have been described as looking like broken rings, or commas, cashew nuts, or horseshoes [3, 5, 7]. On side view, the opacities appear as round-ended rods, an appearance that is less suggestive (figure 1).
Abdominal radiograph demonstrating characteristic C-shaped and rod-like aspects of the calcified nymphs (hollow arrow and white arrow, respectively).
Abdominal radiograph demonstrating characteristic C-shaped and rod-like aspects of the calcified nymphs (hollow arrow and white arrow, respectively).
Larval aspects have been rarely shown on CT scans [6]. CT scanning can contribute greatly to the diagnosis by showing precisely the shape and location of the parasites. The nymphs locate preferentially in the serous membranes, most often the mesentery and the hepatic and intestinal visceral peritoneum, the intestinal wall, the liver and splenic capsules, and the liver parenchyma (figure 2). Thoracic localizations are less common, involving the pericardium and the lung parenchyma (figure 3).
CT scan at the abdominal level demonstrating calcified larvae in the mesentera and the peritoneum (white arrow), the liver and splenic capsules (hollow arrows), and the liver parenchyma.
CT scan at the abdominal level demonstrating calcified larvae in the mesentera and the peritoneum (white arrow), the liver and splenic capsules (hollow arrows), and the liver parenchyma.
CT scan at the thoracoabdominal level demonstrating calcified larvae in the pericardium (white arrows) the left lung parenchyma (hollow arrows), the liver, and the posterior peritoneum.
CT scan at the thoracoabdominal level demonstrating calcified larvae in the pericardium (white arrows) the left lung parenchyma (hollow arrows), the liver, and the posterior peritoneum.
In most cases, the characteristic shape and localizations of the calcified nymphs are easily differentiated from multiple calcifications of other origins, such as those characteristic of cysticercosis, which are elliptical in shape and involve strictly the muscular tissues, or those characteristic of massive histoplasmosis, which are heterogeneous in shape and situated in the liver or spleen parenchyma. The diagnosis can be confirmed by surgery (figure 4).
Picture and diagram of the pentastome parasite in a liver biopsy specimen (hematoxylin-eosin stain).
Picture and diagram of the pentastome parasite in a liver biopsy specimen (hematoxylin-eosin stain).
L. serrata may infect humans at its larval stage, as does A. armillatus, or cause a self-limited nasopharyngitis—the halzoun or marrara syndrome—with the human acting as an accidental definitive host [10]. Treatment is not usually necessary, because most cases are discovered incidentally, from radiological findings, as in the case we describe. No specific treatment is available; thus free or encysted larvae in symptomatic patients should be removed surgically. Prophylaxis is based mainly on adequate cooking and appropriate handling of snakes.
Acknowledgments
Potential conflict of interest. All authors: No conflict.
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