Diagnosis of human visceral pentastomiasis

Abstract

Visceral pentastomiasis in humans is caused by the larval stages (nymphs) of the arthropod-related tongue worms Linguatula serrata, Armillifer armillatus, A. moniliformis, A. grandis, and Porocephalus crotali. The majority of cases has been reported from Africa, Malaysia, and the Middle East, where visceral pentastomiasis may be an incidental finding in autopsies, and less often from China and Latin America. In Europe and North America, the disease is only rarely encountered in immigrants and long-term travelers, and the parasitic lesions may be confused with malignancies, leading to a delay in the correct diagnosis. Since clinical symptoms are variable and serological tests are not readily available, the diagnosis often relies on histopathological examinations. This laboratory symposium focuses on the diagnosis of this unusual parasitic disease and presents its risk factors and epidemiology.

Figure 1. Nymphal and adult pentastomes.

(A) Excised nodule on the pleural surface of the lung showing nymphal L. serrata. (B) Coiled nymphs of Armillifer sp. in simian omentum. (C) Adult female L. serrata. (D) Adult male (small) and female (large) of Armillifer sp. (E) Adult P. crotali in snake lung. (F) Anterior part of Armillifer with central mouth and four oral hooks.

Figure 2. Radiograph of the pelvis from female patient with chronic lower abdominal pain.

Calcified Armillifer nymphs (arrows) are shown in front of the iliac bones of a Nigerian patient. (Radiograph by courtesy of Klaus-J. Volkmer, Germany)

Figure 3. Sections through vital, well-preserved pentastomid nymphs.

(A) Longitudinal section through coiled Armillifer sp. in the omentum with one oral hook visible (arrow). The cuticle shows sections of the prominent spirals (arrowhead). Note the shed cuticle (exuvia, ex) of the previous developmental stage in close contact to the parasite inside the capsule (ag, acidophilic glands). (B) Cross section of Armillifer sp. in the lung showing primordial genital tract (gt), red acidophilic (ag) and blue subcuticular glands (sg), intestine (in), muscles (mu), and exuvia (ex). There is not much host reaction. (C) Anterior portion of L. serrata nymph in a lymph node showing two pairs of oral hooks (arrows), intestine (in), and acidophilic glands (ag). (D) Part of a degenerated nymph showing cuticular annuli, which are responsible for the serrated aspect of this species. On each annulus, a spine is visible (arrow). (E) Close-up of row of spines (arrow). (F) Close-up of individual cuticular spine with separate inner structure (arrowhead). Scale bars: (A–C) = 500 µm; (D, E) = 40 µm; (F) = 20 µm. Hematoxylin and eosin (A, C); trichrome stain (all others).

Figure 4. Body wall with cuticular openings and oral hooks of pentastome nymphs.

(A–D) Armillifer nymphs with sclerotized openings (arrows) in the cuticle (cu) and the exuvia (ex). Subcuticular gland cells (sg) are also visible. (C) Cross section of two sclerotized openings. (E) Oral hooks (arrows) and spines (arrowhead) of L. serrata. (F) Anterior part of A. armillatus showing two oral hooks (arrows) and acidophilic glands (ag). (G) Degenerated L. serrata nymph with typical oral hook (arrow) and cuticle (cu) still visible. (H) Close-up of the base of an individual hook (arrows) of A. armillatus with fascicles of striated muscles (mu) inserting at the base. (I) Detail of subcuticular striated muscles. Scale bars: (B) = 10 µm; all others = 40 µm. Hematoxylin and eosin (E); trichrome stain (all others).

Figure 5. Different types of tissue reactions of human patients to vital, degenerated, and nearly absorbed pentastome nymphs.

(A) Viable nymph (ny) of A. armillatus with thin fibrous capsule in the lung. (B) Three cross sections of one viable A. armillatus in the intestinal wall with very little cellular reaction. (C) Body wall of a well-preserved vital nymph (ny) of A. armillatus in the liver with exuvia (arrow), a thick fibrous capsule, and moderate infiltration of the adjacent liver tissue. (D) Dead and degenerated A. armillatus in a lymph node with a thick fibrous capsule. (E) Linguatula nodule with target-like appearance in human lung. In the center of the nodule, a dead degenerated nymph (ny) is visible. Due to the coiled shape of the nymph, two adjacent fibrous rings are discernable on this section. (F) Granulomatous scar with central amorphous mass in the lung. Remnants of the cuticle (arrow) of L. serrata are still left. Scale bars: (C) = 100 mm; all others = 500 µm. Hematoxylin and eosin (B); trichrome stain (all others).