Direct parasitologial diagnosis of infection with Hysterothylacium aduncum in a patient with epigastralgia

Diagnóstico parasitológico directo de infección por Hysterothylacium aduncum en un caso de epigastralgia

Yolanda González-Amores¹, Encarnación Clavijo-Frutos², Carmen Salas-Casanova³ and Guillermo Alcain-Martínez¹

¹ Department of Digestive Diseases and ² Department of Microbiology and Parasitology. Hospital Universitario Virgen de la Victoria. Málaga, Spain.
³ Department of Parasitology. School of Biology. Universidad de Málaga. Málaga, Spain

Case report

A patient with no relevant history presented with epigastralgia for the last 4 hours. A lab workup showed no significant findings. Abdominal CT revealed gastric wall thickening with increased contrast uptake and adipose tissue rarefaction (Fig. 1). A gastroscopy was performed 12 hours after admission, which revealed an edematous, erythematous antral mucosa with 4 whitish, worm-like structures about 15 mm in length attached to it by one end. The diagnosis was reached by direct endoscopic observation, light microscopy, and scanning electron microscopy - no serology testing was needed (Fig. 2). The patient initially denied having eaten raw fish, only to later confirm its ingestion after endoscopy. Following parasite removal the patient remained asymptomatic and treatment with albendazole was initiated.

Discussion

Direct observation allowed parasite identification as third-stage (L3) larvae of Hysterothylacium aduncum, an ascaroid nematode belonging to the Anisakidae family (1). Hysterothylacium aduncum is an unusual parasite - it has only been described as the causal agent of at least one case of non-invasive anisakiasis (2). Body size is consistent for this species' L3 stage (Figs. 3 and 4). Manifestations result from local damage (epigastralgia, vomiting, obstruction, diarrhea, ulceration, bleeding) and hypersensitivity reactions (urticaria, angioedema, shock) (3). A definitive diagnosis may only be reached by direct parasite visualization (4). Diagnosis is challenging and relies on clinical suspicion, findings such as eosinophilia, recent raw fish ingestion, and both direct (endoscopy) and indirect (serology) testing.

The prevalence of anisakiasis has been on the rise worldwide for the last few years (5), which may result from improved diagnostic technique resolution, increased interest in dishes consisting of raw fish, and coexistence of sea mammals acting as reservoirs in fishing areas.

References

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