Histopathological Features of the Colon in Chronic Strongyloidiasis: A Case Series

Strongyloidiasis, which is caused by Strongyloides stercoralis (a nematode), is a prevalent human intestinal parasitic disease, particularly in tropical and subtropical regions. Okinawa Prefecture exhibits the highest prevalence of strongyloidiasis in Japan. This nematode has the unique ability to replicate for years within a human host with minimal or no symptoms, a phenomenon known as autoinfection. Patients with Strongyloides stercoralis autoinfection are often asymptomatic or experience uncomplicated infections, and, hence, are considered to have chronic strongyloidiasis. In this study, we retrospectively investigated the characteristic colonoscopic and histopathological findings of the colon in patients with chronic strongyloidiasis. From 2004 to 2023, 22 almost asymptomatic patients underwent colonoscopy as part of routine health check-ups at one of three centers in Okinawa, Japan. The subjects' ages ranged from 53 to 87 years. The male-to-female ratio was 17:5. Colonoscopy showed yellowish-white nodules on the cecum and the proximal ascending colon. Biopsy specimens revealed filariform Strongyloides larvae with small, dense infiltrations of eosinophils in the lamina propria. The findings presented in this study are useful for diagnosing chronic strongyloidiasis and suggest that the re-invasion sites of filariform larvae may be located in the cecum and proximal ascending colon.