# Blastocystis in a Liver Abscess: An Unusual Extraintestinal Location

## TL;DR

A 43-year-old woman had a liver abscess caused by Blastocystis, a gut protist, suggesting it can spread beyond the intestines.

## Contribution

Demonstrates Blastocystis subtype ST1 in a liver abscess, supporting extraintestinal infection via gut microbiota translocation.

## Key findings

- Blastocystis ST1 was identified in liver abscess fluid and cultured in vitro.
- Gut bacteria like Escherichia coli and Bacteroides fragilis were also detected in the abscess.
- The infection likely originated from gut microbiota entering the portal circulation.

## Abstract

Blastocystis is a common anaerobic protist of uncertain pathogenicity that inhabits the human intestine. Rare cases reported in the literature suggest possible extraintestinal dissemination by unclear mechanisms. We followed a 43‐year‐old Peruvian woman presenting with low‐grade fever and gastrointestinal symptoms who was diagnosed with a liver abscess by ultrasound and CT imaging. Identification of the causative agents was achieved through a combination of mass spectrometry, molecular methods (PCR and Sanger sequencing) and culture‐based methods in blood, tissue and faecal samples. We detected gut‐associated aerobic and anaerobic bacteria, including Escherichia coli, Eikenella corrodens and Bacteroides fragilis. Active forms of Blastocystis subtype ST1 were identified in the liver abscess fluid and successfully cultured in vitro. These findings suggest translocation of gut microbiota into the portal circulation as the underlying route of infection. Blastocystis can act as an opportunistic invasive microorganism in locations other than the intestinal tract.