Intestinal Parasites and Infestation

Michael P. Federle, MD, FACR

R. Brooke Jeffrey, MD

Key Facts

Terminology

Enteric infection with roundworm Ascaris lumbricoides (ascariasis)
Enteric protozoal infection with Giardia lamblia (giardiasis) or with Entamoeba histolytica (amebiasis)

Imaging

Best diagnostic clue
- Ascariasis: Linear filling defect on small bowel follow through (SBFT)
- Giardiasis: Thickened duodenal/jejunal folds on SBFT
- Amebiasis: Diffuse ulcerating colitis, right lobe liver abscess on CECT
Location
- Small bowel (SB), colon, common bile duct (CBD) or pancreatic duct (ascariasis); duodenum, jejunum (giardiasis); colon, liver (amebiasis)
Best imaging tool
- SBFT (ascariasis and giardiasis); barium enema, CECT (amebiasis)

Top Differential Diagnoses

Crohn disease
Ulcerative colitis
Pseudomembranous colitis

Clinical Issues

Ascariasis infests 25% of world population
Giardiasis most common protozoal disease in USA
Amebiasis infests 10% of world population

Diagnostic Checklist

Consider Crohn disease, ulcerative colitis

(Left) Axial CECT with intravenous and oral contrast in a 19-year-old woman from Mexico status post motor vehicle crash reveals linear filling defects

in the proximal small bowel. These defects represent the roundworm Ascaris lumbricoides. (Right) Anteroposterior view of a small bowel follow through demonstrates thickened folds in the proximal jejunum