Intestinal Nematodescontinued Clinical Microbiology Review 249
NEMATODE ROUTE OF INFECTION DIAGNOSTIC STAGE OTHER
Ascaris lumbricoides Most common helminth worldwide.
Often seen with Trichuris. Eggs require
several weeks in soil to become infec-
tive. Larval migration through lungs.
Adult resembles earthworm. May pass
from anus, mouth, or nose.
Eosinophilia.
Ingestion of infective ovum. Fertilized ovum: ovoid. 50–75 μm
× 40–60 μm. Yellow to brown.
Granular yolk. Clear zones at either
end. May have mammillated cover-
ing or be decorticated.(From Leventhal R, Cheadle RF. Medical
Parasitology: A Self-Instructional Text, 5th ed.
Philadelphia: FA Davis; 2002:20.)continued...