Microscopy

The eggs of Ancylostoma and Necator cannot be differentiated microscopically.  The eggs are thin-shelled, colorless and measure 60-75 µm by 35-40 µm.

A	B

A, B:  Hookworm eggs in unstained wet mounts, taken at 400× magnification.

C	D

C:  Hookworm egg in an unstained wet mount.
D:  hookworm egg viewed under UV microscopy.

Rhabditiform (L1) larvae that hatch from eggs are 250-300 µm long and approximately 15-20 µm wide.  They have a long buccal canal and an inconspicuous genital primordium.  Rhabditiform larvae are usually not found in stool, but may be found there is a delay in processing the stool specimen.  If larvae are seen in stool, they must be differentiated from the L1 larvae of Stronyloides stercoralis.

E	F

E, F:  Hookworm rhabditiform larvae (wet preparation).

Infective, third-stage (L3), filariform larvae are 500-600 µm long.  They have a pointed tail and a striated sheath.  These L3 are found in the environment and infect the human host by penetration of the skin.

G	H

G, H: Hookworm filariform larva (wet preparation).

Adult hookworms reside in the small intestine of their hosts.  Males measure approximately 8-12 mm long and are bursate, with two spicules that do not fuse at their distal ends.  Females measure approximately 10-15 mm long.  Adults of both sexes have a buccal capsule containing sharp teeth.

I	J

I:  Adult worm of Ancylostoma duodenale.  Anterior end is depicted showing cutting teeth.
J:  Adult worm of Necator americanus.  Anterior end showing mouth parts with cutting plates.

K	L

K:  Anterior end of an adult of Ancylostoma caninum, a dog parasite that has been found to produce a rare human infection known as eosinophilic enteritis.
L:  Anterior end of an adult female Ancylostoma sp.