Page 121 - Medical Parasitology_ A Textbook ( PDFDrive )

114 10 Nematodes: Roundworms

Adult worm resides in the tumours or granulomatous lesions in the stomach
wall of cat and dog. Eggs are laid in the tumours. Eggs pass into gastric lumen
and are discharged in faeces into water, where they hatch into first stage larva
(L1). L1 larvae are ingested by cyclops (first intermediate host) where the sec-
ond-stage larvae develop. Cyclops are eaten by the second intermediate host:
fish frogs and snakes, where the third-stage larvae develop (L3). When the L3
larvae are eaten by cats, dogs, or other suitable hosts, the larvae develop into
adults inside their body. When other paratenic hosts (reptiles, birds, or mam-
mals) get infected, the larva does not undergo any further development. Humans
acquire infection by eating undercooked fish containing third-stage larvae.
They are unable to complete their development as human is a paratenic host
and they migrate in the skin, subcutaneous tissue or other organs.

Pathogenesis and Clinical Features
After ingestion of the larva, its migration may produce epigastric pain, fever and
vomiting. The migration of larvae in the tissues may lead to visceral gnathostomia-
sis and cutaneous lesion. Superficial nodules can be incised and the larvae removed.
The migrating larvae may reach the brain causing eosinophilic meningoencephalitis
or reach the eyes causing severe damage.

Diagnosis
The lesion can be biopsied. Presence of larva confirms the diagnosis.

Treatment
Removal of larva via surgery. Albendazole (400 mg daily for 21 days) or mebenda-
zole is recommended.

Prevention and Control
1. Avoid eating uncooked fish, frogs, or snakes

Anisakis

Distribution
Anisakis species are nematode parasites of marine mammals like dolphins, seals and
whales. Anisakiasis is common in Japan and other places where fresh or under-
cooked infected marine fish is eaten containing larvae of the nematode Anisakis
simplex.

Habitat
In human, the parasite is found in the gastrointestinal tract.

Morphology
Anisakis are free-living, non-segmented, cylindrical worms. The third-stage larvae
may reach a length of 50 mm and a diameter of 1–2 mm. It has a boring tooth ventral
to the mouth.