Stephanurus dentatus (Kidney Worm of Swine)

Stephanurus dentatus (Kidney Worm of Swine): Morphology, Life Cycle, Pathogenesis & Treatment

Stephanurus dentatus, commonly known as the kidney worm of swine, is a parasitic nematode of pigs that primarily inhabits the perirenal tissues, renal pelvis, and ureters. Although pigs are the principal hosts, occasional infections have also been reported in cattle and donkeys. This parasite is widely distributed in tropical and subtropical regions and is of considerable veterinary importance because of its long migratory phase, extensive tissue damage, and associated economic losses in swine production.

The life cycle of Stephanurus dentatus is unique because infection may occur through ingestion of infective larvae, skin penetration, or indirectly through earthworms acting as transport hosts. Larval migration through the liver and other organs causes fibrosis, abscess formation, and reduced growth performance, while adult worms produce eggs that are excreted in the urine. In this article, you will learn the taxonomy, morphology, life cycle, pathogenesis, clinical signs, diagnosis, treatment, and control of Stephanurus dentatus in a concise, veterinary-focused format.

Parasite Overview

• Common Name: Kidney worm of swine
• Host: Pig; rarely cattle and donkeys
• Predilection Site: Perirenal fat, renal pelvis, and the walls of the ureters. As an erratic parasite, it may also be found in the liver, abdominal cavity, thoracic organs, and spinal canal of pigs.
• Distribution: Tropical and subtropical countries

Taxonomical Classification

• Kingdom: Animalia
• Phylum: Nematoda
• Class: Chromadorea
• Order: Strongylida
• Superfamily: Strongyloidea
• Family: Stephanuridae
• Genus: Stephanurus
• Species: Stephanurus dentatus
• Common Name: Kidney worm of swine

Morphology

• Size: 3–4 cm in length.
• Worms are stout, large-bodied, with a mottled appearance and internal organs visible through the cuticle. The buccal capsule is cup-shaped with six cusped teeth at its base.
• The mouth rim bears a leaf crown and six external cuticular thickenings (“epaulettes”).
• The male bursa is small, and the rays are short. The spicules are equal, and the eggs are ellipsoidal.

Life Cycle

It is of particular importance where pigs are raised outdoors because its preparasitic larvae are free-living and may also utilize earthworms as transport hosts.

The adult kidney worms are usually found in pairs within cysts up to 4 cm in diameter in the perirenal fat and pass eggs in the urine, which develop into infective larvae within 2–7 days.

The life cycle can be through:

1. Ingestion of infective larvae
2. Skin penetration
3. Indirectly through ingestion of infected earthworms

The larvae migrate from the intestine and reach the liver via the blood vessels, where they wander for 3 months or more. The Stephanurus larvae then escape from the liver and migrate via the peritoneum to the kidney, where cysts are formed.

Eggs do not appear in the urine until 9–16 months (long prepatent period) after infection. The worms are long-lived and highly prolific; a female may lay eggs for up to 3 years, and as many as 1 million eggs per day may be passed in the urine of an infected pig.

Pathogenesis

• Skin penetration by infective L3 larvae may cause cutaneous nodules and swelling of the superficial lymph nodes.
• Adults are found in pairs within cysts containing green pus. Liver migration produces a marked inflammatory reaction with eosinophilia. Extensive fibrosis results from the migration of larvae and immature adults through the liver. Repair of these lesions results in liver scarring and cirrhosis.
• Migration of immature adults through other organs, such as the pancreas, may result in abscesses, fibrosis, and adhesions.
• Aberrant migration of larvae to the spinal cord may cause posterior paralysis, although this is uncommon.

Clinical Signs

• General signs include reduced growth rate, loss of appetite, poor weight gain, and emaciation.
• The ureter becomes thickened.
• The presence of subcutaneous and precrural nodules causes stiffness of the legs.
• The larvae produce severe liver damage, resulting in loss of appetite and poor body condition.
• Blood may be present in the urine.
• Considerable muscle wasting is also observed.

Significance

Stephanurus dentatus causes significant economic losses due to reduced feed efficiency in growing pigs and carcass trimming of damaged tissues at slaughter.

Diagnosis

Because the parasite has a long prepatent period, diagnosis is difficult in infected pigs. Diagnosis is usually made at necropsy by examination of the kidneys. Eggs can be detected in the urine.

Treatment

No satisfactory treatment is available for Stephanurus dentatus. However, thiabendazole at 0.1–0.4% is effective against migrating larvae.

Control

• Control of the earthworm transport host is essential.
• Raise pigs on concrete floors.
• Herd infections may be prevented by using a “gilts only” breeding system, in which gilts are sold or slaughtered after producing one litter, before they are old enough to harbor adult worms.
• Application of Polyborate at 2.5 kg per 12 L of water per 10 m² of soil kills the eggs and larvae.