Atlas of livestock parasites
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Stephanurus dentatus



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Stephanurus dentatus
Kidney worm

General Description:
The kidney worm is stout-bodied and 2 to 4 cm long. The internal organs show through its body wall, giving the worm a mottled appearance.

Life Cycle:
The adult kidney worms are usually found in pairs in cysts up to 4 cm. in diameter in the kidney or adjacent fat. Eggs laid by the adult female pass out with the urine and hatch in 2 days. Infective third-stage larvae develop in 4 days and may infect swine by penetrating skin or by being ingested. In addition, earthworms may ingest and accumulate larvae. Pigs may acquire large infections by eating worms containing many larvae. After breaking through the skin or the intestine of pig hosts, the larvae migrate via blood vessels to the liver, where they wander for 3 months or more. The Stephanurus larvae then escape from the liver and migrate through the peritoneum to the kidney where cysts are formed. Eggs do not appear in the urine until 9 to 16 months after infection. The worms are long-lived and very prolific; a female may lay eggs for 3 years, and up to 1 million eggs per day may be passed in the urine of an infected pig.

Adult Stephanurus live in cysts in the kidney or nearby fat; larvae migrate through the liver.

Geographical Distribution:
Primarily in warm regions, especially tropical and subtropical areas, as the larvae are very susceptible to cold.

The kidney worm is of major importance when planning a herd treatment regime for afflicted areas. This parasite causes heavy losses due to low feed efficiency in feeder pigs and to carcass trimming of damaged tissues at slaughter.

Effect on Host:
Severe damage is caused by the extensive wandering of larvae within the liver. General signs include de¬pressed growth rate, loss of appetite, and emaciation. Muscle stiffness may also be present.

Diagnostic Information:
During the long prepatent period, clinical signs may be present but no eggs can be found in the urine. Diagnosis can be made at necropsy or slaughter.

Control of the earthworm transport host is also critical. Raising swine on concrete could virtually eliminate the kidney worm problem. Herd infections may be prevented by the use of a „gilts only" breeding system, in which gilts are slaughtered after they produce one litter, before they are old enough to harbor adult worms. Although this system will eliminate Stephanurus in under 2 years, it is generally unprofitable because of the small size of gilt litters. Drug treatment programs in operations that maintain breeding stock are important because the major reproducing worm population is found in older pigs owing to the lengthy prepatent period. These pigs generally show no recognizable signs of infection, and will maintain a highly infective kidney worm population. Feeder pigs which are infected by the larvae or eat infected earthworms will exhibit characteristic non-specific poor growth.


Stephanurus: adults
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Stephanurus: kindey worm
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Stephanurus: liver lesions
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Stephanurus: liver lesions with larvae
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