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Kidney Worm:
Dioctophymiasis and Eustrongylidiasis

Fishermen have a harmless habit, for which they are renowned all over the world, of exaggerating the size of their catch, especially the one that got away. A few, fortunately a very few, have a habit less harmless, that of swallowing their live bait, particularly minnows. Within 24 hours they become acutely ill, and may claim that they acquired the infection from eating raw fish: this is, in fact, accurate, but perhaps a little misleading. Fortunately dioctophymiasis is a very rare disease in humans.

Synonyms

Giant kidney worm. Dioctophymosis. Eustrongylidosis.

Definition

Dioctophymiasis and eustrongylidiasis are infections by the nematodes in Dioctophymatoidae, including D. renale and Eustrongylides spp.

Geographic Distribution

These nematodes are found worldwide, but surprisingly less common in Africa and Oceania. The largest number of cases have been reported in Iran. The worm infects mammals worldwide, particularly the mink and dogs, but also cats, wolves, oxen and horses, raccoons and skunks, and even pumas. Fresh-water frogs and fish are a frequent source of infection for humans, up to 50% of minnows being infected in some areas.

Epidemiology and Pathology

D. renale is a large red worm (20 to 100-cm by 5 to 12-mm in the case of the females; the males are smaller, 14 to 20-cm. The life cycle includes an intermediate host and the definitive host is a mammal. Eggs are voided in urine and the first-stage larva develops in 15 to 100 days. These embryonated eggs are then ingested by the aquatic intermediate host and the larvae molt twice before they are infected. In the definitive host, the carnivore or other mammal, the larvae penetrate the mucosa of the stomach and migrate to the liver and the peritoneal cavity, eventually reaching the kidney. It may take 50 days before the kidney is infected: eggs cannot be released except through the kidneys.

There are about 20 authenticated human infections in which the worms have been identified in subcutaneous nodules, usually in the patient's chest or abdominal wall. The adults live in the renal pelvis and are released in the urine. They cause gradual destruction of the kidney, showing clinically as renal colic and hematuria.

Eustrongylides are parasites of fish-eating birds. The life cycle is very similar to that of D. renale.

Laboratory Investigations

The diagnosis is made by recognizing the adult worm in tissue sections. Eggs have been discovered in the urine and in ascitic fluid. The size, color, and location of the worm in the urinary tract are important. The differential white cell count shows eosinophilia but is otherwise normal. There are no other significant laboratory findings.

Clinical Characteristics

Renal colic and low back pain are the usual presenting symptoms, accompanied by hematuria and pyuria. An adult worm may be recognized in the urine. Appendicitis is often the clinical diagnosis. A Eustrongylides infection causes severe abdominal pain, often in the right lower quadrant and seldom lasting beyond 24 hours. Most patients are afebrile. Some patients vomit. Unless the worm is identified in the urine, accurate diagnosis is difficult.

Three cases have been reported in which the worm was subcutaneous. The complaint was of a lump on the chest or abdominal wall and the larvae were found after excision. The tissue reaction surrounding the worm was an eosinophilic granulomatous inflammation.

At surgery the reddish-pink worms may be seen moving in the peritoneal cavity, or in the kidney. One patient in China had a large retroperitoneal mass above the right kidney.

Imaging Diagnosis

The mass above the right kidney (described above) was found on CT and ultrasonography. Contrast urography was normal. Unless the kidney infection has progressed, it is unlikely that there will be any specific changes on contrast urography or other imaging.

The possibility of these worms will have to be included in the differential diagnosis of a mass in the kidney or abdomen, particularly if the patient is a fisherman.

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Copyright: Palmer and Reeder