Current Advice on Parasite Control:
Parasites of Other Systems - Urinary Tract Nematodes
Pearsonema plica (= Capillaria plica)
Pearsonema plica (= Capillaria plica)
Pearsonema feliscati (= Capillaria feliscati)
These parasites are more commonly found in various wild carnivores including raccoons, wild canids, mustelids, etc. For example, in endemic areas, mink and other mustelids commonly serve as hosts for Dioctophyme renale.
Overview of Life Cycle
- Undeveloped eggs of Pearsonema spp. and Dioctophyme renale are passed in the urine of an infected animal, develop first-stage larvae, and require an annelid before becoming infective to the next dog or cat host. The life cycle of Pearsonema spp, is not completely understood, but available data suggest that the eggs must be ingested by an earthworm to allow the first-stage larvae to hatch and become infective to the definitive host. The dog or cat may acquire infection after ingesting infected earthworms, paratenic hosts containing larvae, or material contaminated with macerated earthworm material. Adult Pearsonema spp. develop in the urinary bladder mucosa. Eggs appear in the urine as early as two months following infection.
- Larvated Dioctophyme renale eggs must be ingested by an aquatic oligochaete annelid for infective larvae to develop. Dogs may be infected with D. renale by ingesting these infected aquatic oligochaetes. However, because these oligochaetes generally live in detritus at the bottom of ponds or lake, infection more likely occurs following ingestion of paratenic hosts, such as fish or frogs that fed upon infected annelids. Larvae migrate through the liver of the dog and enter the kidney where the large adult worms develop. Eggs pass into the renal pelvis and exit the dog in the urine. Adult D. renale also are reported from the abdominal cavity of infected dogs; in these cases, there is no route for the eggs to exit the dog.
- egg showing the characteristic flattened bipolar plugs
- adult Pearsonema plica in the urinary bladder mucosa
- barrel-shaped egg of D. renale with the characteristic indistinct bipolar plugs and heavily pitted surface. These eggs are typically passed after the zygote has undergone its first division and hence contain two cells.
- adult D. renale, aptly called the giant kidney worm, removed from the kidney of a dog
- Pearsonema spp.
- Most infections with urinary tract nematodes are subclinical. In heavy infections, Pearsonema spp. can irritate the bladder mucosa, resulting in submucosal edema and subsequent cystitis.
- Adult Pearsonema spp. are occasionally found within the ureters or renal pelvis. The large adults of D. renale will cause pressure necrosis and ultimately destruction of the renal parenchyma. Infected dogs may develop dysuria, hematuria, and lumbar pain. However, because infection is usually unilateral and the unaffected kidney compensates through hypertrophy, clinical disease is not apparent in most cases.
- Dioctophyme renale in the abdominal cavity has been associated with traumatic damage to the liver, hemoperitoneum, and peritonitis, the latter related to egg deposition in the peritoneal cavity.
- While occasionally diagnosed, infection with urinary nematodes is relatively uncommon in dogs and cats and may have more of a regional distribution. For example, Pearsonema spp. appears to be more common in the southeastern U.S., whereas D. renale is more often seen in the northern Midwest and southern Canada. These nematodes are occasionally diagnosed in several dogs in the same cohort when all of the animals in the group ingest a common source of infective larvae.
Host Associations and Transmission between Hosts
- Dogs and cats become infected with Pearsonema spp. via ingestion of infective larvae in earthworms, paratenic hosts, or other material. Dioctophyme renale infection is acquired directly by ingesting the oligochaete annelid intermediate hosts harboring third-stage larvae. However, because the annelids serving as intermediate hosts are found in aquatic detritus, infection may be more frequently acquired via ingestion of third-stage larvae in the tissues of fish or frog paratenic hosts.
Prepatent Period and Environmental Factors
Eggs of Pearsonema spp. appear in the urine of a dog or cat approximately 2 months after ingestion of infective larvae, whereas D. renale infection in the dogs may take 4 to 5 months to become patent.
Site of Infection and Pathogenesis
- Pearsonema spp. are found embedded in the urinary bladder mucosa of dogs and cats, or, more rarely, in the ureters, renal pelvis, or free on the mucosal surface of the bladder. Irritation related to the presence and feeding activity of the nematodes may result in submucosal edema and inflammation.
- Dioctophyme renale develops within the renal pelvis, eventually destroying the renal parenchyma itself via progressive pressure necrosis. Most infections are unilateral and involve only the right kidney. Thus, although pathology from D. renale infection may be severe, in the absence of other disease, the unaffected left kidney compensates and clinical disease associated with renal insufficiency does not develop. In a long-standing infection, the capsule of the affected kidney may contain little more than the adult giant kidney worms and remnants of calcified necrotic renal tissue. Microscopically, mesothelial proliferative lesions containing eggs of D. renale may be seen. The production of sterile eggs by female worms in the abdominal cavity may also cause liver lesions, hemoperitoneum, and peritonitis.
Eggs of the urinary nematodes can be detected via routine examination of urine sediment. Infection with D. renale may also be first detected via appreciation of a grossly distended right kidney on abdominal radiographs or abdominal ultrasound, or serendipitously by finding the large, bright red, adult worms free in the abdominal cavity during a routine laparotomy such as for ovariohysterectomy.
- There are no products labeled for treatment of Pearsonema spp. in dogs and cats; fenbendazole (50 mg/kg) and ivermectin (0.2 mg/kg) have been reported to be effective although several doses may be required to eliminate the infection.
- Because most infections are asymptomatic, treatment of D. renale is usually not pursued; however, surgical removal of the adult nematodes along with the affected kidney or from the peritoneal cavity will eliminate the infection.
Control and Prevention
- Keeping cats indoors and dogs confined to a leash or in a fenced yard will limit the opportunity for pets to acquire infection with Pearsonema spp. from earthworms or paratenic hosts.
- To avoid D. renale infection, do not feed dogs raw or undercooked frogs or fish; also, the refuse from cleaning fish should be secured to prevent scavenging behavior.
Public Health Considerations
- Pearsonema spp. pose no known public health risk. Dioctophyme renale infections have been reported from people who consume raw or undercooked fish or frogs harboring infective larvae.
- Mace TF, Anderson RC. Development of the giant kidney worm, Dioctophyma renale (Goeze, 1782) (Nematoda: Dictophymatoidea). Canadian Journal of Zoology 53: 1552-1568; 1975.
- Measures LN, Anderson RC. Centrarchid fish as paratenic hosts of the giant kidney worm, Dioctophyma renale (Goeze, 1782), in Ontario, Canada. Journal of Wildlife Diseases 21: 11-19, 1985.
- Rossi M, Messina N, Ariti G, Riggio F, Perrucci S. Symptomatic Capillaria plica infection in a young European cat. Journal of Feline Medicine and Surgery 13: 793-795; 2011
- Stainki DR, Pedrozo JCSR, Gaspar LFJ, Zanette RA, Silva AS da, Monteiro SG. Urethral obstruction by Dioctophyma renale in puppy. Comparative Clinical Pathology 20: 535-537; 2011