Capillaria plica may infect the urinary bladder, and occasionally the ureters and renal pelvises, of dogs and cats. Distribution is worldwide, and wild animals appear to be the primary hosts. A similar but less common organism, C felis cati, is also found in cats. Dogs and cats become infected by eating earthworms that contain the first-stage larvae. Mature Capillaria are threadlike, yellowish, and 13–60 mm long. The eggs are colorless, operculated, have a slightly pitted shell, and are 63–68 × 24–27 μm in size. Most dogs and cats are asymptomatic. Some animals show signs of pollakiuria, urinary incontinence, and urinating in abnormal places. The eggs are shed in the urine and may be found in the urine sediment. Microscopic hematuria and increased numbers of epithelial cells may also be present. Reported treatments include levamisole, fenbendazole, albendazole, and ivermectin. The treatment of choice is unknown, but a single dose of ivermectin at 0.2 mg/kg, SC, is likely to be effective. It is not FDA-approved for this use and is contraindicated in Collie breeds. The parasite may be self-limiting in the absence of reinfection.
Last full review/revision July 2011 by Melissa S. Wallace, DVM, DACVIM