Bladder Threadworm in Rats

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Urinary Nematodiasis in Rats

A common urinary disease in rat colonies is nematodiasis. This occurs when the nematode parasite Trichosomoides crassicauda infects the rat's urinary bladder, causing painful urination, stunted development, and stones in the bladder (bladder calculi). Kidney diseases like pyelitis, renal pelvic inflammation and stones in the kidney (uroliths) may also occur if the parasite (threadworm) moves upward toward the bladder.

The source of infection is contact with Trichosomoides crassicauda eggs that have been passed in the urine of infected rats. Typically, nematodiasis occurs in rats older than two to three months and is resolved with the insecticide ivermectin. Reinfection can be prevented by maintaining hygienic living conditions with proper sanitation.


Symptoms and Types

  • Painful urination (dysuria)
  • Stones in the bladder and/or kidneys
  • Failure to develop properly
  • Sudden or chronic renal pyelitis
  • Renal pelvic inflammation
  • Bloody urine due to stone formation

The male threadworm attaches itself to the lumen of the rat’s bladder and the female threadworm attaches itself to the lumen and mucus membrane of the bladder. The male threadworm can sometimes even live insides the uterus of the female threadworm. The male threadworms grow to be 1.5 to 2.5 millimeters in length, while the female threadworm can be as long as 10 millimeters (1 centimeter).


  • Infection with the threadworm, Trichosomoides crassicauda
  • Contact with eggs of the parasite through the contaminated urine of infected rats
  • Unsanitary living conditions


Bladder threadworm is usually diagnosed by conducting urinary tests and examining the urine for the presence of eggs of the parasite.

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