Rat threadworms

Etiology:  Trichosomoides crassicauda is the bladder threadworm which infects rats.

Incidence:  Incidence of infection is rare.

Transmission:  Transmission occurs by ingestion of ova. Transmission often occurs from parent to weanling offspring.

Distribution:  Urinary bladder, ureter and renal pelvis.

Clinical Signs:  None usually observed. Dead worms may act as a nidus for urinary calculus formation. Migrating larval forms in the lungs may aggravate concurrent respiratory disease.


Antemortem:  Examine the urine for eggs or worms.

Diagnostic Morphology:

Female: 9 – 10 mm long.

Male: 1.3 – 3.5 mm long, lives within the female reproductive tract.

Ova: 55 – 70 x 30-45 µm, brown, thick-walled with bipolar plugs


1. Direct or subgross microscopic examination of urinary bladder.

2. Histopathologic examination of the urinary bladder reveals worms in the lumen or embedded within the transitional epithelium (arrows).

Rat threadworms
Rat threadworms