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 (arrow).