Incidental cysticercosis in a pet rabbit

Emily Brouwer, Marina Brash

Animal Health Laboratory, University of Guelph, ON

AHL Newsletter 2019;23(4):15.

A four-year-old, male castrated, Dutch cross domestic rabbit presented to the submitting veterinarian for cystotomy to remove uroliths. On presentation, the rabbit was in good body condition with no significant findings on preanesthetic physical examination or blood tests. The rabbit was routinely anesthetized, and the abdomen surgically approached via a 3 cm long caudal ventral midline incision. Upon entering the abdomen, three abnormal cystic structures were identified. All cystic structures were free-floating in the abdomen and had no visible vascular attachments. The three cysts were removed, and a biopsy sample of the bladder wall was collected for histology (Fig. 1A). Grossly, these cysts were thin-walled, contained clear fluid, and each had a thickened white asymmetrical linear focus in the wall. Each cyst was fixed in formalin, and routinely processed for histologic examination. Histologically, the cysts contained flocculent eosinophilic fluid surrounded by a thick, fibrous capsule. Corresponding to the white area noted grossly are cestode larvae with convoluted hyaline cuticle overlying palisading epithelial cells and loose mesenchyme containing faint basophilic crystalline concretions (calcareous corpuscles). Scolices had prominent refractile hooks (Fig. 1B).

These cysts were determined to be histologically characteristic of encysted tapeworm larvae. In rabbits, this is most likely Cysticercus pisiformis, the larval stage of Taenia pisiformis. Rabbits are the intermediate host for a variety of carnivore tapeworm species, but the most likely species (T. pisiformis) has the dog as the definitive host. Dogs become infected with the adult tapeworms and release ova into the environment through the feces, which are then ingested by the rabbit. It is unknown if this rabbit had access to an outdoor space that was shared with canids, or if the household had dogs as well. Typically, these infections are incidental, where cysts are identified during abdominal surgery or postmortem. Less frequently, there can be clinical signs related to mass-effect if there is a heavy burden. Lethal cysticercosis is rare in rabbits, but has been described in cases of extensive hepatic parenchymal involvement.

Figure 1. A Free-floating cysts identified in the abdomen (right). The tissue on the left is a biopsy of the urinary bladder. B. Encysted tapeworm larva with prominent hooks (H&E 2X magnification).

References

1. Barthold SW et al. Parasitic diseases. In: Barthold SW et al, eds: Pathology of Laboratory Rabbits and Rodents, 4^th ed. Chichester,UK: Wiley Blackwell, 2016.

2. Graham-Brown J et al. Lethal cysticercosis in a pet rabbit. Vet Rec Case Rep, 2018; 6e000634.doi:10.1136/vetreccr-2018- 000634.