Worms Gone Wild

Coby Richter, DVM, DACVS, outlines a case involving tapeworm segments free-floating in the abdomen and coating almost all of the abdominal organs.

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A 7 ½ year old neutered male pit bull terrier was examined by his regular veterinarian for a 5 day history of a “swollen” abdomen. The abdominal distention had progressed during this time and was accompanied by a poor appetite of two days duration and at least one episode of vomiting. There was no unusual travel history or change in diet and the dog was not known to be an indiscriminate eater. Physical examination revealed a severely distended abdomen, though not tympanic, with an obvious fluid wave. The dog did not appear painful on abdominal palpation. Due to the degree of distension, discrete organ palpation was not possible. Muscle wasting was also noted and the owners observed that he spent more time resting and being quiet than usual. The only abnormality found on a complete blood count was a monocytosis (21% of total WBC of 6000 cells/microliter). A chemistry panel demonstrated mildly elevated alanine aminotransferase (ALT) = 153 IU/L and aspartate aminotransferase (AST) = 69 IU/L. Abdominocentesis recovered 985 ml of yellow, flocculent fluid and was discontinued to allow the patient to equilibrate to fluid loss. Free catch urinalysis was unremarkable except for mild bilirubinuria (2+ on dipstick). Cytological analysis of the peritoneal fluid revealed 3520 nucleated cells/Liter and a protein of 2.3 g/dl. Microscopic examination of the white flocculent material in the fluid revealed intact and fragmented Mesocestoides sp. organisms. Many fragments contained yellow round refractile spherules (consistent with calcareous corpuscules). No evidence of neoplasia or bacteria was found. In light of the diagnosis of cestodiasis, the dog was started on fenbendazole at 100 mg/kg orally twice daily. His appetite continued to decline and he became more lethargic over the following 4 days. Abdominal distention progressed and his owners felt that the dog was beginning to exhibit difficulty breathing. He was referred to DoveLewis for abdominal exploration and mechanical lavage. Bloated patient pre-op isolation

Thoracic and abdominal radiography and abdominal ultrasound were discussed with the owners and referring veterinarian. The goal of surgery was to assess organ involvement and to decontaminate via mechanical lavage as much as possible prior to long term treatment with an oral anthelmintic. Due to the vast amount of effusion, neither ultrasonography nor abdominal radiography was expected to give enough conclusive evidence for the clients to elect euthanasia rather than exploratory surgery. Radiographs of the thorax would have been useful to assess the lungs prior to anesthesia however the owners wished to proceed directly to surgery.

Tapeworm suction bucketExploratory celiotomy was performed. Immediately upon entering the abdomen, 3 liters of flocculent yellow fluid was suctioned to control contamination of the surgical suite. All serosal surfaces were covered with severe fibrinous peritonitis and villous proliferation of the mesothelium (“shag rug” appearance). All lobes of the liver, the spleen, stomach, small and large intestine, urinary bladder, pancreas, diaphragm, and body walls from diaphragm to inguinal region were coated with a thick carpet of fibrin and pyogranulomatous inflammation, punctuated with small white spherical structures varying in size from 1mm to 10 mm. The spleen was coiled in a donut shape and tightly adhered to the stomach. The small intestine was adhered to itself in multiple sites creating sharp turns and obvious challenges to normal progression of ingesta. No motility was seen in the small or large intestine during surgery. Efforts to debride the thick (3–10mm) layer of inflammatory debris, cysts and mesothelial proliferation were unrewarding. During exploration, the abdomen was lavaged with 11 liters of warmed saline. Efforts were made to keep the flocculent material in suspension so it could be removed by suction; however the 11th liter was still 5–10 % white debris (tape worm segments). Due to the grave prognosis for long term survival, the owners elected humane euthanasia during surgery.

Patient full of worms in surgeryPeritoneal cestodiasis is an uncommon disease of dogs, cats and other carnivores (foxes, mink etc.). While this case ultimately ended in a sad choice for the clients and an early death for their dog, it is an important reminder to the veterinary community of the zoonotic potential of this disease. Since the diagnosis of peritoneal Mesocestoides had been made prior to referral to DoveLewis, we had the advantage of being able to plan, prepare and discuss the protocol for handling the patient and the expected large volume of biologic hazardous material (peritoneal fluid etc.). A brief review of the life cycle of this tapeworm can aid in determining how to best protect yourself and personnel from infection. Mesocestoides requires two intermediate and one definitive host. The egg (containing first larval stage) is consumed by a coprophagous arthropod where it develops into the second larval stage. The arthropod is then ingested by the second intermediate host such as a frog, mouse or bird. The second larval stage develops to the third larval stage (tetrathyridium) in the peritoneal cavity of the host. The adult worm develops within the intestines approximately 2–3 weeks after ingestion of second intermediate host by the definitive host (dog, cat, fox etc). Peritoneal infection can occur in both the second intermediate (where the tetrathyridium perforates the intestine and enters the peritoneum) and the definitive host (where the adult worm enters the peritoneal cavity) and the dog can serve as either. Humans enter the cycle as a possible definitive host after ingestion of the third larval stage (fecal–oral or abdominal contents—oral routes).

When this patient was referred to DoveLewis, we designated a minimum number of staff that would handle the dog and he was immediately assigned a large biohazard container (30 gallon garbage can lined with a biohazard bag and well identified). Although the infectious material would mostly be collected in surgery, it was felt that implementing the process right from admission would be most effective. Prior to surgery, only feces would present a potential hazard. Handlers wore disposable isolation gowns and gloves when interacting with the dog. In surgery all personnel used eye shields or goggles in addition to standard protective gear. While direct ocular infection is not a known means of transmission for Mesocestoides, goggles served as an additional level of awareness and protection during the period of greatest exposure. During surgery, every attempt was made to collect the abdominal fluid by suction and allow as little as possible to wet drapes or huck towels. As suction containers were filled, they were transferred to a 5 gallon closed bucket pre–filled with 1 inch of 10% formalin. Surgical personnel were not to leave the suite once the abdomen was open to reduce the potential for tracking contaminants into other parts of the hospital. At the end of surgery, all disposable surgical drapes, huck towels, lap sponges, gauze sponges, plastic instruments or tubing etc were collected into the original biohazard container. All metal instruments were cleaned in standard fashion and the surgical suite sterilized as we would for any contaminated surgical procedure. The biohazard bags were collected for incineration the following day. Naturally, all personnel involved in handling the dog were notified before starting surgery about the zoonotic potential and encouraged to wash their hands regularly and to change scrubs after the procedure.

Diagnosis generally relies on peritoneal fluid analysis, although results can be falsely negative when organisms become compartmentalized by adhesions or pyogranulomatous inflammation. Also, since the tapeworm segments tend to settle to the bottom of a sample tube, they may be missed if the fluid is not re-suspended prior to analysis. Fecal tests are often negative in infected dogs suggesting dogs are more commonly the second intermediate host than the definitive host (where adult worms in the intestine would be expected to shed eggs). The clinical signs this dog exhibited are typical of peritoneal larval cestodiasis; depression, anorexia, vomiting, diarrhea, weight loss, pyrexia, poor hair coat, ascites, abdominal distension and occasionally dyspnea. Hematologic and serum chemistry values are often non–diagnostic with a mild non–regenerative anemia, monocytosis and hypoproteinemia seen in cases reported in the literature. Larval migration into the viscera is documented in other cases and may result in elevations in organ specific enzymes or may change the character of the peritoneal effusion (e.g. hemorrhage with splenic migration). Successful treatment of peritoneal larval cestodiasis appears to rely on early diagnosis, prior to severe, fibrinous peritonitis, villous proliferation of the mesothelium, serosal adhesions and cyst formation, followed by long term treatment with fenbendazole (3–4 months). Surgery to effect decontamination and mechanical lavage of the abdomen prior to treatment with the anthelmintic is not an easy decision for veterinarian or client. However given the massive amount of tapeworm larvae and cysts that could be harbored in the abdomen, surgical lavage is indicated and is supported by those few cases documented in the literature. Unfortunately, the severity of the inflammatory changes, adhesions and cystic structures was too great in this dog to offer any reasonable chance of quality of life.

DoveLewis would like to thank the veterinarians at Fremont Veterinary Clinic for the referral of this case, and the dog's owners for consenting to the use of his case as an educational tool for our veterinary community.

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