Gastrointestinal Spirurid Parasites of the Dog and Cat

1. Gastrointestinal Spirurid Parasites of the Dog and Cat

2. Physaloptera spp. Physaloptera is a spirurid nematode that occurs in the stomach and (less commonly) the duodenum of dogs, cats and various wild carnivores. It is reported mainly from the midwestern states where up to 20% incidence can occur . Physaloptera is of rare occurrence in domestic dogs and cats in other areas. Intermediate hosts are crickets, flour beetles, ground beetles and cockroaches. Several species are thought to occur in dogs and cats in the U.S.

3. Histosection of Physaloptera in gastric mucosa Physaloptera spp. are attached to the gastric mucosa where they cause erosions at the point of attachment, gastritis and excess mucous formation. They feed largely on blood. Catarrhal gastritis, vomiting, and loss of condition have been reported. Confusable with ascarids.

4. Anterior and posterior end of Phvsaloptera A very characteristic collar-like cervical alae occurs at the anterior end of the sexes of Physaloptera. Males of Physaloptera have spicules and very large caudal alae as compared to other spirurids. Females have straight tails. The above two slides illustrate characteristics which can be used to differentiate this parasite from ascarids which are of about the same size.

5. Eggs of Physaloptera spp. Stool examinations may reveal oval, thick-shelled, embryonated eggs (49 x 58 by 30-34). For treatment of Physaloptera, literature and informal practice reports indicate efficacy by Dichlorvos (®TASK), Fenbendazole (20mg/kg for 5 days) and pyrantel pamoate (5mg/kg twice, 3 weeks apart).

6. Spirocerca Lupi Spirocerca lupi is a Spirurid parasite that is found in the esophagus, stomach, and aorta of the dog and wild canidae such as the coyote, fox, and wolf . Spirocerca is found in most warm countries of the world and in the United States it occurs primarily in the Southeast. The worms are robust, about 4-5 cm in length, and are red in color .

7. Arthropod Intermediate Hosts Various species of coprophagous beetles (dung beetles) serve as intermediate hosts for Spirocerca lupi.Ova passed in the feces of infected dogs hatch after ingestion by a suitable dung beetle, develop to infective third stage larva, and encyst in the insect's tissues. Infected dung beetles are then ingested by the definitive host, the dog, or anyone of a large number of transport hosts.

8. Transport or Paratenic Hosts An exceptionally wide variety of animals can serve as transport hosts, including various birds, small mammals amphibians, and reptiles.

9. Migration Pattern in the Definitive Host After ingestion, encysted larvae penetrate the wall of the stomach, and migrate in the adventitia of the arteries of the stomach to the thoracic aorta over a three week period.

10. Regional Anatomy This slide illustrates the close proximity of the thoracic aorta to the esophagus and thoracic vertebrae. Most worms migrate (as shown by the arrow) to the wall of the esophagus by traversing the connective tissue or the walls of small arteries. The parasite penetrates completely to the esophageal lumen and then withdraws back into the esophageal wall. This establishes a fistulous communication for later passage of ova to the lumen. Worms generally do not migrate from the aorta to the esophagus until the third month. The final molt to the adult stage also occurs at about this time. Worms are usually in the esophageal wall by the end of the third month and here they cause the formation of a granuloma of variable size. Patency occurs in 5-6 months.

11. Esophageal Granuloma Considerable reaction occurs due to the presence of Spirocerca in host tissues. Esophageal granulomas formed vary from small nodular swellings to large pedunculated masses (as seen here).

12. Ossifying Spondylitis Ossifying spondylitis sometimes occurs in adjacent thoracic vertebrae, apparently due to irritation by migrating larvae.

13. Aortic nodules and aneurisms During the time that parasites are normally in the aorta, or if parasites are arrested in the aorta during migration, they may cause the formation of small nodules or larger, more diffuse granulomas and aneurisms which can rupture leading to fatal extravasation into the abdominal cavity.

14. Ectopic sites As with most migrating parasites, abnormal sites are sometimes reached. Worms may be arrested somewhere along the normal migration route or they may migrate in the wrong vessel or tissues and reach ectopic sites such as the stomach shown here.

15. Associated Sarcoma and Hypertrophic Pulmonary Osteoarthropathy Finally, there is a strong association of Spirocerca with a malignant osteosarcoma or fibrosarcoma. The majority of Spirocerca infections are not clinically apparent and are usually noted at necropsy. Only a small percentage of cases develop sarcomas. The extent of malignant lesions which can develop are seen in this radiograph. (Dense or radiopaque areas). Ossifying spondylitis involving the thoracic vertebrae can also be seen in this radiograph.

16. Factors leading to malignancy: Reasons for the development of Spirocerca sarcomas are poorly understood. It is postulated that metabolic products or some agent carried by this worm interact with host tissues to stimulate neoplasia. Genetic predisposition appears to play a role in the case of hound breeds. Malignancy is most common in older dogs > 5 years old.

17. Hypertrophic Pulmonary Osteoarthropathy If malignancy develops, a common sequela is hypertrophic pulmonary osteoarthropathv (a thickening of the distal long bones associated with a space occupying lesion in the thorax). The dog seen here is severely affected with hypertrophic pulmonary osteoarthropathy (HPO) associated with a thoracic sarcoma. HPO can also occur with large thoracic granulomas due to Spirocerca. Note the formation of less dense new bone on preexisting dense cortical bone.

18. Clinical Signs Clinical signs associated with Spirocerca infections depend on where major lesions develop. A large granuloma may cause persistent vomiting. Aortic aneurisms may rupture and lead to sudden death by extravasation. If malignancy occurs, a wide variety of symptoms may occur depending on the location of the primary neoplasm or metastases. A thorough knowledge of the life cycle of Spirocerca is necessary for diagnosis of disease by this parasite.

19. Epidemiology The slide illustrates the general distribution of reported Spirocerca sarcoma in the Southeast. Incidence of simple Spirocerca infection would follow a similar distribution. Bailey at Auburn recorded an 8% infection rate in Alabama in a survey between 1951 and 1963, but only 2% from 1963-1970. Georgia surveys show less than 1% of the dogs infected. Bailey considered the feeding of uncooked intestinal tracts of chickens to be a primary source of infection for dogs . Incidence of Spirocerca has decreased in recent years due to better care of dogs, the shift to confinement poultry operations, and reduction of dung beetle numbers by large scale use of agricultural insecticides.

20. Diagnosis and Treatment • Diagnosis can be made by: • Clinical signs and history • Radiography with contrast media • Endoscopy • Stool examination • NaNO3 Flotation (1.36 specific gravity) - Sugar and NaCl solutions are less effective. Treatment: Disophenol 1 ml/10 lb. for 10 days is effective against adult worms.

21. Egg of Spirocerca lupi Note the small size, thick wall and larvae. A whipworm egg is also present. Recovery of eggs is dependent on a patent opening to the lumen of the digestive tract and therefore ova are not consistently found. Spirocerca worms do not live more than a few years and lesions do not always contain worms at necropsy.