Adult Spirocerca lupi are bright red worms, 40 mm (male) to 70 mm (female) long, generally located within nodules in the esophageal, gastric, or aortic walls. Infections are seen in southern areas of the USA as well as in most tropical regions worldwide. Dogs are infected by eating an intermediate host (usually dung beetle) or a transport host (eg, chickens, reptiles, or rodents). The larvae migrate via the wall of the celiac artery to the thoracic aorta, where they usually remain for ∼3 mo. Eggs are passed in feces ∼5–6 mo after infection.
Most dogs with S lupi infection show no clinical signs. When the esophageal lesion is very large (usually when it has become neoplastic), the dog has difficulty swallowing and may vomit repeatedly after trying to eat. Such dogs salivate profusely and eventually become emaciated. In addition, dogs may develop thickening of the long bones characteristic of hypertrophic osteopathy. These clinical signs are suggestive of spirocercosis with associated neoplasia in regions where the parasite is prevalent. Occasionally, a dog dies suddenly as the result of massive hemorrhage into the thorax after rupture of the aorta damaged by the developing worms.
The characteristic lesions are aneurysm of the thoracic aorta, reactive granulomas of variable size around the worms in the esophagus, and exostoses that bridge between ventral aspects of thoracic vertebrae. Esophageal sarcoma, often with metastases, is sometimes associated (apparently causally) with S lupi infection, particularly in hound breeds. Dogs with Spirocerca-related sarcoma often develop hypertrophic osteopathy (see Hypertrophic Osteopathy in Small Animals).
Diagnosis can be made by demonstrating the characteristic small (11–15 × 30–38 μm), elongated eggs (by NaNO3 [specific gravity 1.36] or sugar flotation) that contain larvae in the feces. However, eggs are sporadically voided in feces and can be difficult to find. Gastroscopy occasionally reveals a nodule or an adult worm. A presumptive diagnosis can be made by radiographic examination when it reveals dense masses in the esophagus; a positive-contrast barium study may help define the lesion.
Many infections are not diagnosed until necropsy. The granulomas vary greatly in size and location in the esophagus but usually are sufficiently characteristic to be diagnostic, even if the worms are no longer present. Worms and granulomas may be present in the lungs, trachea, mediastinum, stomach wall, or other abnormal locations. Healed aneurysms of the aorta persist for the life of the dog and are diagnostic of previous infection. When sarcomas are associated with the infection, the esophageal lesion usually is larger and often contains cartilage or bone; metastases frequently are present in the lungs, lymph nodes, heart, liver, or kidneys.
Treatment and Control
In endemic areas, dogs should be prevented from eating dung beetles, frogs, mice, lizards, etc, and not fed raw chicken scraps. Treatment is often not practical. However, efficacy has been demonstrated with doramectin (0.2 mg/kg, SC, 3 doses at 2 wk intervals; 0.4 mg/kg, SC, 6 doses at 2-wk intervals; 0.5 mg/kg, SC, 2 doses 2 wk apart; 0.8 mg/kg, SC, 2 doses 1 wk apart; additional treatments may be required), and ivermectin (0.6 mg/kg, SC, 2 doses 2 wk apart) combined with prednisolone (0.5 mg/kg, PO, bid for 2 wk and then tapered), although all these treatments are not approved. The specific breed toxicity associated with ivermectin in Collies and other herding dog breeds also occurs with doramectin. Surgical removal usually is unsuccessful because of the large areas of the esophagus involved.
Last full review/revision March 2012 by Andrew S. Peregrine, BVMS, PhD, DVM, DEVPC