Spirocerca lupi
Holly Frisby, DVM
Veterinary Services Department, Drs. Foster & Smith, Inc.
Spirocerca lives in the esophagus and stomach and can cause cancer of the esophagus and severe damage to large blood vessels. It is widely distributed in the southern United States, and infects dogs, fox, wolves, and lynx. The adult worm is red in color and approximately 3 inches long. The eggs, which contain larvae, have the shape of a paper clip.
What is the life cycle of Spirocerca lupi?
The adult worm lives within nodules in the esophagus and stomach. The eggs it lays contain larvae, which are eaten by beetles. Inside the beetles the eggs hatch and the larvae develop into more mature forms. A dog can become infected by eating the beetle, or eating an animal that ate a beetle. (That's a tongue twister.) Inside the dog, the larva is released and enters the blood vessels and winds its way to the aorta (the large artery carrying blood to the body). It finally migrates from the aorta to the esophagus, and possibly the stomach, completing the life cycle. (The aorta and esophagus lie next to each other in the animal's chest.)
What damage is caused by esophageal worms?
The nodules in infected animals can interfere with swallowing, and if nodules occur in the stomach, vomiting can be seen. The animal may lose its appetite and weight loss can result. Nodules that put pressure on the airways in the chest can cause difficult breathing. Nodules can also put pressure on the blood vessels in the chest, affecting blood circulation. If an adult worm stays in the aorta, the nodule that forms around it could cause an aneurysm (dilation) of the aorta to develop. If the aneurysm would rupture, death would follow quickly.
Nodules caused by Spirocerca lupi can develop into cancer that can spread to other organs. An unusual sign of infection with the esophageal worm is abnormal bony changes and swelling of the legs of the animal. This is called hypertrophic osteopathy. The exact mechanism by which this occurs is unknown, but it is seen when there are tumors or other masses in the chest. Hypertrophic osteopathy may be observed before any digestive or respiratory signs of Spirocerca lupi infection are seen.
Abnormal changes of the vertebrae (bones in the back) may also occur.
How is infection with Spirocerca lupi diagnosed?
Eggs of Spirocerca lupi can be found in the feces or vomit, but sometimes it takes repeat examinations since the worms are not continually releasing eggs. An endoscopic exam of the esophagus will reveal the characteristic nodules. Signs of hypertrophic osteopathy may signal your veterinarian to look for tumors or other masses in the chest. The nodules caused by the esophageal worm can be seen on radiographs (x-rays).
Is there an effective treatment for infection with Spirocerca lupi?
A drug called disophenol has been shown to be effective in treating this condition. The hypertrophic osteopathy will resolve with treatment. Sometimes, however, irreversible damage, such as an aneurysm or cancer has occurred, and can not be treated effectively.
What measures can be taken to prevent infection with the esophageal worm?
Exposure to feces and vomit must be eliminated. Dogs should not be allowed to eat animals that may be transport hosts (animals that may have eaten infected beetles, such as chickens, frogs and rodents). Chickens, especially, have been shown to be an important source of infection in the southern United States. Dogs should not be allowed to eat raw chicken or entrails.
