Spirocerca lupi

Spirocerca lupi, the esophageal worm, is a mammalian parasite found in the tropic warm temperate areas and throughout the United States. Their distribution is sporadic, as they have also been found in northern regions of the Soviet Union and Manchuria. (Frisby, 2001; Roberts and Janovy, 2000)

Spirocera lupi most commonly plauge canids and wild felids in warm climates. However they have also been found in northern regions of the Soviet Union and Manchuria. (Roberts and Janovy, 2000)

Spirocerca lupi adults are cylindrical and range from a bright pinkish to red color. The mouth is sorrounded by six lips. Spirocerca lupi also have a well developed buccal capsule with thick walls. Females are approximately 5 to 8 cm long while males are slightly smaller, 3 to 5. 5 cm long. Cyndrical encapsulated juveniles that are passed out through the definitive host feces are 30-38 x 11-15 micrometers.

An outer cuticle has three main non-cellular outer layers made of collagen and other compounds that are secreted by the epidermis. The cuticle layer protects the nematodes so they can invade the digestive tracts of animals.

Nematodes have longitudinal muscles along the body wall. The muscles are obliquely arranged in bands. Dorsal, ventral and longitudinal nerve cords are connected to the main body of the muscle. (Brusca and Brusca, 2003; Roberts and Janovy, 2000)

Embroynated S. lupi eggs exit the definitive host via feces. An intermediate host, a coprophagous (dung-eating) beetle, ingests the eggs while feeding. Inside the egg, the larva develops into an infective third stage and encyst in the intermediate host's tissues. The beetle is then eaten by a definitive host or by a paratenic host (lizard, chicken or mouse), which in turn is eaten by a definitive host. The third stage larva penetrates the stomach wall of the definitive host and migrates through the gastric wall and continues until it reaches the thoracic aorta within 20 days. It remains in the thoracic aorta for 2 to 3 months. After further development, they move to the esophagus where the larva becomes surrounded by a cystic nodule. At this point they can further develop and reach sexual maturity. (Frisby, 2001; Roberts and Janovy, 2000)

Adults are often found in clusters where mating occurs. Spirocera lupi are dioecious and after male and female find each other, via chemotactic an thigmotactic mechanisms, the males caudal papillae detects the female vulva. The male coils around a female with his curved area over the female genital pore. Males have copulatory spicules which they insert into the vulva. They do not conduct sperm, but hold the vulva open while the ejaculatory muscles inject sperm into her reproductive tract. Nematode sperm are amoeboid-like and lack flagella. (Brusca and Brusca, 2003; Pearse and Pearse, 1987; Roberts and Janovy, 2000)

Spirocerca lupi migrate through their host by contracting and relaxing dorsal and ventral muscles. This forces the body into a series of curves producing an s-shaped motion. Adults are often found in clusters where mating occurs. Spirocera lupi are dioecious and after male and female find each other, via chemotactic an thigmotactic mechanisms, the males caudal papillae detects the female vulva. Males have copulatory spicules which they insert into the vulva. They do not conduct sperm, but hold the vulva open while the ejaculatory muscles inject sperm into her reproductive tract. (Pearse and Pearse, 1987; Roberts and Janovy, 2000)

Nematodes within the Secernentea have phasmids, which are unicellular glands. Phasmids likely function as chemoreceptors. Females may produce pheromones to attract males.

Nematodes in general have papillae, setae and amphids as the main sense organs. Setae detect motion (mechanoreceptors), while amphids detect chemicals (chemoreceptors). (Brusca and Brusca, 2003; Roberts and Janovy, 2000)

Parasitic nematodes feed on blood, tissue cells and fluid, intestinal contents or some combination of these. They also feed extravagantly with much waste. Spirocera lupi ingest food through their six lip mouth. A wave of muscle contractions pulls food into the digestive system. Pharyngeal glands and intestinal epithelium produce digestive enzymes to feed on the body fluids. Extracellular digestion begins within the lumen and is finished intracellularly. (Brusca and Brusca, 2003; Pearse and Pearse, 1987; Roberts and Janovy, 2000)

These parasites are usually not preyed on directly, but are ingested from host to host. Larval mortality is high as most of the parasites do not reach appropriate hosts.

Spirocerca lupi eggs exit the definitive host (canine) via feces. An intermediate host, a coprophagous (dung-eating) beetle, ingests the eggs while feeding. Inside the egg, the larva develops into an infective third stage and encyst in the intermediate host's tissues. The beetle is then eaten by a definitive host or by a paratenic host (lizard, chicken or mouse), which in turn is eaten by a definitive host. (Frisby, 2001; Roberts and Janovy, 2000)

Dogs infected with the esophageal worm can be severely damaged and even die. Nodules in an infected host can inhibit swallowing, breathing, and blood circulation. The dog may lose its appetite and weight or even have an aneurysm. Spirocerca lupi may also lead to the development of cancer and occasionally hypertrophic pulmonary osteopathy, inflamed and swollen joints. (Frisby, 2001; Roberts and Janovy, 2000)

Signs of infection in dogs are vomiting, weight loss, and hemoptysis (coughing and spitting up blood). Eggs of S. lupi can also be found in feces or vomit. Endoscopic exams and x-rays can reveal the presence of nodules caused by the esophageal worm. Veterinarians treat infected animals with the drug disophenol. However, irreversible damage, such as a severe aneurysm or cancer cannot be treated effectively. (Frisby, 2001; Roberts and Janovy, 2000)