Oesophageal Worm

(Spirocerca lupi)

Spirocerca lupi is a grossly underestimated and potentially fatal spirurid nematode of domestic and wild canids. Dogs become infected when they ingest intermediate (dung beetles) or transport hosts (e.g. chicken offal, reptiles and rodents).

Parasite: Spirocerca lupi
Common name: Oesophageal worm
Host: Canids
Pre-patent period: 5-6 months
Location of adults: Oesophageal and stomach wall
Distribution: Tropical and subtropical regions
Transmission route: Ingestion of intermediate or paratenic (transport) hosts
Zoonotic: No

Distribution

Spirocerca lupi is widely distributed in tropical and subtropical regions of Asia, Oceania, Latin America, Africa and the Middle East.

Clinical signs

Infected dogs may initially be asymptomatic but may progress to having regurgitation, vomiting, melena, wasting and weight loss as a result of the granulomatous masses in the oesophagus and stomach (Fig 1). Aortic migration of larvae may lead to pleuritis resulting in coughing, retching and dyspnoea. Aortic aneurysms (Fig 2) may occasionally rupture causing thoracic haemorrhage and sudden death.  Fibrous nodules in the oesophagus and stomach may undergo malignant transformation and progress to oesophageal sarcoma with secondary metastases. Hypetrophic osteopathy with front leg periosteal calcification is commonly found associated with a thoracic space occupying lesion in dog with S. lupi-associated neoplasia.

Figure 1. Infection with Spirocerca lupi can cause granulomatous masses in the oesophagus and stomach. (Image credit: The University of Melbourne parasitology image library.)
Figure 2. Aortic aneurisms in a dog caused by larvae of migrating Spirocerca lupi. (Image credit Dr Rebecca Traub.)

Diagnosis

Faecal egg shedding is intermittent or absent if nodules lack a fistula. Detection of characteristic ellipsoid embryonated eggs (small, 35 × 15 μm) in faeces (Fig 3) by standard flotation (SOP 1) using a solution with S.G. > 1.20 is optimal. Primary radiological lesions include a mediastinal mass, usually associated with the terminal oesophagus. Spondylitis of the thoracic vertebrae is frequently found on chest radiography. Contrast radiography and computed tomography are helpful additional emerging modalities. Oesophageal endoscopy has a greater diagnostic sensitivity than radiography.

Figure 3 Embryonated Spirocerca lupi eggs on faecal flotation. (Image credit Dr. Tawin Inpankaew.)

Treatment

Treatment is challenging as adults are protected within nodules. Off-label anthelmintic regimes have been shown effective in killing adult worms and reducing the size of granulomas. These include:

  • doramectin 400 μg/kg subcutaneously every 14 days for a total of 6 treatments, followed by 20 additional monthly injections if resolution of nodules is incomplete [1].
  • oral milbemycine 0.5 mg/kg on days 0, 7 and 28 and then monthly [2].
  • topical moxidectin plus imidacloprid weekly for 19 weeks [3].

Food intake may be attempted in an upright standing position in the case of regurgitation due to megaesophagus.

Control

Monthly application of topical moxidectin plus imidacloprid is approved for use in dogs as a preventative for S. lupi infection in Europe.

Dogs should be not allowed to roam outdoors unsupervised or allowed to prey upon paratenic hosts such as rodents, lizards and frogs. For further control options, refer to General Considerations and Recommendations.

Public health considerations

None.

References

[1]  Lavy E., Aroch I., Bark H., Markovics A., Aizenberg I., Mazaki-Tovi M., Hagag A., Harrus S., Evaluation of doramectin for the treatment of experimental canine spirocercosis, Vet Parasitol. (2002) 109:65-73.

[2]  Kelly P.J., Fisher M., Lucas H., Krecek R.C., Treatment of esophageal spirocercosis with milbemycin oxime, Vet Parasitol. (2008) 156:358-360.

[3]  Austin C.M., Kok D.J., Crafford D., Schaper R., The efficacy of a topically applied imidacloprid 10 % / moxidectin 2.5 % formulation (Advocate(R), Advantage(R) Multi, Bayer) against Immature and Adult Spirocerca lupi worms in experimentally infected dogs, Parasitol Res. (2013) 112 Suppl 1:91-108.