Angiostrongylus vasorum

Synopsis

CAPC Recommends

• Early diagnosis is essential, if left untreated, infections could be fatal.
• The most effective way to diagnose Angiostrongylus vasorum is collection of first stage larvae in feces using a Baermann technique or serum antigen test.
• Limiting the exposure to the intermediate host (gastropod) and foxes or other wild canids (main reservoir hosts) will help prevent infections.

Species

Canine

Angiostrongylus vasorum – French heartworm.

Angiostrongylus vasorum is a parasite of foxes and other canids that also finds its way into dogs.

Overview of the Life Cycle

• Canids acquire infections by the ingestion of gastropod intermediate hosts. Gastropods eat the first-stage larvae while feeding on the feces of infected canids.
• In addition to infection though the ingestion of snails, dogs can also be infected by ingesting frog paratenic hosts.
• When the third-stage larvae in the snail or frog are eaten by the dog, they penetrate the gut wall and develop in abdominal lymph nodes before entering the portal circulation and moving to the pulmonary arteries and right ventricle. In the lungs, the worms mature, mate, and produce eggs that lodge and develop in capillaries. Larvae that hatch from the eggs move into an airspace, are coughed up and swallowed to be passed in the feces. The prepatent period is about 28 to 108 days.

Stages

• Adult Ang. vasorum are slender pinkish worms approximately 14 to 20 mm in length. The males are bursate, and the females have a “barber pole” appearance from the red intestine intertwined with the white reproductive tract.
• Larvated eggs hatch and first-stage larvae are 310 to 400 μm long with anterior cephalic buttons and tails with a dorsal spine.

Disease

• Disease due to Ang. vasorum is an inflammatory reaction with the subsequent involvement of the surrounding lung tissue that may be accompanied by interstitial pneumonia, emphysema, thromboarteritis, coagulopathis, anemia, melena, hemoptysis, and congestive right heart failure.
• Aberrant migrations of adults (eye, left ventricle, femoral artery) and first-stage larvae (brain, spinal cord, eye, kidney, liver, skeletal muscle, intestine, stomach, pancreas, spleen, adrenal gland, thyroid gland) have occurred.

Prevalence

• Angiostrongylus vasorum is mainly a parasite of continental Europe, Africa, and South America, but it has recently entered England and Ireland and has been found in the Atlantic provinces of Canada.

Host Associations – Transmission between Hosts

• This is a parasite of mainly foxes, and other wild canids, and dogs.
• Transmission requires the ingestion of an intermediate host, mollusks.
• Frogs have been shown to serve as paratenic hosts.

Prepatent Period – Environmental Factors

• The prepatent period is 28-108 days.

Site of Infection – Pathogenesis

• The adults of Ang. vasorum live in the pulmonary arteries. Infections are associated with chronic cough, dyspnea, exercise intolerance, and anorexia; gagging and weight loss are the most common clinical signs of infection.
• Pulmonary hemorrhage can occur as larvae migrate into airspaces. Granulomas develop in response to eggs and larvae, and fibrosis occurs.
• Pulmonary vascular lesions include thromboarteritis and intimal proliferation; pulmonary hypertension can lead to congestive right heart failure.

Diagnosis

• For Ang. vasorum, larvae are detected in feces using the Baermann technique or fecal flotation. Larvae are less reliably detected on fecal flotation. Multiple fecal samples may need to be examined.
• Radiographic changes may include diffuse peribronchial, interstitial and alveolar densities. Multiple nodular-like densities may occur in the peripheral regions of the caudal lung lobes, and enlargement of the right heart and pulmonary artery may also be visible.
• Serum antigen tests are commercially available to aid with diagnosis.
• qPCR on bronchoalveolar lavage samples may also be helpful.

Treatment

• Angiostrongylus vasorum has been treated with levamisole, fenbendazole, ivermectin, milbemycin oxime, and moxidectin.
• Severe dyspnea and ascites may be seen after treatment; bronchodilators, expectorants, and diuretics may be required to manage these post-treatment reactions.

Control and Prevention

• For dogs and cats, routine preventives are probably not protective against these parasites.
• Pets can be protected by minimizing the amount of hunting that the animals do.
• Fencing and mollusk control could also help to minimize the infection in dogs.

Public Health Considerations

• No human health hazard appears to be associated with Angiostrongylus vasorum.

Selected References

• Becskei C, Thys M, Doherty P, Mahabir S. Efficacy of orally administered combination of moxidectin, sarolaner and pyrantel (Simparica Trio™) for the prevention of experimental Angiostrongyus vasorum infection in dogs. Parasites and Vectors 13:64; 2020.
• Bowman DD. Georgis’ Parasitology for Veterinarians. 11ed. Elsevier. 2021.
• Morgan E, Shaw S. Angiostrongylus vasorum infection in dogs: continuing spread and developments in diagnosis and treatment. Journal of Small Animal Practice 51: 616-621; 2010.
• Schnyder M, Fahrion A, Ossent P, Kohler L, Webster P, Heine J, Deplazes P. Larvicidal effect of imidacloprid/moxidectin spot-on solution in dogs experimentally inoculated with Angiostrongylus vasorum. Veterinary Parasitology 166: 326-332; 2009.
• Willesen JL, Kristensen at, Jensen AL, Heine J, Koch. Efficacy and safety of imidacloprid/moxidectin spot-on solution and fenbendazole in the treatment of dogs naturally infected with Angiostrongylus vasorum (Baillet, 1866). Veterinary Parasitology 147: 258-264; 2007