Definition/Overview/Etiology

The nematode worm Angiostrongylus vasorum, also called French heartworm, is causing an emerging disease (Parasitic bronchopneumopathy, angiostrongylosis or French heartworm disease), with reported increase in both distribution and incidence in America, the United Kingdom, Europe, and South Africa, and Canada.^1-4 The expanding geographic range might be related to the influence of the climate on parasite distribution.

The worm infects dogs and foxes and is spread through ingestion of intermediate hosts, including slugs and snails, harboring infective third stage larvae. The adult parasites live in the pulmonary arteries and the right ventricle of the heart. The prepatent period is 40–60 days.

Respiratory disease results from the inflammatory response induced by migration of the larvae, causing granulomatous pneumonia and probably thrombotic disease.

Clinical Presentation

Infection seems more common in outdoor, young dogs, especially those playing with/eating slugs. Dogs are presented for a combination of signs including cough, exercise intolerance, respiratory distress, coagulopathy (hemoptysis, bleedings), lameness, neurologic signs, and syncope. However, clinical signs may be variable and range from subtle and chronic to more acute and severe. Here we’ll focus on patients presenting with respiratory symptoms as the main complaints.

Diagnosis

Angiostrongylosis now needs to be considered in the differential diagnosis in all chronic coughing dogs, especially in young animals possibly in contact with slugs or snails. Eosinophilia, thrombocytopenia, and hyperglobulinemia are relatively common. Thoracic radiographs generally show an interstitial and/or alveolar pattern, best present in the dorsocaudal lung fields. Definitive parasitologic diagnosis relies on observation of first-stage larvae (L1) in the respiratory tract or feces, using the Baermann test. L1 are sometimes observed on airway cytology. A major limitation of the Baermann test is that L1 excretion appears to be intermittent, and infected dogs might be negative on fecal examination. A single Baermann test is likely to detect at most 50% of infected dogs, although sensitivity can be increased by serial examination (e.g., of samples collected 3 days in succession, which is not always practical). Improved diagnostic tests are emerging. Newly developed commercial tests targeting circulating A. vasorum antigens are now available and make possible the in-clinic diagnosis of this infection.⁵ Serologic ELISA tests to detect host antibodies to the parasite have also been developed for mass-screening in different canine populations.⁶ Parasite proteins or DNA can be detected in blood or BAL fluid using sandwich ELISA or PCR, respectively.^7,8 However, there is some variability in the results obtained from different diagnostic tools which has not yet been totally elucidated.

Management

Fenbendazole (25–50 mg/kg PO q24h for 7–21 days) has been the most commonly used anthelminthic drug during the last decade. Milbemycin oxime and moxidectin both prevent establishment of adult parasites when given during the prepatent period, and substantially reduce worm burdens. However, continued monitoring after treatment is advisable, with repeated treatment as necessary. Depending on the severity of clinical signs, additional therapy with corticosteroids, IV fluid support, and oxygen can be required.

Prognosis

Dogs carrying a low worm burden may remain subclinical. The prognosis is guarded in those animals with severe respiratory signs. The disease can be fatal if left untreated.

References

1.  Gallagher B, Brennan SF, Zarelli M, Mooney CT. Geographical, clinical, clinicopathological and radiographic features of canine angiostrongylosis in Irish dogs: a retrospective study. Ir Vet J. 2012;65(1):5.

2.  Helm JR, Morgan ER, Jackson MW, Wotton P, Bell R. Canine angiostrongylosis: an emerging disease in Europe. J Vet Emerg Crit Care (San Antonio). 2010;20(1):98–109.

3.  Conboy GA. Canine angiostrongylosis: the French heartworm: an emerging threat in North America. Vet Parasitol. 2011;176(4):382–389.

4.  Lempereur L, Martinelle L, Marechal F, Bayrou C, Dalemans AC, Schnyder M, et al. Prevalence of Angiostrongylus vasorum in southern Belgium, a coprological and serological survey. Parasit Vectors. 2016;9(1):533.

5.  Schnyder M, Stebler K, Naucke TJ, Lorentz S, Deplazes P. Evaluation of a rapid device for serological in-clinic diagnosis of canine angiostrongylosis. Parasit Vectors. 2014;7(1):72.

6.  Schnyder M, Schaper R, Bilbrough G, Morgan ER, Deplazes P. Seroepidemiological survey for canine angiostrongylosis in dogs from Germany and the UK using combined detection of Angiostrongylus vasorum antigen and specific antibodies. Parasitology. 2013;140(11):1442–1450.

7.  Schnyder M, Tanner I, Webster P, Barutzki D, Deplazes P. An ELISA for sensitive and specific detection of circulating antigen of Angiostrongylus vasorum in serum samples of naturally and experimentally infected dogs. Vet Parasitol. 2011;179(1–3):152–158.

8.  Canonne A-M, Roels E, Caron Y, Losson B, Bolen G, Peters I, et al. Detection of Angiostrongylus vasorum by quantitative PCR in bronchoalveolar lavage fluid in Belgian dogs. J Small Anim Pract. 2016;57(3):130–134.