Angiostrongylus spp

From Dog
Larval stage of Angiostrongylus vasorum nematode[1]
A. vasorum in the heart of a dog[2]
A hematoma in the cerebrum of a dog, caused by A. vasorum[3]
Widespread mixed alveolar-interstitial lung pattern in a dog infected with A. vasorum[4]

Angiostrongylus spp (French heartworm) are a zoonotic parasitic nematode of dogs, endemic in the Americas, Europe, the Asia-Pacific and Africa[3].

Species which are pathogenic to dogs include:

  • Angiostrongylus vasorum
  • Angiostrongylus cantonensis (rat lungworm)

The life cycle of this parasite is similar to Aelurostrongylus abstrusus, involving a gastropod (mollusc) intermediate host. Encysted infective larvae are ingested by dogs that eat paratenic hosts such as snails. Following ingestion, the larvae migrate to visceral lymph nodes where they molt to adult worms before making their way into the lungs and pulmonary arteries[5].

A. cantonensis shows obligate neurotropism, i.e. larvae must migrate through the central nervous system (CNS) before taking up residence in the pulmonary arteries[6]. These larvae of A. cantonensis can be seen in the CNS within hours to days following ingestion[7]. Autochthonous A. vasorum infections have also been reported, but only in Canada[8].

These lungworms were first reported in foxes, which are the natural definitive host but have since been diagnosed in dogs.

It seems unlikely that the role of endosymbiontic alphaproteobacteria such as Wolbachia spp play a role in the development and reproduction of this parasite[9].

Angiostrongylosis is considered to be a disease of primarily young animals.

Clinical signs associated with A. vasorum are related to right-sided heart failure and include malaise, coughing, dyspnea, anemia, pulmonary hypertension[10] and pneumonia. Death may ensue with severe infestations, primarily due to a DIC-related systemic coagulopathy[11] and consequential acute respiratory distress syndrome.

Hemoperitoneum[12], hemothorax[13] and intracranial hemorrhage[14][15] have also been reported due to visceral migration, with secondary meningitis and encephalomyelopathy due to intracranial migration[16]. Immune-mediated thrombocytopenia has also been observed[4].

A separate, characteristic, syndrome has been described with A. cantonensis consisting of hind limb paresis, lumbar hyperaesthesia and urinary incontinence[17]. Some dogs develop additional signs such as hemoptysis[18], scleral hemorrhage, forelimb paresis, cranial nerve palsies, altered mentation, coma and seizures.

Diagnosis is based on presenting clinical signs, evidence of tracheobronchial fluid or fecal larvae (using Baermann technique[19]) and ELISA serology[20]. PCR assays can be used to speciate the particular parasite involved[21].

A differential diagnosis would include other cardiopulmonary parasites such as Aelurostrongylus abstrusus, Eucoleus aerophilus, Crenosoma vulpis and Dirofilaria immitis. Signs of progressive meningo-encephalomyelopathy are seen with a number of other diseases, including distemper, neosporosis, toxoplasmosis, cryptococcosis and other fungal diseases such as Blastomyces spp.

Treatment of active angiostrongyliasis can be difficult. The use of anthelmintics may worsen the clinical symptoms due to exacerbated release of metazoan antigens from dying worms[17]. However, concurrent use of corticosteroids (e.g. prednisolone) or other immune modulators (e.g. cyclosporin) may ameliorate this complicating issue.

Recommended drugs are fenbendazole (50 mg/kg PO q 24 hours for 5-35 days) or ivermectin in incrementally increasing daily doses for 4 - 6 weeks. The prognosis of angiostrongyliasis should be considered guarded when complicated by haemostatic dysfunction and even more so when the condition gives rise to severe neurological deficits[3].

Preventative therapy is effective with selamectin, doramectin and ivermectin, given on a monthly basis.

Acquired immunity appears to be short lived or incapable of preventing re-infection.

References

  1. Traversa D et al (2010) Canine and feline cardiopulmonary parasitic nematodes in Europe: emerging and underestimated. Parasit Vectors 3:62
  2. Gallagher B et al (2012) Geographical, clinical, clinicopathological and radiographic features of canine angiostrongylosis in Irish dogs: a retrospective study. Ir Vet J 65(1):5
  3. 3.0 3.1 3.2 Gredal H et al (2011) Acute neurological signs as the predominant clinical manifestation in four dogs with Angiostrongylus vasorum infections in Denmark. Acta Vet Scand 53:43
  4. 4.0 4.1 Jo'neill E et al (2010) Immune-mediated thrombocytopenia associated with angiostrongylus vasorum infection in a Jack Russell terrier. Ir Vet J 63(7):434-440
  5. Bowman, DD (2009) Georgis' parasitology for veterinarians. 9th edn. Elsevier Saunders, Missouri. pp:187-188
  6. Lunn JA et al (2012) Twenty two cases of canine neural angiostronglyosis in eastern Australia (2002-2005) and a review of the literature. Parasit Vectors 5:70
  7. Bhaibulaya M (1975) Comparative studies on the life history of Angiostrongylus mackerrasae Bhaibulaya, 1968 and Angiostrongylus cantonensis (Chen, 1935). Int J Parasitol 5:7–20
  8. Conboy GA (2011) Canine angiostrongylosis: the French heartworm: an emerging threat in North America. Vet Parasitol 176(4):382-389
  9. Foster JM et al (2008) Absence of Wolbachia endobacteria in the non-filariid nematodes Angiostrongylus cantonensis and A. costaricensis. Parasit Vectors 1(1):31
  10. Matos JM et al (2012) Recruitment of arteriovenous pulmonary shunts may attenuate the development of pulmonary hypertension in dogs experimentally infected with Angiostrongylus vasorum. J Vet Cardiol 14(2):313-322
  11. Cury MC et al(2002) Hematological and coagulation profiles in dogs experimentally infected with Angiostrongylus vasorum (Baillet, 1866). Vet Parasitol 104:139–149
  12. Hirst C & Adamantos S (2012) Autologous blood transfusion following red blood cell salvage for the management of blood loss in 3 dogs with hemoperitoneum. J Vet Emerg Crit Care (San Antonio) 22(3):355-360
  13. Mozzer LR & Lima WS (2012) Rupture of the thoracic aorta associated with experimental Angiostrongylus vasorum infection in a dog. Parasite 19(2):189-191
  14. Zarelli M et al (2012) Imaging diagnosis: CT findings in a dog with intracranial hemorrhage secondary to angiostrongylosis. Vet Radiol Ultrasound 53(4):420-423
  15. Lowrie M et al (2012) Concurrent medical conditions and long-term outcome in dogs with nontraumatic intracranial hemorrhage. Vet Radiol Ultrasound 53(4):381-388
  16. Summers BA et al (1995). In: Inflammatory disease of the central nervous system. In Veterinary Neuropathology. 1. Duncan L, editor. St Louis: Mosby. pp:159–170
  17. 17.0 17.1 Mason KV (1983) Naturally acquired Angiostrongylus cantonensis infection: A cause of ascending paralysis of dogs in the Brisbane area. Master of Veterinary Science thesis: University of Queensland, Department of Veterinary Medicine
  18. Glaus T et al (2010) Natural infection with Angiostrongylus vasorum: characterisation of 3 dogs with pulmonary hypertension. Schweiz Arch Tierheilkd 152(7):331-338
  19. Schnyder M et al (2011) Comparison of faecal techniques including FLOTAC for copromicroscopic detection of first stage larvae of Angiostrongylus vasorum. Parasitol Res 109(1):63-69
  20. Schnyder M et al (2011) An ELISA for sensitive and specific detection of circulating antigen of Angiostrongylus vasorum in serum samples of naturally and experimentally infected dogs. Vet Parasitol 179(1-3):152-158
  21. Al-Sabi MN et al (2010) PCR detection of Angiostrongylus vasorum in faecal samples of dogs and foxes. Parasitol Res 107(1):135-140