Angiostrongylosis

Also known as:	French Heartworm Lungworm
Do not confuse with:	Heartworm caused by Dirofilaria immitis

Description

Angiostrongylosis is a clinical syndrome caused by infection with Angiostrongylus vasorum, the 'French heartworm' or 'lungworm'. The adult worms accumulate in the pulmonary arterial vessels and right heart chambers and release eggs and larvae into the circulation. The adult worms obstruct blood flow through the pulmonary circulation and lead to the development of pulmonary undercirculation, right ventricular hypertrophy and cor pulmonale. The adults also cause local inflammation of the pulmonary arteries and thrombi are able to form against the inflamed vessel wall.

The eggs lodge in the small pulmonary capillaries and the L1 larvae hatch at this location. These larvae penetrate the capillaries and enter the pulmonary parenchyma to cause an interstitial pneumonia. This pneumonia is the major cause of the respiratory signs observed in infested animals but, in severely affected animals, pulmonary oedema may also develop. By an unknown mechanism, the presence of infection reduces the blood concentrations of factors V and VIII and causes thrombocytopathia and thrombocytopaenia. Affected animals therefore often suffer from some form of coagulopathy.

• Gross:
  • Patchy white appearance with haemorrhagic areas within
• Microscopically:
  • Golden pigment within macrophages (haemosiderin)
  • Inflammation and scarring of alveolar walls -> enlargement of remaining air spaces

pulmonary thromboembolism

Signalment

The lungworm is acquired when dogs eat slugs and snails infected the the L3 larvae. It is therefore crucial to establish whether the dog does eat slugs or snails. As foxes are also able to act as definitive hosts, areas with a dense population of foxes are likely to have a high lungworm prevalence. A. vasorum was traditionally considered to be a disease acquired by animals that had travelled to Europe but it is now being diagnosed in untravelled animals as far north in the UK as Scotland.

Diagnosis

Clinical Signs

Clinical signs are mainly related to coagulopathies and the presence of worms, eggs and larvae in the pulmonary vasculature and parenchyma. They include:

• Coagulopathies
  • Cutaneous bruising or intra-cavitatory haemorrhage. Haematomas may form in any location including the spinal cord.
• Pulmonary disease
• Cardiovascular disease

The results of a recent study indicate that the most common clinical signs observed in infected dogs are cough (65%), dyspnoea (43%), coagulopathy (35%) and collapse (26%).

Laboratory Tests

Eosinophilia.

Diagnostic Imaging

Lung pattern.

Other Tests

The gold standard test is considered to be identification of L1 larvae in faeces. At least five faecal samples should be submitted by examination by the Baermann technique as excretion of the larvae is variable.

Treatment

Infection with Angiostrongylus vasorum may be treated easily with suitable anthelmintics. Ideally, four 5 day courses of a benzimidazole should be administered at a high dose rate over 1-2 months. Fenbendazole is widely available in the UK in a granule form and this is used most frequently in the treatment of A. vasorum. If infection is suspected but larvae cannot be detected in faeces, it may still be worth treating the animal.

Prevention

With increasing awareness of the threat posed by A. vasorum and as the parasite spreads across the UK, preventative treatment is now used more widely. Suitable products include: