French heartworm

Angiostrongylus vasorum, also known as French heartworm, is a species of parasitic nematode in the family Metastrongylidae. It causes the disease canine angiostrongylosis in dogs. It is not zoonotic, that is, it cannot be communicated to humans.

These nematode worms are small and pinkish in color . The length is 14.0–20.5 mm . The width is 0.170-0.306 mm .  Females have a barbers pole appearance.

Life Cycle:

The life cycle begins when L3 larvae are ingested by a definitive host, primarily the fox or dog. This can be through eating mollusc (intermediate hosts), frogs (paraentenic hosts), or from food infected with slime from the slugs or snails. The L3 larvae migrate to the mesenteric lymph nodes and moult to L4, and L5. The L5 larvae migrate through the portal circulation and through the liver and the adults end up at the pulmonary artery or right side of the heart.

The adults then mate and produce eggs. The eggs move to the alveolar capillaries via the circulation and hatch to L1 larvae. The L1 larvae burrow though the alveolar and are then coughed up and swallowed. L1 larvae are therefore passed in the faeces of infected cannids.

The L1 larvae infect intermediate hosts (primarily slugs and snails) by penetrating the foot of the mollusc and develop to L3 within.

Adult worms can live for 2 years. The pre-patent period is 6–10 weeks.

Pathology:

Pathology is from both the adult worms, eggs and larvae.

Cardio-respiratory signs are one clinical symptom. Chronic, coughing, exercise intolerance, dyspnoea and tachypnoea in young dogs is due to blood vessels being blocked by adults, eggs and larvae.

The parasite also causes coagulopathies. Haematomas and prolonged bleeding are as a result of thrombocytopaenia (where clotting factors are decreased due to them binding to antigen - antibody complexes). Clotting factors V and VIII are also reduced. Hypochromic anaemia is another symptom, also used in diagnosis and is due to the parasite interfering with haemoglobin synthesis.

Angiostrongylus vasorum also causes neurological damage. These present as ataxia, paresis, loss of vision, behavioural changes and seizures. All these symptoms are as a direct result of CNS haemorrhages.