Behind the pretty name hides a serious threat to the health of our beloved dogs. Angiostrongylus vasorum is also known as ‘French heart worm’. Luckily, it’s often treatable, and preventive treatment is widely used, nonetheless it’s a parasite everyone should know and be aware off – especially owners who are frequent visitors to dog parks, like the ones where I take my own dogs.
Angiostrstrongylus vasorum, or the French heartworm, is a parasite with a bursa, and only around 14-24mm long. It belongs to an order of parasites called Nematodes, and is dependent on a moist environment to survive. In live worms a barbers-pole like intestines can be seen within the worm – also pictured below. L1 larvae are released from the first host animal along with faeces. The first host will often be other dogs, but foxes are also common. Here from they are eaten by snails, and the worm place itself in the mucosal tissue. Within the snails, they develop into L3 larvae’s. The L3 is transferred to dogs when these eat the snails. Within the dog the L3 migrates through the lymphatic systems to the right heart ventricles and A. Pulmonalis where they attach themselves to the walls of the bloodwessels. Within the artery or heart ventricle the, now adult, worms will lay their eggs. The adult worm will often obstruct blood flow, which can lead to pulmonary under-circulation, the worms will also secrete anticoagulant, which can cause excessive bleeding. The released eggs will also lodge themselves in the pulmonary capillaries and hatch, where after the L1 larvae’s will penetrate the alveoli and enter the pulmonary circulation, which can cause respiratory symptoms like pneumonia.
Clinical signs are mainly related to the presence of the worms secreting anticoagulant, and the eggs and larvae in the pulmonary system. Acute symptoms are, amongst others: Coughing, dyspnoea bleeding within the mucosa, and increased respiration frequency. In extreme cases, other symptoms sudden collapsing, or right-sided congestive heart-failure. Besides the clinical symptoms, other tests will also be needed to give a diagnose. The most commonly of these diagnostic techniques used, is the Baermann technique which examines whether larvae are present in the faeces of the dogs. How many samples of faeces that are needed varies from country to country; in Denmark, the normal amount is 3 separate samples collected over 3 days. The reason for this is, that the number of larvae in the faeces can vary from day to day.
Treatment varies depending on the severity of the symptoms, but oxygen should be administered in cases of severe dyspnoea and thereafter medicine should be prescribed to treat the infection. In the end, treatment should always be based on the individual animal. Luckily, preventive treatment has become more common. In Denmark puppies should always be given worm-treatment before leaving the breeder, and this should be kept up by the future owners. Otherwise owners should also be aware of high-risk areas, like dog parks and other places where many dogs are around. This is due to one dog being infected and defecating in a different area, can cause the larvae to spread to many new snails, and thereby infecting more animals. This is also why some veterinarian advise to have a Baermann faeces test done once a year, to ensure a happy and healthy animal. In the end, Infections with the heartworm can cause severe illness, but often when cleared, the dogs suffer few adverse consequences.