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There has been a lot of publicity about the dangers of lungworm to dogs. There are no non-prescription medicines available to help control this type of lungworm, but dog owners might ask you about lungworm and you can help dog owners understand the facts about lungworm and advise them about getting further advice. By the end of this module you will:

  • know how dogs can get this type of lungworm infection
  • know how it can affect dogs
  • understand how it might be spreading in the UK
  • understand the need to refer dog owners to a vet for advice about prevention.

The lungworm Angiostrongylus vasorum (pronounced anjio-strong-gill-us vase-or- um) is one of the five main parasites that can affect dogs in the UK (the other four being roundworm, fleas, ticks and tapeworm). 

A. vasorum is a parasitic worm that lives in the heart and in the blood vessels in the lungs of dogs. Although A. vasorum is known as lungworm (because infection commonly causes breathing problems), strictly speaking it is a heartworm. It is also known as ‘French heartworm’ because the parasite was first isolated in France. Dogs infected with this lungworm can become severely ill and even die. 

Crenosoma vulpis (also known as the fox lungworm) and Oslerus osleri (also known as lungworm) are other parasitic lungworms that can affect dogs in the UK. These are ‘true’ lungworms because they live in the lungs of infected dogs. In the UK these are considered less important internal parasites in dogs than roundworm, tapeworm or the lungworm A. vasorum.

A. vasorum has a complex lifecycle that involves slugs and snails. Dogs become infected when they eat slugs and snails infected with the larvae (immature forms) of A. vasorum.  It is not know if dogs can become infected through contact with slug or snail faeces or slime trails.

  • Immature forms of the worm (called larvae) live in slugs and snails.
  • Infected slugs or snails might be eaten by dogs, foxes or frogs and toads.
  • In the dog, the larvae penetrate the intestines and spread to the heart and lungs.
  • In the heart and lungs of dogs the larvae develop into adult worms and lay eggs.
  • The eggs are coughed up, swallowed, and end up in the dog's faeces. 
  • Eggs in faeces develop into larvae, which penetrate the foot of passing slugs and snails.
  • This means that leaving dog faeces in the environment can help spread lungworm and is another important reason why people should pick up after their dog.
  • Dogs can also be infected with lungworm if they eat infected frogs or toads.

Infection with A. vasorum can cause a wide range of effects in dogs. The illness caused by A. vasorum infection is called angiostrongylosis. The speed of development and severity of the illness depends on the number of worms infecting the dog and the age and general health of the dog.  Illness usually develops slowly and subtly, which is why it can go undetected for a long time and can be difficult to diagnose. The dog might have a cough, difficulty breathing, a lack of appetite and lose weight. The infection can also affect blood clotting in the dog and so there may be blood in the faeces, or prolonged bleeding after minor injuries. Occasionally infection causes sudden death. 

This parasite is growing in importance because it appears to be spreading throughout the UK.  It is thought to have first reached Great Britain in the mid 1970s via a greyhound imported from Ireland. At first, it was only found in parts of the south of England and Wales, but it is now being found in northern England and Scotland.

Three main factors are thought to be contributing to the spread:

  • the growing urbanisation of foxes (the main carrier of the parasite);
  • warmer and wetter winters, allowing more slugs and snails to survive;
  • a rise in the movement of dogs around the UK.

Reports of cases of lungworm in dogs can suggest that it is present in the area. However increased awareness of the disease might make it more likely that cases are diagnosed. Therefore absence of reported cases in an area cannot be taken as proof that there is no lungworm in that area.

Once the disease has been correctly diagnosed by a vet, it is treatable with appropriate therapy, which must be used promptly. 

Certain worming medicines can be used to disrupt the lifecycle of A. vasorum. This helps reduce environmental contamination with infective larvae and prevents the development of disease in the dog.

Only certain prescription-only medicines (POM-Vs) are licensed to prevent lungworm. They are tablets containing the drug milbemycin or spot-ons containing moxidectin. Milbemycin and moxidectin are similar drugs belonging to the class of parasiticides called macrocyclic lactones. These drugs are also active against roundworm. Products containing these drugs contain a second drug, either one that is active against fleas, or active against tapeworm, and so the products provide broad parasite cover. 

Certain non-prescription wormers containing fenbendazole (the brands Granofen and Panacur) are licensed for the treatment of dogs infected with the lungworm Oslerus osleri. These are not suitable for controlling A. vasorum.

Dog owners should discuss with the vet whether there is a need to use preventive therapy. If a dog is judged to be at high risk of infection, it might be reasonable to use regular preventive therapy. If there is little risk of infection, regular preventive therapy might be considered unnecessary. To judge the risk the vet will consider:

  • aspects of the dog’s lifestyle that might bring it into contact with slugs and snails, and frogs and toads. For example, how much time the dog spends outdoors and whether it hunts, or eats slugs or snails, or grass that might contain these.
  • likelihood of travel, especially to areas where the parasite is known to be present.

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