Lungworm, also known as angiostrongylus vasorum, is a fairly recent addition to the collection of UK parasites affecting our pets, and is unfortunately the most serious parasitic threat to the health of dogs in the UK, as Rosie Skinner explains.
The worm infects dogs and foxes when they eat snails and other gastropods infected with larvae of angiostrongylus vasorum (also referred to as A. vasorum).
Larvae can also be ingested from when dogs drink puddle water, eat grass or play with toys left outside where slugs and snails have been on them. Angiostrongylus vasorum used to be fairly confined to certain areas of the UK – i.e. the South West and Scotland, however in recent years it has become very prevalent in the South East as well, possibly due to an increasing urban fox population and wetter weather.
At Nine Mile Vets, we have seen several distressing cases of lungworm lately and some of the cases were tragically fatal. There is a licensed preventative treatment for lungworm available on prescription so if you are concerned then you should speak to your Vet. This particular parasite mainly affects dogs, however it can rarely affect cats and cats have their own lungworm, however it is less severe than the dog version.
Lungworm Life Cycle & Disease Process
After having been ingested by the dog or fox in a snail or slug, the larvae migrate from the gut via the lymph nodes, liver, veins into the right side of the heart and finally into the pulmonary artery and lungs. The larvae then mature into adult worms in the lungs. The larvae from these adult worms migrate into the airways and up the trachea, where they are coughed up and swallowed in sputum. The larvae are then in the gut where they leave the host in faeces ready to be eaten by slugs and snails and start the process again.
See the diagram below.
1. Various snails act as an intermediate host. Infective larvae develop here (L3).
2. The fox is a natural host of Angiostrongylus vasorum, but dogs can be infected too.
3. Larvae (L3–L4–L5) migrate via the alimentary tract, abdominal lymph nodes, liver, venous system and right heart into the pulmonary artery.
4. Mature Angiostrongylus vasorum in the pulmonary artery (top female, bottom male).
5. Mature worms lay eggs which enter the lung via the bloodstream.
6. Tissue nodules (a) consisting of cellular infiltrate filled with larvae and eggs develop in the lung. Bronchiole (b) Arteriole (c).
7. Larvae (L1) develop inside the eggs in the capillaries (d), hatch (e )and move into the alveolus (f.) They are transported up the airway to the larynx and then swallowed.
8. Larvae (L1) enter the ground through faeces.
As you can see from the life-cycle, the parasite has ample opportunity to cause damage to the host’s body. The lungs are the organs most severely affected by the parasite, and infected dogs develop a severe pneumonia and usually a cough. In the simplest cases, symptoms are restricted to the lungs, but this can make the dog severely debilitated nonetheless. In more complicated cases dogs develop coagulation (blood- clotting) deficiencies.
These are life-threatening and can cause sudden death. Signs are similar to those in dogs who have eaten rat poison. Bleeding can occur into the abdomen, chest, central nervous system, gut, bladder and under the skin – pretty much anywhere. Bleeding into the central nervous system can cause seizures and neurological problems which are not always reversible. The levels of bleeding can be dramatic and rapidly fatal, especially if the dog is bleeding externally through a small cut or into the abdomen or chest cavities. The amount of bleeding that can occur through the smallest of wounds in the absence of normal clotting can be vast. It is not fully understood how the parasite causes the problems with blood clotting.
Diagnosis of this distressing parasite is made on the basis of clinical signs, the worming history of the patient, chest x-rays and examination of samples from the respiratory tract and faeces. Sometimes more than one test is required to find these worms. If your Vet suspects that your dog may have lungworm, they will treat them for it anyway as treatment is simple and effective and won’t interfere with any other treatments or tests for other possible diagnoses.
There are several treatment options for killing the lungworm parasite. Treatment is aimed at killing the parasite but some dogs will need prolonged hospitalisation, blood transfusions, oxygen therapy and other supportive care. Residual damage to the lungs can be permanent. Costs of diagnosis and treatment can soon mount up when treating this condition. Most cases do recover, especially if they have symptoms confined to the lungs, it is the dogs with clotting disorders who are the highest risk, however with appropriate and timely veterinary intervention many of these dogs can be saved.
Not all wormers are active against angiostrongylus vasorum. There is one licensed preventative which is available on prescription from your Vet. This drug should be used routinely every month and is applied as a spot-on on the back of the neck. It also kills fleas, flea larvae, intestinal roundworms, ear mites, scabies and lice. We recommend that all dogs are treated with this drug every month as there have been cases of lungworm in dogs that have only been infrequently treated with this drug.