Dogs of all ages and breed can be affected by lungworm – be aware of the causes as symptoms
Any infestation of the lower respiratory tract by parasitic worms is known as lungworm infection. Sometimes the adult parasitic worm lives within the respiratory tract or within the blood vessels of the respiratory tract. Wherever the adult lungworm lives, their eggs or larvae are released into the dog’s respiratory tract and coughed up.
Some parasitic worms have simple life cycles where the adult worms lay eggs that are coughed up and appear in saliva or may be swallowed and appear in faeces. Other dogs that ingest the eggs become infected and a larvae hatches from the egg and burrows through the bowel wall and travels back to the respiratory tract or its associated blood vessels.
Other parasitic worms have complex lifecycles which involve other host species that must be infected before another dog can become infected. In this situation the larvae are ingested by an intermediate host such as a slug, land or freshwater snails where they hatch and a larvae develops. It is when the slug or snail is eaten by a dog that the dog becomes infected.
All lungworm infections cause symptoms of respiratory disease including:
||- Shortness of breath
||- Reduced exercise tolerance
Lungworms that infest the chambers of the right side of the heart and the blood vessels of the respiratory tract can cause additional symptoms relating to their effect on the circulatory system:
- Cardiorespiratory (heart and lung), primarily a cough
– prolonged bleeding (clotting problems)
– bruising, haematomas (large blood filled blisters)
– anaemia (paleness of membranes around the eyes and gums)
– epistaxis (nose bleeds)
– bleeding into the eye
- Neurologic signs (due to larva becoming ‘lost’ and migratingthe wrong way)
– weakness, ataxia (drunken movements)
– depression, behavioural changes
– fits, blindness, and spinal pain
Common types of lungworm that can affect dogs in the UK
||Dog and slug life cycle
||Dog to dog life cycle
|Oslerus (Filaroides) osleri
||Dog to dog life cycle
Was first discovered in France and, for this reason, is commonly called French heartworm though it is found throughout Western Europe. Although it is called heartworm, it actually lives in the lung arteries of foxes and dogs. Foxes are considered to be a reservoir of infection.
Dogs become infected by eating the intermediate host: slugs, land and freshwater snails. Frogs that have eaten infected slugs and snails can also pass the infection on. Most dogs do not deliberately eat slugs and snails; this usually occurs by accident when slugs and snails crawl in food bowls or bones. Infected larvae can be released from the slug or snail in the slimy trail they leave behind. So, potentially, larvae can be found wherever slugs or snails have left their trails, such as outdoor drinking water bowls.
Slugs and snails eat the immature larvae while feeding on the faeces of infected dogs or foxes. When the developed larvae, from the slug or snail, are eaten by the dog, they penetrate the gut wall and develop in abdominal lymph nodes before entering the circulation and travelling to the right ventricle of the heart and the pulmonary arteries of the lungs.
Once in the right ventricle and pulmonary arteries, the worms mature, becoming pinkish in colour and growing to 14 to 20mm long. The male and female worms mate and produce eggs that lodge and develop in the capillaries of the lungs. Larvae hatch from these eggs and move into an airspace of the lungs. They are then coughed up and swallowed to be passed out in the dog’s faeces.
Symptoms in infected dogs depend upon the number of larvae ingested as well as the dog’s own ability to defend itself against infection, which includes its age and the presence of other existing disease conditions. Illness usually has a slow onset and is chronic in nature so it is often seen months or years after the initial infection.
Symptoms are most commonly seen in dogs less than 2 years of age. Typically symptoms include reduced exercise tolerance, laboured breathing, coughing, poor appetite, and weight loss. Acute symptoms may occur if worms become dislodged or larvae become lost and end up lodged in other parts of the body including the kidneys and brain.
Milbemycin and Moxidectin are licenced to treat Angiostrongylus vasorum infection and they do so by killing the parasite. Other drugs may be required to manage symptoms of infection. Sometimes these drugs may be required before treatment to kill the parasites but they may also be required after treatment too. The rapid killing of parasites within the dog’s body can cause severe post-treatment symptoms, which may require intensive medical treatment and hospitalisation.
Prevention of infection in the first place is a much better goal. To break Angiostrongylus vasorum’s life cycle, faeces should be promptly picked up to prevent slugs and snails from becoming infected. Control slugs and snails in the dog’s garden, kennel, and any food stores. Food bowls, water bowls, and toys should not be left outside where slugs and snails could leave infected trails over them. Foxes should be discouraged from entering an owner’s garden so owners should not leave scraps of food out. Routine worming for dogs will help prevent infection with Angiostrongylus vasorum.
The heartworm, Dirofilaria immitis, is seen in the USA and the mosquito is its intermediate host. Advocate, a spot on parasitic treatment from Bayer, contains Moxidectin; however, its product licence currently does not claim that it kills Angiostrongylus vasorum. It does claim to kill Dirofilaria immitis.
Capillaria aerophila is a parasitic lung worm of dogs and other carnivores. It inhabits almost the full length of the respiratory tract from the frontal sinuses (bony chambers within the skull that communicate with the nasal cavity), down to the airways as they divide in two to enter the lungs.
Adults are 25 to 35 mm long and the females lay eggs in the lungs, which are then coughed up, swallowed, and appear in the dogs faeces. The lifecycle is direct and dogs become infected by ingesting mature eggs that contaminate food and water. Again, foxes may be a reservoir and should be discouraged from gardens.
Ingested larvae burrow through the intestine and travel through the circulation to the lungs. 40 days after infection the parasites start to produce eggs to complete the lifecycle. Symptoms include coughing, sneezing, and nasal discharge. Treatment with a long course of fenbendazole is usually effective.
Oslerus (Filaroides) osleri
Known as tracheal worms of dogs, Oslerus (Filaroides) osleri are often found in thin-walled nodules around the bronchial bifurcation where the trachea divides into each lung. Males are about 5 mm long, and females 10-15 mm. The life cycle is direct and typically an infected bitch can transfer larvae in her saliva to her pups while licking and cleaning them. When a pup ingests the larvae it burrows through the intestine into the circulation where it is carried to the lungs and bronchi.
The most common symptom is a persistent dry cough, but a diagnosis is best made using bronchoscopy to visualise the nodules near the bronchial bifurcation. While the parasite can be killed with common wormers often the nodules require surgical excision to relieve symptoms.
Filaroides hirthi is similar to Oslerus (Filaroides) osleri but adults are found in the body of the lung as opposed to the trachea. The body creates a local reaction around these ‘nests’ containing pregnant females. Diagnosis is difficult, but the parasite is killed by extended treatment with the wormer fenbendazole. It is very rare and mainly seen in kennel dogs.
Lungworm infection can produce a range of symptoms from an anticipated cough to fits and nose bleeds. Treatment is not always simple, but prevention of infection is the logical goal.
- Worm your dog regularly following a protocol from your vet.
- Discourage foxes from your garden as they are a reservoir for many parasites.
- Don’t leave food and water bowls or toys outside.
- Manage snails and slugs but beware of using slug bait because it’s poisonous to dogs.
David Chamberlain BVetMed., MRCVS.
Veterinary Consultant to PetSafe®