Lungworm and heartworm are different parasites. Both can cause serious illness, but they are contracted in different ways and require different prevention and treatment.
Lungworm is present in the UK. Heartworm is not considered endemic in the UK and is primarily a concern for dogs that have lived in or travelled to affected countries.
Lungworm
The name “lungworm” can refer to several parasites, but the most serious one commonly discussed in UK dogs is Angiostrongylus vasorum. It is sometimes called French heartworm because the adult worms live in the pulmonary arteries and the right side of the heart.
Lungworm can affect the lungs, circulation, blood clotting and nervous system. Severe infections can be fatal.
Contact a veterinary surgeon immediately if your dog is struggling to breathe, collapses, has a seizure or develops unexplained bleeding.
How dogs become infected
Dogs become infected by swallowing an infected slug or snail. This may happen deliberately, but more often occurs accidentally while a dog:
- Eats grass, soil or something found outdoors.
- Drinks from an outdoor bowl or puddle.
- Plays with a toy that has been left outside.
- Scavenges or eats a frog that has carried the parasite.
Slime trails are often mentioned as a possible source of exposure, but swallowing an infected slug or snail is the established principal route of infection.
Dogs do not normally pass lungworm directly to another dog. Infected dogs pass larvae in their faeces. Slugs and snails become infected, and the life cycle continues when another dog swallows them.
Possible symptoms
Symptoms vary considerably and can resemble other illnesses. They may include:
- Coughing.
- Fast, heavy or difficult breathing.
- Reduced stamina or reluctance to exercise.
- Lethargy, weakness or weight loss.
- Loss of appetite.
- Vomiting or diarrhoea.
- Unexplained bruising or bleeding.
- Bleeding from the nose or gums.
- Blood in the urine or faeces.
- Pale gums.
- Poor wound healing.
- Changes in behaviour, weakness, seizures or collapse.
A dog does not have to show every symptom. Some dogs initially have only a mild cough or appear slightly off colour before becoming seriously ill.
Diagnosis
A veterinary surgeon may use one or more of the following:
- A physical examination and detailed history.
- A blood test for lungworm antigen.
- Examination of faecal samples using a specialist technique.
- Blood tests to assess anaemia, clotting and organ function.
- Chest X-rays or other imaging.
- Examination of fluid or samples from the airways in selected cases.
No single test is perfect in every stage of infection. If lungworm remains strongly suspected, the veterinary surgeon may recommend repeat or additional testing.
Treatment
Lungworm is treated using an appropriate veterinary worming medicine. The treatment and level of monitoring depend upon how ill the dog is.
A severely affected dog may require hospitalisation, oxygen, intravenous fluids, treatment for bleeding or seizures and, occasionally, a blood transfusion.
Killing a heavy burden of worms can itself cause complications, so a dog with suspected or confirmed lungworm should be treated under veterinary supervision.
Prevention and individual risk
Licensed prescription products are available in the UK to prevent Angiostrongylus vasorum. However, not every general worming product covers lungworm.
The appropriate approach should be discussed with a veterinary surgeon and based upon the individual dog’s lifestyle, location and exposure. Factors that may increase risk include eating grass, hunting, scavenging, chewing outdoor toys and living in an area where lungworm is known to occur.
Collielife does not suggest that every breeder or owner routinely worms every dog every month without considering whether there is a need.
Some owners use parasite testing or less frequent treatment for intestinal worms. However, a worm count is not automatically a substitute for lungworm prevention, and the intervals required for a licensed lungworm product may differ from an owner’s normal six-monthly worming routine.
Discuss the benefits and disadvantages of testing and preventative treatment with your own veterinary surgeon. Only use a product specifically licensed for the parasites that need to be covered.
Reducing exposure
- Do not leave food bowls, chews and toys outside overnight.
- Wash outdoor bowls and items contaminated by slugs, snails or slime.
- Prevent scavenging where possible.
- Collect dog faeces promptly.
- Do not deliberately use slug pellets where dogs could encounter them; many are poisonous.
- Ask your veterinary practice whether lungworm has been diagnosed locally.
Heartworm
Canine heartworm disease is caused by Dirofilaria immitis. It is transmitted through the bite of an infected mosquito.
Heartworm is not considered endemic in the UK. Cases diagnosed here usually involve dogs that have travelled abroad or been imported from a country where the parasite occurs.
Heartworm is established in many parts of the world, including areas of the United States and southern and eastern Europe.
Speak to your veterinary practice well before travelling with your dog. The parasite risks and recommended treatments depend upon the countries being visited, the season and the length of the trip.
The legal pet-travel requirements do not necessarily protect a dog against heartworm or every other parasite present overseas.
How heartworm is transmitted
A mosquito becomes infected when it feeds on an infected animal carrying immature heartworms in its bloodstream. The parasite develops inside the mosquito and can be passed to another dog when the mosquito feeds again.
Once inside a dog, the larvae develop over several months. Adult worms live mainly in the pulmonary arteries and may also extend into the heart. They can damage the lungs, blood vessels and heart.
Heartworm is not transmitted directly from one dog to another. A mosquito is required to complete transmission.
Possible symptoms
Dogs may show no obvious symptoms during the early stages. As the infection progresses, symptoms may include:
- A persistent, often dry cough.
- Reduced stamina and becoming tired during exercise.
- Fast or difficult breathing.
- Weakness or lethargy.
- Reduced appetite and weight loss.
- Fainting or collapse.
- A swollen abdomen caused by fluid accumulation.
- Heart failure in advanced cases.
Heartworm can cause permanent damage before symptoms become obvious. Tell your veterinary surgeon if your dog has previously lived in or travelled to a country where heartworm occurs, even if the journey took place months or years earlier.
Diagnosis and treatment
Diagnosis may involve antigen testing, examination of the blood for immature worms, chest X-rays, ultrasound or heart scans and other blood tests.
Treatment of an established infection is complex and carries risks because dead or dying worms can obstruct blood vessels in the lungs. Treatment must be planned and supervised by a veterinary surgeon.
Strict exercise restriction is often an important part of treatment. Surgery may occasionally be required in very severe cases.
Preventing heartworm during travel
Preventative medicines kill immature stages before they develop into adult heartworms. The timing of treatment is important and depends upon the product and destination.
A veterinary surgeon may also recommend protection against mosquito bites and tests before or after travel. Do not wait until the dog returns to the UK before seeking advice.
Fred’s lungworm story
The following account was sent to Collielife by Sue Phipps of Oakanmoor Rough Collies. It describes Fred’s symptoms, diagnosis and recovery from lungworm.
This is one owner’s experience. Treatment for another dog may be different and must be directed by its veterinary surgeon.
Fred initially began coughing occasionally. It mostly happened when he drank water, it was not continuous and he otherwise seemed well.
When the cough had not improved by the following day, I wondered whether he had kennel cough. He had not knowingly been in contact with other dogs because this occurred during the Covid restrictions, so I thought that was unlikely. To be safe, I made a veterinary appointment for the following day.
By then things had changed. Fred’s breathing had become very laboured and the cough was worse.
I had also arranged routine blood tests because he was due to have a tooth extracted and I wanted to ensure everything was functioning normally.
The veterinary surgeon agreed that Fred’s breathing was very laboured. His heart was beating rapidly and his temperature was raised. Because he had a high temperature, the vet gave him an antibiotic injection while we waited for the blood results.
I took Fred home, but overnight his breathing and cough worsened. He would not eat and became very lethargic, so we returned to the veterinary practice.
The initial blood results were satisfactory, although the cardiac blood result would take another couple of days. At this stage, I was seriously concerned that Fred had a heart problem.
Fred continued to deteriorate and his breathing became extremely laboured. I kept the veterinary surgeon informed. The vet suggested treating for worms because some parasites can cause respiratory problems.
I regularly treated my dogs for worms, but the product I used did not cover lungworm. The vet also requested a lungworm blood test and explained that the practice had not previously recorded a positive result in approximately 20 years.
The practice contacted me that evening to say that Fred’s lungworm test was positive. I collected the prescribed treatment immediately.
Fred did not improve straight away. He was given further medication for possible secondary infection and additional supportive treatment because he was not eating. His cardiac blood results were normal, which surprised us because his breathing remained so laboured.
I am pleased to say that Fred gradually began to improve, although his recovery was slow.
I wanted to share Fred’s story as a reminder that lungworm can be extremely serious. My dogs did not deliberately eat slugs, and I believed that their usual worming treatment protected them. I discovered that the product did not include lungworm cover.
Please check exactly which parasites your dog’s treatment covers and discuss your individual dog’s risk with your veterinary surgeon. A cough, breathing difficulty or unexplained bleeding should never be ignored.
Sue Phipps
Oakanmoor Rough Collies
Further information
ESCCAP UK – lungworm infection and individual risk
Companion Animal Parasite Council – Angiostrongylus vasorum
UK Government – imported diseases including heartworm
ESCCAP – parasite advice for dogs travelling in Europe
Veterinary disclaimer: This article provides general information and includes a personal account from a dog owner. It is not a substitute for veterinary diagnosis or treatment.
Seek urgent veterinary assistance if your dog has difficulty breathing, unexplained bleeding, seizures, weakness or collapse.
The parasite-prevention information on this page has been updated. Licensed prescription products are available for lungworm, but the most suitable testing or treatment programme should be discussed with your veterinary surgeon and based upon the individual dog’s risk.