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“Lungworm” is a group label, not a single disease. Several different nematodes (roundworms) are grouped under that name, and each has its own location in the body, its own route of infection, its own diagnostic test, and its own treatment evidence. A veterinarian therefore cannot confirm “lungworm” in general or apply one standard course to every dog. The workup starts with a narrower question: which parasite is most likely? The test and the treatment decision follow from that answer.
The one most owners should learn about first is Angiostrongylus vasorum, also called French heartworm, because it can be serious and early diagnosis matters most with it. The other canine lungworm-type parasites differ in where they live, how they are found, and what drugs have been studied. This article explains how each group is diagnosed and treated, what the evidence does and does not establish, and what to ask your veterinarian.
Which lungworm is being considered
The table compares the parasites most often named in veterinary parasite guidance. Use it to understand the questions your vet is working through, not to decide what your dog has.
| Parasite | Body location | How dogs acquire it | Main diagnostic method | Treatment reported in CAPC guidance |
|---|---|---|---|---|
| Angiostrongylus vasorum (French heartworm) | Pulmonary arteries and right side of the heart | Eating infective larvae in gastropods (slugs and snails); paratenic hosts such as frogs in some circumstances | Baermann examination of fresh feces, or serum antigen test | Levamisole, fenbendazole, ivermectin, milbemycin oxime, moxidectin |
| Crenosoma vulpis (fox bronchial worm) | Bronchi (airways) | Ingesting an infected mollusk; mice described as paratenic hosts | Baermann recovery of first-stage larvae from feces | Fenbendazole; milbemycin oxime/praziquantel; topical imidacloprid/moxidectin (in experimentally infected dogs) |
| Eucoleus aerophilus | Respiratory tract | Not stated (CAPC) | Eggs identified in sputum or feces | Ivermectin or benzimidazoles |
| Eucoleus boehmi | Nasal cavity and sinuses | Not stated (CAPC) | Eggs identified in nasal discharge or feces | Not stated (CAPC) |
| Filaroides species | Lung tissue | Not stated (CAPC) | Larval features and species-specific testing considerations | Several approaches described; not interchangeable |
| Angiostrongylus cantonensis (rat lungworm) | Not stated for dogs | Dogs are incidental hosts; route not stated for dogs | Fecal examination not useful in dogs | No effective treatment reported; supportive care often the only or best option |
Signs that overlap with other illness
Lungworm signs look much like those of other respiratory and systemic disease. Crenosoma vulpis, for example, can resemble allergic respiratory disease. No sign identifies a parasite on its own, but any of the following warrants a veterinary visit:
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- Persistent cough.
- Breathing difficulty.
- Bleeding abnormalities, such as unusual bruising or bleeding.
- Neurologic signs of any kind.
- Chronic nasal discharge or reverse sneezing, which point toward nasal parasites rather than lung infection.
Breathing difficulty, bleeding problems, and neurologic signs carry the most urgency. Cardiovascular involvement is also reported with A. vasorum, so a dog with breathing signs may need a heart assessment as well as a lung assessment.
The history your vet will want
Because the likely parasite drives the test, a careful exposure history is one of the most useful things an owner can provide. Be ready to describe:
- Location and travel. Parasite distribution and product authorization vary by region and country.
- Snail and slug contact. Including whether the dog eats, licks, or plays with them in damp garden areas.
- Wild and other animal contact. Foxes or other wild canids, frogs, mice, and rats.
- Previous medication. Any dewormer or preventive given, which product, and when.
- Signs and timing. When each sign started, how often it occurs, and whether it comes and goes.
How treatment is chosen
Treatment depends on the suspected or confirmed parasite, the region, the dog’s clinical condition, and the products authorized locally. The drug evidence in guidance is parasite-specific. A medicine studied against one lungworm does not establish a general lungworm treatment, and a drug named in guidance has not necessarily been licensed for that parasite in your country. Ask your vet whether a product is labeled for the parasite being treated or is being used on the basis of study results or clinical guidance. Owner-selected dewormers can be mismatched to the parasite and can delay the correct diagnosis.
Diagnosis and treatment by parasite
Angiostrongylus vasorum (French heartworm)
Adult A. vasorum live in the pulmonary arteries and the right side of the heart. Dogs become infected by eating gastropods carrying infective larvae and, in some circumstances, paratenic hosts such as frogs. A paratenic host carries the larvae without the parasite developing further in it. Infection can inflame the lungs and may produce respiratory, cardiovascular, bleeding, or neurologic problems. CAPC’s guidance on the species is direct about the stakes:
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“Early diagnosis is essential, if left untreated, infections could be fatal.”
Companion Animal Parasite Council, Angiostrongylus vasorum guidance
Diagnostic tests. CAPC identifies two methods as the most effective: Baermann examination of feces and a serum antigen test. Other tests add information:
- Baermann examination of fresh feces. Looks for the larvae the parasite sheds. ESCCAP’s 2025 guideline describes fresh fecal sampling on consecutive days. Shedding varies, so more than one sample may be needed.
- Serum antigen test. A blood test. ESCCAP notes that commercially available antigen testing exists.
- Fecal flotation. Can detect larvae but is less reliable. A single routine flotation may miss them, so a negative flotation does not rule out A. vasorum.
- Chest radiographs. Can show pulmonary changes and may show enlargement of the right heart or pulmonary arteries.
- Bronchoalveolar lavage. ESCCAP lists lavage microscopy as a diagnostic approach. CAPC notes that qPCR on lavage may help in some cases.
Treatment. CAPC reports that A. vasorum has been treated with levamisole, fenbendazole, ivermectin, milbemycin oxime, and moxidectin. These are reported uses rather than an owner dosing guide. Product choice, dose, and duration belong with the veterinarian, and the monitoring needs are described below.
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Crenosoma vulpis (fox bronchial worm)
C. vulpis can cause a persistent cough and may look like allergic respiratory disease, so it is worth testing before assuming allergy. Dogs acquire it by ingesting an infected mollusk, and mice have been described as paratenic hosts. The most effective fecal method in CAPC guidance is Baermann recovery of first-stage larvae.
Treatment evidence. CAPC describes fenbendazole and milbemycin oxime/praziquantel as studied options, along with topical imidacloprid/moxidectin in experimentally infected dogs. In one experimental study, a single oral dose of milbemycin oxime/praziquantel achieved 98.7% efficacy. That is an experimental result for one dose, not a general cure rate for dogs in everyday practice.
Eucoleus aerophilus
This parasite lives in the respiratory tract. It is diagnosed by identifying its eggs in sputum or feces. CAPC describes ivermectin or benzimidazole-class drugs as used for it. Those are reported options, not interchangeable instructions.
Eucoleus boehmi
This parasite lives in the nasal cavity and sinuses. Its eggs can be identified in nasal discharge or feces, and chronic nasal discharge or reverse sneezing may occur. Because it is a nasal and sinus parasite, it is not a lung infection, even though it appears in broad lists of respiratory worms. CAPC’s summary does not give a treatment approach for it, so the choice rests with your vet.
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Filaroides species
CAPC notes that Filaroides species have distinct larval features that affect testing. The laboratory should be told which parasite is suspected. CAPC also describes several treatment approaches for Filaroides infections. These are reported approaches, not instructions to follow.
Angiostrongylus cantonensis (rat lungworm)
This is the rat lungworm. Dogs are incidental hosts, meaning they can be infected without being the parasite’s usual host. Only the rat sheds larvae in feces, so fecal examination is not useful for diagnosing it in dogs. CAPC reports no effective treatment and identifies supportive care as often the only or best option. This is a different clinical situation from canine A. vasorum, and the tests and drugs for one should not be assumed to apply to the other.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.After treatment: monitoring
The follow-up plan depends on the parasite and the drug. Your vet may:
- Repeat fecal or other testing to check whether the infection has cleared.
- Reassess respiratory and cardiovascular findings.
- Monitor coagulation or other abnormalities where indicated.
- Follow repeated-dose schedules or recommend follow-up fecal examination. ESCCAP notes that some products require repeated administration and that follow-up fecal examination may be recommended for some antiparasitic treatments.
With A. vasorum, severe breathing difficulty or ascites (fluid accumulating in the abdomen) may develop after treatment. CAPC notes that bronchodilators, expectorants, diuretics, or other supportive treatment may be needed. Treatment of this parasite should therefore happen where a veterinarian can watch for these reactions, and any sudden worsening of breathing or abdominal swelling warrants an urgent call to the clinic.
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Prevention
Prevention centers on exposure. CAPC’s recommendations differ by parasite:
- A. vasorum: limit exposure to gastropods and to wild canids.
- C. vulpis: prevent access to gastropods.
- General: keep dogs from eating slugs and snails, and reduce exposure to other relevant intermediate or paratenic hosts where possible.
Do not assume that a routine heartworm preventive covers lungworm. CAPC states that routine preventives are probably not protective against these parasites in general. ESCCAP describes prevention as dependent on region and exposure, so ask your vet which approved products are appropriate where you live.
Questions to ask your veterinarian
- Which lungworm are we testing for, and how would each possible result change the plan?
- How many fecal samples do we need, and do we also need an antigen test?
- Are imaging or lavage needed to confirm lung or heart involvement?
- Is the proposed drug authorized in this country for the parasite we suspect?
- What follow-up tests and dates should we plan, and what reactions should prompt an immediate call?
What the current evidence does and does not establish
- Guidance dates vary. CAPC’s species pages carry dates of 2018, 2021, and 2025. CAPC guidance is US-oriented. ESCCAP Guideline 01, seventh edition (June 2025), reflects European guidance. Guidance is revised over time, so confirm the current position with your veterinarian.
- Geography changes the answer. Parasite distribution, diagnostic access, and product authorization differ between countries and regions. A standard approach in one place may not be authorized in another.
- Prevalence is not established. No reliable, broadly representative figure for how common canine lungworm infections are has been established, so this article cannot say how common they are where you live.
- Study results are not individual predictions. Treatment figures describe specific parasites in specific studies. They do not predict how an individual dog will respond.
The Bottom Line
Lungworm is a question of which parasite is involved, not just whether a dog has a lungworm. Testing and treatment follow from the suspected parasite. A clear exposure history and a precise description of the signs give your veterinarian the best starting point, and treatment, especially for A. vasorum, should be planned and monitored by a veterinarian.
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