Metastrongylosis in Pigs: Lungworm Infection, Cough, and Outdoor Pig Risk
- Metastrongylosis is a lungworm infection caused by Metastrongylus species that live in the airways of pigs.
- Outdoor and pasture-raised pigs are at higher risk because pigs become infected by eating earthworms that carry the parasite.
- Common signs include coughing, reduced growth, exercise intolerance, and heavier breathing. Mild infections may cause few obvious signs.
- Your vet may diagnose it with fecal testing, herd history, and sometimes necropsy or airway-focused evaluation because lungworm shedding can be intermittent.
- Treatment options often include deworming drugs used in swine, such as ivermectin, doramectin, or fenbendazole, plus management changes to reduce reinfection.
What Is Metastrongylosis in Pigs?
Metastrongylosis is a parasitic lung disease of pigs caused by Metastrongylus species, often called pig lungworms. Adult worms live in the bronchi and bronchioles, where they irritate the airways and can contribute to coughing, airway inflammation, and reduced performance. Merck Veterinary Manual lists Metastrongylus spp. as the lungworms of pigs and notes that affected pigs are treated with swine anthelmintics such as ivermectin, doramectin, or fenbendazole.
This parasite matters most in pigs raised outdoors, on pasture, or in smallholder settings. Indoor pigs on concrete or slatted flooring have much lower exposure risk. In many pigs, infection is mild, but heavier burdens can lead to bronchitis, poor weight gain, and pneumonia-like illness, especially in younger pigs or in pigs dealing with other respiratory problems at the same time.
For pet parents, the big takeaway is that a chronic cough in an outdoor pig is not always "dust" or a routine respiratory infection. Lungworms are one possible cause, and your vet can help sort out whether parasites, bacteria, viruses, or a combination of problems are involved.
Symptoms of Metastrongylosis in Pigs
- Chronic or intermittent coughing
- Faster or more effortful breathing
- Reduced growth or poor weight gain
- Exercise intolerance or tiring easily
- Rough hair coat or thriftiness problems
- Wheezing or noisy breathing
- Secondary pneumonia signs such as lethargy, fever, or nasal discharge
- Open-mouth breathing or marked respiratory distress
Many pigs with light infections show mild signs or none at all. When signs do appear, coughing is the most common clue, especially in young outdoor pigs. Heavier infections can reduce growth and make pigs look less thrifty over time.
See your vet immediately if your pig has labored breathing, blue or gray gums, collapse, severe lethargy, or signs of pneumonia. Lungworms can also occur alongside bacterial or viral respiratory disease, so worsening cough or breathing effort deserves prompt veterinary attention.
What Causes Metastrongylosis in Pigs?
Metastrongylosis is caused by infection with Metastrongylus lungworms. The life cycle is indirect, which means pigs do not usually get infected directly from another pig. Instead, the parasite uses earthworms as an intermediate host. Pigs become infected when they root and eat infected earthworms while living outdoors or on contaminated ground.
This is why outdoor pigs, pasture pigs, backyard pigs, and feral pigs face the highest risk. Reports from swine field surveillance have repeatedly linked lungworm cases to outdoor units, and long-term carryover on land is possible because earthworms can maintain the parasite for years.
Risk tends to be higher in younger pigs, pigs rotated onto previously contaminated ground, and herds with inconsistent parasite control. Reinfection is common if treatment is used without changing management, because the environment can continue to expose pigs after the first round of deworming.
How Is Metastrongylosis in Pigs Diagnosed?
Your vet will usually start with history and risk assessment. A cough in an outdoor pig, especially one with access to soil and earthworms, raises suspicion for lungworms. Your vet will also consider other common causes of pig cough, including bacterial pneumonia, viral respiratory disease, and mycoplasma-related disease.
Testing may include fecal parasite evaluation, but lungworm detection can be tricky. Merck notes that larval shedding in feces can be sporadic in lungworm infections, which means a single negative sample does not always rule the problem out. In herd situations, your vet may recommend repeat testing, fresh sample collection, or evaluation of multiple pigs.
In some cases, diagnosis is supported by response to treatment, herd pattern, or findings at necropsy. Postmortem examination can directly identify worms in the airways and helps confirm whether lungworms are the main problem or part of a mixed respiratory disease picture.
Treatment Options for Metastrongylosis in Pigs
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Farm or ambulatory exam focused on cough and breathing
- Targeted deworming plan using labeled swine products chosen by your vet
- Basic herd-history review for outdoor exposure and pasture risk
- Monitoring appetite, breathing effort, and weight gain at home
- Simple management changes such as moving pigs off high-risk ground when possible
Recommended Standard Treatment
- Veterinary exam plus fecal testing or repeat fecal testing
- Evidence-based deworming with swine options listed by Merck, such as ivermectin 0.3 mg/kg SC, doramectin 0.3 mg/kg SC, or fenbendazole 9 mg/kg in feed for 3-12 days, as directed by your vet
- Assessment for concurrent respiratory infection
- Supportive care recommendations for hydration, housing, and stress reduction
- Follow-up plan to reduce reinfection in outdoor pigs
Advanced / Critical Care
- Urgent or emergency evaluation for pigs with respiratory distress
- Expanded diagnostics such as bloodwork, imaging where feasible, and herd-level workup
- Treatment for severe secondary pneumonia or dehydration if present
- Hospitalization, oxygen support, or intensive monitoring when breathing effort is high
- Necropsy and herd investigation if deaths occur or the diagnosis remains unclear
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Metastrongylosis in Pigs
Bring these questions to your vet appointment to get the most out of your visit.
- Does my pig's cough fit lungworm, pneumonia, or both?
- What tests are most useful in this case, and would repeat fecal testing help if the first sample is negative?
- Which dewormer is appropriate for my pig's age, weight, and intended use?
- Do we need to treat one pig, all exposed pigs, or the whole group?
- How likely is reinfection on this pasture or yard?
- What housing or rotation changes would lower exposure to infected earthworms?
- Are there signs that suggest a secondary bacterial or viral respiratory infection too?
- What meat withdrawal or food-safety rules apply if this pig is part of a production setting?
How to Prevent Metastrongylosis in Pigs
Prevention focuses on reducing exposure to infected earthworms and lowering environmental contamination. Pigs kept fully indoors on concrete or slatted floors have much lower risk than pigs raised on pasture or dirt lots. If your pig lives outdoors, talk with your vet about a parasite-control plan that fits your pig's age, housing, and local risk.
Good prevention may include strategic deworming, rotating pigs away from heavily used ground, avoiding repeated use of the same contaminated outdoor areas, and keeping new pigs on a separate health plan before mixing. Management matters because treatment alone may not stop the cycle if pigs return to the same exposure source.
If one pig in a group is coughing, it is worth reviewing the whole setup rather than focusing only on that individual. Your vet can help decide whether the best next step is conservative monitoring, group treatment, or a broader herd-health approach.