Metastrongylus spp. (Lungworms)
LEVELS: Highly unlikely: No controls necessary; Highly unlikely: No evidence of non-foodborne zoonotic transmission; Highly effective: Routine on-farm biosecurity measures are effective in preventing farm-to-farm transmission; Moderate: Clinical signs not unique but existing tests available at local/regional laboratory(s); Moderate: Manageable losses related to endemic (population) or chronic (individual) occurrence; Negligible: Little or no market disruption when disease occurs on one or more farms; Minimal risk: Agent inherently unlikely to develop clinically important resistance to antibacterial or antiviral treatments; Minimal risk: Antibacterial or antiviral treatments rarely occur, or are typically limited to short-course individual animal therapy; Widely available: Multiple effective treatments widely available in the US; No availability: Effective vaccines not currently available in the US (or have not been developed); Highly likely: Can be eradicated using existing tools and knowledge
Criteria Levels
- Foodborne Zoonotic Transmission: No evidence of transmission
- Non-Foodborne Zoonotic Transmission: No evidence of transmission
- Beyond-Farm Spread Potential: Farm biosecurity effective
- Detection Difficulty: Moderate: confirmation once suspected
- Financial Impact - Mortality and Morbidity Costs: Manageable chronic losses
- Financial Impact - Prevention and Control Costs: Little market disruption
- Antimicrobial Resistance - Pathogen Risk: Low resistance risk
- Antimicrobial Resistance - Treatment Impact: Minimal: Rare or short-course individual treatments
- Treatment Availability: Multiple effective treatments
- Vaccine Availability: No effective vaccine or bacterin available
- Eradication Feasibility: Can be eradicated using existing tools and knowledge
Overview
Metastrongylus species are lungworms with worldwide distribution, with M. apri being predominant though mixed infections are common. Adults are slender (40-50 mm), occur in bronchi and bronchioles (usually diaphragmatic lobes), and masses of entwined worms covered with mucus may occlude peripheral airways. The indirect life cycle requires earthworm intermediate hosts (Eisenia, Allolobophora spp.), making the parasite primarily a concern for outdoor/pasture-raised pigs where earthworm exposure occurs.
Detailed Justification
1. Foodborne Zoonotic Transmission
Level: No evidence of transmission
Metastrongylus species are host-specific to swine. There is no documented transmission to humans through pork consumption or any other route.
2. Non-Foodborne Zoonotic Transmission
Level: No evidence of transmission
Swine lungworms do not infect humans. No occupational or direct contact transmission occurs.
3. Beyond-Farm Spread Potential
Level: Farm biosecurity effective
The indirect life cycle is the key control point: - "Certain earthworms, notably Eisenia and Allolobophora spp., ingest the eggs. Larvae hatch and invade the earthworm's tissues" - "When swine eat the earthworm, the lungworm larvae migrate to the lungs"
Standard biosecurity is highly effective because pigs must ingest infected earthworms. Confinement on concrete/slats eliminates exposure to intermediate hosts.
4. Detection Difficulty
Level: Moderate: confirmation once suspected
Diagnosis has technical challenges: - "Diagnosis of metastrongylosis is accomplished by finding the characteristic eggs on flotation, but the eggs do not float well" - Alternative: "Postmortem diagnosis is accomplished by trimming 1 cm strips from the edge of the diaphragmatic lung lobe and squeezing to express adults from the bronchi" - Eggs measure 50-60 by 35-40 μm, bear thick rough coat, contain larva
The poor flotation of eggs necessitates either centrifugation techniques or postmortem examination.
5. Financial Impact - Mortality and Morbidity Costs
Level: Manageable chronic losses
Clinical impact is variable: - "Clinical signs are not pronounced, but heavy infections and infections complicated with bacterial infections cause coughing and 'thumping'" - "Lungs with metastrongylosis have wedge-shaped areas of emphysema or atelectasis" - "Concurrent bacterial pneumonia is not uncommon"
The parasite causes chronic respiratory compromise that may predispose to secondary infections, representing manageable ongoing losses.
6. Financial Impact - Prevention and Control Costs
Level: Little market disruption
Lungworm infection is not a regulated disease. There are no trade restrictions or market access issues. Lung condemnations at slaughter represent the primary economic concern beyond production losses.
7. Antimicrobial Resistance - Pathogen Risk
Level: Low resistance risk
Metastrongylus is treated with anthelmintics, not antimicrobials. Traditional AMR concerns do not apply.
8. Antimicrobial Resistance - Treatment Impact
Level: Minimal: Rare or short-course individual treatments
Treatment is with anthelmintics. There is no antimicrobial selection pressure.
9. Treatment Availability
Level: Multiple effective treatments
Multiple effective anthelmintics are available: - Macrocyclic lactones: "control... Metastrongylus (adults)" - Fenbendazole: "labeled for the treatment of... Metastrongylus" - Levamisole: "effective for the treatment of... Metastrongylus"
10. Vaccine Availability
Level: No effective vaccine or bacterin available
No vaccine is mentioned. Control relies on preventing earthworm exposure and anthelmintic treatment.
11. Eradication Feasibility
Level: Can be eradicated using existing tools and knowledge
Eradication is straightforward in modern systems: - "Maintaining pigs on slats or concrete will prevent infection with... metastrongyloids" - The requirement for earthworm intermediate hosts makes elimination simple - remove access to soil/earthworms - Effective anthelmintics available for treating existing infections
The indirect life cycle is actually an advantage for control - breaking the earthworm exposure eliminates the parasite.
Summary
Metastrongylus species are lungworms found in bronchi and bronchioles of swine worldwide. Adults form mucus-covered masses that can occlude airways, causing coughing, respiratory distress ("thumping"), and predisposing to secondary bacterial pneumonia. The indirect life cycle requiring earthworm intermediate hosts means the parasite is primarily a concern for outdoor/pasture-raised pigs. Diagnosis can be challenging because eggs float poorly; postmortem bronchial examination is more reliable. Multiple effective anthelmintics exist. Eradication is straightforward in confinement systems - maintaining pigs on concrete or slats eliminates earthworm exposure and breaks the life cycle. The parasite has no zoonotic potential.