Flies Can Transmit Porcine Epidemic Diarrhea Virus 🐖

by Dr Duncan Houston, DVM — 2025

1. Introduction: A Hidden Vector

Porcine Epidemic Diarrhea Virus (PEDV) is a serious coronavirus affecting pigs, especially piglets, leading to severe diarrhea and high mortality. The fecal–oral route is the primary transmission pathway—but recent research highlights an unexpected vector: flies 🦟. This article delves into the role of flies in spreading PEDV, the implications for swine biosecurity, and practical control strategies.

2. What is PEDV?

PEDV targets the small intestine, wiping out villi and causing dehydration, vomiting, and nearly 100% mortality in neonatal piglets. Older pigs recover in 7–10 days but still suffer production setbacks. Discovered in Europe in the 1970s, PEDV resurfaced in North America in 2013 and now poses a major economic threat. The virus can also spread via aerosols, respiratory secretions, fomites, and contaminated feed. :contentReference[oaicite:5]{index=5}

3. Traditional Transmission Modes

1. Fecal–oral route: Direct ingestion of contaminated feces. :contentReference[oaicite:6]{index=6}
2. Aerosols: Virus-laden droplets can travel through the air. :contentReference[oaicite:7]{index=7}
3. Fomites: Equipment, trucks, clothes can spread PEDV across farms.

4. Flies: The Unexpected Carrier

Experts suspected flies could spread PEDV, given their contact with pig manure. Dr Grant Allison’s research confirmed this: flies captured from PEDV-affected barns yielded positive PCR results, and importantly, live virus that transmitted disease in a bioassay. :contentReference[oaicite:8]{index=8}

4.1 Larval habitats & fly behavior

Flies breed in moist manure—ideal conditions for virus persistence. They move freely throughout barns, contacting feed, water, and pig surfaces.

4.2 PCR vs live-virus bioassay

While PCR detects viral genetic material, bioassay confirms that flies can carry infectious virus capable of infecting naive pigs. :contentReference[oaicite:9]{index=9}

4.3 Seasonal persistence

Fly activity was documented even during winter months, indicating risk is not limited to warm seasons. :contentReference[oaicite:10]{index=10}

5. Implications for Disease Control

• Expanded biosecurity: Traditional methods miss fly vectors—this must change.
• Year‑round vigilance: Monitoring and control are needed through all seasons.
• Manure management: Flies thrive in untreated waste—correct removal and drying are essential.
• Integration: Combine fly management with other biosecurity protocols.

6. Practical Control Strategies

6.1 Adult fly control

Use foggers, misters, or baits—approved for agricultural use. These target adult flies and reduce viral spread.

6.2 Larval control

Feed-through larvicides target flies in manure pits, interrupting life cycle. Popular options include insect growth regulators.

6.3 Manure & facility hygiene

• Prompt removal and storage in sealed containers.
• Dry manure thoroughly to inhibit larval development.
• Clean tools and equipment regularly to disrupt breeding habitats.

6.4 Monitoring & integration

Use fly traps to quantify populations and time control. Include fly management in biosecurity drills, training personnel accordingly.

7. Case Study Example

A farm in Iowa introduced a combined fogging and feed-through larvicide regimen after a PEDV outbreak. It saw a ≥70% drop in fly numbers and no recurrence over six months. Precise metrics are needed, but anecdotal success supports integrated programs.

8. Challenges & Limitations

• Resistance: Monitor for decreased efficacy due to resistance.
• Cost: Investment in equipment and products is necessary—but payoff in reduced disease losses.
• Environmental balance: Avoid harmful chemicals; use agricultural-approved products only.
• Knowledge gaps: More research needed on dose, timing, and vector dynamics.

9. Integration with Broader Biosecurity

Fly control complements:

• Quarantine new animals and vehicles.
• Disinfection protocols using effective virucidal agents.
• Air filtration near entrances to prevent aerosol entry.
• Staff hygiene and PPE to avoid mechanical transmission.

10. Summary & Future Directions

The discovery that flies can spread PEDV fundamentally changes our biosecurity strategies. Dr Allison’s findings provide compelling evidence for including fly control in all PEDV prevention programs. Farms should:

• Accept fly control as essential—not optional.
• Implement both adult and larval control strategies.
• Maintain year‑round vigilance.
• Combine fly management with other biosecurity measures.

Future research priorities include tracking fly populations over seasons, field trials of control strategies, and developing predictive models. Reducing fly populations now helps protect pig health and industry sustainability.

11. Key Takeaways 📌

• Flies harbor live PEDV and transmit it to pigs in research settings. :contentReference[oaicite:11]{index=11}
• Traditional control measures miss this vector—expanded biosecurity needed.
• Control must be year‑round; winter doesn’t eliminate the risk. :contentReference[oaicite:12]{index=12}
• Use adult fogging, larval feed-through agents, and strict manure hygiene.
• Monitor fly numbers, add to biosecurity protocols, and train staff.

12. Resources & Further Reading

• Research papers on PEDV transmission in pigs and flies. :contentReference[oaicite:13]{index=13}
• PEDV summaries, diagnosis & transmission. :contentReference[oaicite:14]{index=14}

📝 Author: Dr Duncan Houston, DVM
🗓️ Date: 2025
🐷 Category: Swine Health & Biosecurity