PEDV in Pigs: How Flies Spread Infection and What to Do to Stop It

By Dr Duncan Houston

Porcine epidemic diarrhea virus (PEDV) is one of the most devastating diseases in pig production, particularly for neonatal piglets. Most producers understand the classic transmission routes like contaminated manure, equipment, and personnel.

What is often underestimated is this:

Flies can carry and spread live, infectious PEDV.

This changes how biosecurity needs to be approached. If fly control is not part of your system, then your system is incomplete.

This guide explains how PEDV actually spreads, the role flies play, what this means for your farm, and what practical steps reduce risk.

Quick Answer

PEDV spreads primarily through contaminated feces, but flies can also carry infectious virus between pigs and facilities. This means fly control is a critical part of biosecurity. Without managing flies, PEDV can persist and spread even when traditional hygiene protocols are in place. If PEDV is present or suspected, immediate action should include both infection control and aggressive fly management.

Why PEDV Is Such a Serious Disease

PEDV targets the intestinal lining.

In piglets, this leads to:

• Severe diarrhea

• Rapid dehydration

• Collapse

• Extremely high mortality

Older pigs often survive, but:

• Growth is reduced

• Feed efficiency drops

• Production losses increase

Clinical Insight

The biggest losses are not just mortality. It is the combination of death, growth setback, and ongoing production impact across the herd.

How PEDV Traditionally Spreads

Most producers are familiar with:

Fecal-Oral Transmission

• Direct ingestion of contaminated manure

• The most important and consistent route

Fomites

• Equipment

• Trucks

• Boots

• Clothing

Aerosol Spread

• Virus-containing particles

• Possible under certain conditions

Decision Checkpoint

If your biosecurity plan only focuses on these routes, you are missing a key vector.

Flies: The Missing Link in Many Biosecurity Programs

Flies interact with:

• Manure

• Feed

• Water

• Animals

They move freely between contaminated and clean areas.

What Research Shows

Studies have demonstrated:

• Flies collected from infected barns test positive for PEDV

• Live virus can be isolated from flies

• Flies can transmit infection to naïve pigs

Clinical Insight

This is not just contamination. This is transmission of infectious virus.

Why Flies Are Such Effective Vectors

Behaviour

Flies:

• Breed in manure

• Move rapidly between areas

• Land on feed and water

• Contact multiple animals

Environmental Advantage

• Thrive in moist, organic environments

• Persist in both warm and cooler conditions

• Can remain active even outside peak summer

Decision Checkpoint

If manure management is poor or fly populations are high, PEDV risk increases significantly.

When Is the Risk Highest?

High-Risk Periods

• Warm weather

• High humidity

• Increased manure accumulation

• High stocking density

Important Insight

Fly risk is not strictly seasonal. Winter activity still occurs, particularly in enclosed systems.

What This Means for Biosecurity

Traditional biosecurity alone is not enough.

You must integrate:

• Hygiene

• Movement control

• Fly control

Clinical Insight

Most outbreaks occur when multiple small gaps align. Flies often represent one of those overlooked gaps.

Severity Framework: How Big Is the Risk?

Low Risk

• Strong hygiene

• Low fly population

• Controlled manure

Moderate Risk

• Seasonal fly increase

• Occasional hygiene gaps

High Risk

• High fly numbers

• Poor manure management

• Active PEDV in the region

Critical

• Active PEDV outbreak

• High fly activity

• Poor containment

Immediate intervention required.

Practical Fly Control That Actually Works

Adult Fly Control

• Fogging systems

• Misting systems

• Fly baits and traps

Larval Control

• Feed-through larvicides

• Insect growth regulators

• Target manure breeding sites

Manure Management

• Remove manure frequently

• Keep areas dry

• Store waste properly

• Prevent accumulation

Environmental Control

• Reduce standing water

• Improve drainage

• Maintain clean surfaces

Decision Checkpoint

If you can see flies consistently in the facility, control measures are already insufficient.

Monitoring Fly Pressure

• Use traps to track population

• Monitor trends over time

• Adjust control strategies based on numbers

Clinical Insight

Fly control is not a one-time action. It is an ongoing system that needs monitoring.

What to Do During a PEDV Outbreak

If PEDV is present:

1. Isolate affected animals

2. Stop unnecessary movement

3. Intensify cleaning and disinfection

4. Implement aggressive fly control immediately

5. Review manure management

6. Train staff on containment protocols

Time-Based Guidance

• Immediate: isolate and control

• First days: reduce spread

• Ongoing: monitor and adjust

Common Mistakes Producers Make

• Ignoring flies as a transmission route

• Treating fly control as optional

• Poor manure management

• Inconsistent hygiene protocols

• Not monitoring fly populations

• Focusing only on visible contamination

Integrating Fly Control Into Biosecurity

Fly control should sit alongside:

• Quarantine protocols

• Equipment disinfection

• Staff hygiene

• Movement control

• Airflow management

Clinical Insight

The strongest systems are layered systems. Removing one layer increases overall risk.

Economic Impact

Failure to control PEDV leads to:

• Piglet mortality

• Reduced growth

• Increased treatment cost

• Production delays

• Long-term herd impact

What Should You Do Right Now?

If you are concerned about PEDV risk:

1. Assess fly population

2. Review manure management

3. Check hygiene protocols

4. Implement adult and larval control

5. Monitor pig health closely

6. Adjust protocols immediately if risk increases

FAQs

Can flies really spread PEDV?

Yes. Research shows they can carry and transmit live virus.

Is fly control enough on its own?

No. It must be combined with full biosecurity.

Is PEDV seasonal?

More common in warm months, but not limited to them.

How quickly can PEDV spread?

Very quickly, especially in young piglets.

What is the most important prevention step?

Layered biosecurity, including fly control.

Final Thoughts

PEDV control is not about one solution.

It is about closing every gap.

The key factors are:

• hygiene

• movement control

• manure management

• fly control

• early response

Flies are often the missing piece.

If you ignore them, you leave the door open.

If you want help reviewing biosecurity gaps, improving fly control programs, or responding to PEDV risk early, ASK A VET™ can help you act before losses occur.