🩺 Atypical Porcine Pestivirus (APPV) in Piglets

By Dr Duncan Houston, DVM – Updated 2025

Atypical Porcine Pestivirus (APPV) is an emerging viral infection affecting neonatal piglets, causing congenital tremors and splay-leg syndrome. These conditions impair piglets' ability to nurse and move, leading to increased preweaning mortality. This detailed vet guide—geared for pig producers, veterinarians, and barn managers—dives into APPV's biology, clinical impact, diagnostics, prevention, and control strategies. Let’s unpack it! 🧬

1. 🔍 What is APPV?

APPV is a novel RNA virus within the Pestivirus genus that primarily targets newborn piglets. It disrupts neuromuscular control, resulting in tremors and splay-leg postures. Unlike other pestiviruses (like classical swine fever), APPV is not typically fatal—but its secondary impacts can be devastating. First identified in the early 2010s, it has since been detected globally. (veterinarypartner.vin.com)

2. 🐖 Clinical Signs in Affected Piglets

The hallmark symptoms appear at birth or within hours:

• Congenital tremors: Shaking of head, limbs, or entire body—ranging from mild to severe.
• Splay-leg: Limbs flail outward, preventing normal standing or crawling posture.
• Poor suckling: Piglets struggle to latch and feed, leading to weight loss or death.
• Death: Often indirect—via starvation, crushing, hypothermia, or secondary infection.

Severity correlates with tremor intensity and mobility issues.

3. 🌱 How Does the Virus Spread?

Primary routes include:

• Vertical transmission: From infected sow to piglets prior to or during birth.
• Horizontal spread: Via contaminated oral fluids among sows, piglets, or replacement stock.
• Semen contamination: Natural mating or artificial insemination with APPV-positive semen.

New, naïve herds are especially vulnerable during introduction of untested gilts or semen. (veterinarypartner.vin.com)

4. 📉 Impact on Production

• Elevated mortality: Mortality rates vary but often spike due to compromised piglet viability.
• Extra labor: Neonatal piglets require intensive care—tube feeding, warming, protection.
• Wasted space: Sick piglets occupy farrowing slots longer or require removal.
• Herd reputation: Buyers may avoid producers with APPV recurrence.

5. 🧪 Diagnostic Methods

Accurate detection relies on these tools:

• PCR testing: Molecular detection of APPV RNA in serum or oral-fluid swabs. Highly reliable early indicator. (veterinarypartner.vin.com)
• Oral fluid sampling: Non-invasive method to detect viral presence at pen or group level.
• Semen testing: Critical for boar studs; studies show up to 99% positivity in infected semen. (veterinarypartner.vin.com)
• Clinical assessment: Observational confirmation of tremor and mobility dysfunction in newborn litters.

6. 🧩 Epidemiological Case Study

In one naïve gilt herd, early 2020 saw sudden onset of congenital tremors and splay-leg. Laboratory samples identified APPV DNA. Oral fluids taken from growing pigs revealed herd-wide virus prevalence:

• Nursery exit: 37% positive.
• End of study: 77% positive.
• Finishers: 100% oral-fluid positivity.
• Semen: ~98.9% APPV-positive.

This demonstrated rapid within-herd spread and demonstrated semen’s role in viral dissemination. (veterinarypartner.vin.com)

7. 🛡️ Prevention & Biosecurity Measures

a) Quarantine Procedures

• Incoming gilts: Isolate for 30–45 days. Perform serial oral-fluid or serum PCR tests before introduction to herd.
• Boar studs and semen: Routine PCR screening of semen batches.

b) Herd Monitoring

• Email oral-fluid testing at regular intervals for sow and gilt units.
• Track FARROWINGS for congenital tremors or splay-leg—flag litters early.

c) Segregation & Flow

• Maintain age-based flow—nursery, grow-finish, and sow units separated.
• Cease gilt recycling during suspected APPV outbreaks to limit new virus input.

d) Genetic Management

• Pre-breeding PCR screening for replacement breeding stock and AI lots.
• Only purchase APPV-tested genetics from accredited suppliers.

8. 🧬 Can APPV Be Eradicated?

Eradication is complex due to virus persistence in semen and widespread subclinical infections. Key strategies include:

• Effective quarantine and testing of boars and gilts.
• Semen PCR testing prior to use in AI.
• Strict biosecurity: equipment sanitization, barrier systems, and personnel protocols.
• Elimination of persistently infected animals.

9. ⚠️ Long-Term Surveillance

• Regular sampling of oral fluids from growing pigs and breeding flock to confirm virus suppression.
• Monthly monitoring of farrowing outcomes—especially in new gilt batches.
• Seasonal monitoring recommended during gilt acclimation phases.

10. 📈 Economics & ROI

Investing in APPV controls pays off:

• Reduced mortality: Less need for veterinary intervention, decreased losses.
• Labor savings: Fewer piglets needing special care.
• Quality assurance: Higher piglet uniformity and performance.
• Marketability: Ability to supply APPV-tested stock adds premium value.

11. 📚 Practical Action Plan

Task	Goal	Timing
Quarantine incoming gilts	Detect APPV before herd introduction	30–45 days + PCR
Test boar semen	Prevent viral entry via AI	Each batch, prior to use
Oral-fluid testing	Monitor herd infection	Monthly
Farrowing surveillance	Early clinical detection	Continuous, weekly report
Genetic sourcing	APPV-free breeding stock	Before purchase
Quarantine record-keeping	Ensure compliance	Ongoing

12. 🧠 Lessons Learned

• Silent carriers: Asymptomatic animals still shed virus—testing is essential.
• Semen is a vector: High APPV prevalence in semen highlights potential for AI transmission.
• Quarantine works: Even sources appearing healthy may harbor virus.
• Surveillance matters: Regular testing catches outbreaks early.

13. 💬 Mythbusters

• “Only symptomatic pigs spread APPV.” False—PCR-positive asymptomatic pigs shed virus.
• “Commercial semen is safe.” Not always—up to ~99% of ejaculates test positive in infected herds.
• “Once infected, sows won’t pass it again.” Re-infection or recrudescence may occur—monitor each batch.

14. ✅ When to Call the Vet

• First observation of congenital tremors or splay-leg.
• Unexpected increase in piglet preweaning mortality.
• Positive test results in quarantine or production herds.

Your veterinarian will help interpret diagnostics and develop targeted herd protocols.