Atypical Porcine Pestivirus in Piglets: Congenital Tremor, Diagnosis and Herd Control

By Dr Duncan Houston

A newborn piglet that shakes violently whenever it tries to stand or reach the udder may have congenital tremor caused by atypical porcine pestivirus.

The tremor itself is not always directly fatal. The real danger is that severely affected piglets cannot stay warm, compete for a teat, ingest enough colostrum or move away from the sow. Starvation, hypothermia and crushing may then produce heavy losses during the first few days of life.

APPV deserves serious investigation, but congenital tremor is a clinical syndrome rather than a diagnosis by appearance alone. Birth-onset tremor, splay leg, weakness and neurological disease have other infectious, genetic, toxic and management-related causes.

Quick Answer

Atypical porcine pestivirus, currently classified as Pestivirus scrofae, is a major cause of congenital tremor type A-II in newborn piglets. Infection of the fetus during gestation can produce action-associated shaking, poor coordination and difficulty nursing.

Piglets that remain warm, upright and able to nurse may improve over days or weeks. Piglets that cannot stand, cannot latch, become cold or weak, or are repeatedly at risk of crushing require immediate hands-on support and veterinary assessment. RT-qPCR testing of individual piglets and appropriate tissues is needed to confirm APPV and rule out other causes. (ICTV)

APPV at a Glance

Question	Practical answer
What is APPV?	An enveloped RNA pestivirus of pigs, officially classified as Pestivirus scrofae
What disease does it cause?	Congenital tremor type A-II following fetal infection
When do signs appear?	At birth or immediately afterwards
What do the tremors look like?	Shaking that becomes more obvious during voluntary movement
Are piglets always affected equally?	No. Severity may vary markedly within the same litter
Does APPV always cause splay leg?	No. Splay leg is multifactorial, although it may occur alongside APPV-associated tremor
How does it spread?	Vertical fetal infection causes clinical disease; horizontal spread is often subclinical
Can apparently normal pigs carry APPV?	Yes
Can semen contain APPV RNA?	Yes, but venereal infectivity remains unconfirmed
Is there a commercial vaccine?	No established commercial vaccine is currently available
Is there an antiviral cure?	No. Treatment is supportive
Main production risk	Failure to nurse, hypothermia, crushing and increased preweaning mortality

APPV-associated disease is best understood as a problem of prenatal infection followed by impaired neonatal survival, rather than a simple neurological curiosity. (Springer Nature Link)

What Is Atypical Porcine Pestivirus?

Atypical porcine pestivirus is a positive-sense, single-stranded RNA virus belonging to the pestivirus group. Its current official species name is Pestivirus scrofae, while the previous taxonomic designation was Pestivirus K. (ICTV)

APPV was first identified in the United States in 2015 through high-throughput sequencing. At the time of discovery, it was detected without a clearly established disease association. Subsequent field studies and controlled fetal-infection experiments connected APPV with congenital tremor type A-II. (OUP Academic)

Researchers reproduced congenital tremor by exposing pregnant animals or fetuses to APPV-containing material. In the original experimental work, affected litters had congenital-tremor prevalence ranging from 57% to 100%, while control litters remained unaffected. This provides far stronger evidence of causation than simply detecting viral RNA in a naturally affected piglet. (PubMed Central (PMC))

Is APPV the Same as Classical Swine Fever Virus?

No.

APPV and classical swine fever virus are both pestiviruses, but they are different viral species with very different regulatory and disease implications. ICTV currently classifies APPV as Pestivirus scrofae and classical swine fever virus as Pestivirus suis. (ICTV)

APPV is primarily associated with congenital tremor and subclinical circulation in pigs. Classical swine fever can cause severe systemic, reproductive, haemorrhagic and neurological disease and is reportable in many countries.

Congenital tremor accompanied by fever, widespread haemorrhage, abortions, multiple age groups becoming ill or unexplained high mortality requires urgent investigation for diseases beyond APPV.

What Does APPV Congenital Tremor Look Like?

APPV-associated congenital tremor is normally present at birth.

The tremor is often described as an intention or action tremor. It becomes more obvious when the piglet attempts to:

Stand
Walk
Find the udder
Maintain posture
Compete with littermates
Respond to handling

The head, trunk and limbs may all be affected. Some piglets show only fine shaking around the head or hindquarters, while others shake so intensely that coordinated movement becomes extremely difficult. (Springer Nature Link)

Tremors may decrease when the piglet is resting or sleeping. This distinction is useful because continuous convulsions, altered consciousness or episodic collapse raise greater concern for hypoglycaemia, meningitis, toxic disease or another neurological problem.

Common Clinical Signs

Affected piglets may show:

Generalised shaking
Head and limb tremors
Difficulty standing
Frequent falling
Poor coordination
Difficulty reaching or maintaining attachment to a teat
Reduced colostrum and milk intake
Splay leg
Reduced growth
Hypothermia
Weakness
Increased crushing risk

Clinical severity may differ considerably between littermates, and visually normal littermates may still be APPV-positive. (Springer Nature Link)

Do the Tremors Go Away?

Many piglets improve gradually during the first few days or weeks of life.

However, improvement is not guaranteed. Tremors have persisted until slaughter age in some pigs and may recur or become more obvious during stress. A pig that has stopped visibly trembling may also remain APPV-viraemic and capable of contributing to transmission. (Springer Nature Link)

This is one of the more inconvenient APPV facts: clinical recovery does not necessarily mean virological clearance.

Does APPV Cause Splay Leg?

APPV can occur in litters with splay leg, and experimental or field investigations have reported a higher incidence of splayed limbs among piglets affected by congenital tremor.

In one high-mortality field investigation, 33% of piglets with congenital tremor had splayed legs, compared with less than 1% of unaffected piglets. That association belonged to one outbreak and does not prove that APPV causes every naturally occurring case of splay leg. (OUP Academic)

A separate study investigating naturally occurring congenital tremor and splay leg found APPV-associated antiviral responses in tremor cases but found no evidence supporting one common infectious cause for splay leg. (Springer Nature Link)

Splay leg is considered multifactorial. Possible contributors include:

Genetic susceptibility
Low birth weight or developmental immaturity
Myofibrillar underdevelopment
Intrauterine nutritional effects
Farrowing induction and timing
Slippery flooring
Litter size
Other congenital or infectious abnormalities

The practical conclusion is:

APPV should be investigated when congenital tremor and splay leg occur together, but splay leg without tremor should not automatically be labelled APPV.

Why Can APPV Increase Piglet Mortality?

The virus does not need to kill the piglet directly to produce major production losses.

Severely affected piglets may be unable to:

Reach the udder quickly
Maintain suction
Compete for productive teats
Consume enough colostrum
Remain beneath the heat source
Move away from the sow
Recover after being displaced by littermates

The resulting deaths may be recorded as starvation, crushing, hypothermia or low viability rather than viral mortality.

In one intensively studied outbreak, preweaning mortality was 46.4% in piglets with congenital tremor compared with 15.3% in unaffected piglets. More than half of the affected-piglet deaths occurred during the first day, and 76% occurred during the first five days. These figures demonstrate the potential impact of a severe outbreak but should not be applied as universal APPV mortality rates. (OUP Academic)

Other outbreaks have reported lower mortality. The outcome depends on:

Tremor severity
Number of affected piglets
Birth weight
Farrowing supervision
Colostrum availability
Environmental temperature
Flooring and crate design
Cross-fostering practices
Sow behaviour
Nursing support

How Worried Should You Be?

Lower Risk

The piglet:

Has a mild tremor
Can stand and walk
Reaches a teat independently
Maintains suction
Remains warm
Has a full abdomen after nursing
Is gaining weight

What it means: APPV is still possible, but the immediate survival risk is lower.

What to do: Record the piglet, monitor nursing and weight closely, and arrange diagnostic sampling if several piglets or litters are affected.

Moderate Concern

The piglet:

Falls intermittently
Takes longer to reach the udder
Loses the teat repeatedly
Has mild or moderate splay leg
Requires occasional assistance
Is smaller or colder than littermates

What it means: The tremor is beginning to interfere with normal neonatal function.

What to do: Provide frequent assistance to nurse, monitor temperature and body weight, reduce competition and have the litter assessed by the herd veterinarian.

High Concern

The piglet:

Cannot stand reliably
Cannot attach to a teat without help
Is becoming weak
Has an empty abdomen
Is persistently cold
Is repeatedly trapped beneath the sow
Has marked splay leg
Belongs to one of several affected litters

What it means: Starvation, hypothermia and crushing are immediate threats.

What to do: Begin intensive neonatal support and obtain same-day veterinary assessment. Collect diagnostic samples before affected piglets die or are moved extensively between litters.

Critical

The piglet has:

Severe hypothermia
Minimal responsiveness
Inability to swallow
Severe dehydration
Respiratory distress
Blue or grey mucous membranes
Repeated true seizures
Major trauma
Complete inability to stand or nurse
Progressive suffering despite support

What it means: This is no longer simply a diagnostic APPV question. The piglet is critically compromised.

What to do: Provide immediate hands-on veterinary care and assess whether continued treatment or humane euthanasia offers the better welfare outcome.

How Does APPV Spread?

APPV transmission must be separated into two clinically different patterns.

Vertical Transmission

Vertical infection occurs when APPV crosses the placenta and infects developing fetuses.

This is the route associated with congenital tremor. The effect appears to depend partly on:

Stage of gestation
Maternal immune status
Viral strain
Fetal susceptibility
Viral dose
Possibly host genetics

Experimental work confirms that prenatal infection can produce congenital tremor in newborn piglets. (PubMed Central (PMC))

Horizontal Transmission

Pigs may acquire APPV after birth through contact with infected pigs or contaminated secretions.

Viral RNA has been detected in:

Blood
Saliva
Oral fluids
Urine
Faeces
Preputial material
Semen
Multiple internal tissues

Horizontal infection is generally subclinical. A pig infected after birth may therefore spread APPV without developing tremors. Clinical congenital disease requires fetal exposure before birth. (Springer Nature Link)

This helps explain why the virus can circulate widely through nursery, grower, finisher and breeding populations without an obvious neurological outbreak in every group.

Can APPV Be Spread Through Semen?

APPV RNA has repeatedly been detected in boar semen, but detecting RNA is not the same as proving that an artificial insemination dose contains infectious virus capable of establishing fetal infection.

A 2018 U.S. investigation detected APPV RNA in 59 of 457 commercial semen samples, approximately 12.9%. (Wiley Online Library)

A 2026 Norwegian study detected APPV RNA in raw semen from 56 of 110 young breeding boars. Shedding generally lasted less than three months, although one boar showed intermittent detection for up to seven months. Viral RNA was also detected in reproductive tissues after some animals had become semen-negative. (Springer Nature Link)

However, that study specifically concluded that further virus-isolation and experimental-infection work is required to establish:

Whether the detected virus is infectious
The minimum infectious dose
Whether processed AI doses transmit infection
How efficiently naïve sows become infected
Whether such infection produces congenital tremor

The authors considered it premature to propose a defined universal screening strategy for boar studs. (Springer Nature Link)

What Did the 98.9% Semen Result Mean?

A production-system investigation found that the APPV sequence from a clinically affected piglet was 98.9% genetically similar to the sequence detected in an incoming semen dose.

That did not mean 98.9% of semen doses were positive.

The high sequence identity supported semen as a possible introduction route, but it did not definitively prove transmission. Closely related virus may have been circulating elsewhere within the production system. (PubMed Central (PMC))

That same investigation recorded increasing APPV detection through the production flow. Nursery pen-level oral-fluid positivity increased from 37.5% to 77.5%, while all sampled finisher oral-fluid ropes were positive at two later sampling points. Those findings demonstrate extensive horizontal circulation, not that every individual pig was infected or infectious at every time point. (Locus)

Can Apparently Healthy Pigs Shed APPV?

Yes.

A 2026 cohort study followed piglets from congenital-tremor outbreak herds. Piglets with tremor and some visually healthy littermates were viraemic at birth. Of the pigs from affected litters remaining in the study, 53% were still viraemic at approximately four months of age. (Springer Nature Link)

Important findings included:

Some pigs stopped trembling while remaining viraemic.
Some tremoring pigs became PCR-negative before their signs disappeared.
Tremor severity did not reliably predict viral load.
Healthy littermates could be APPV-positive.
Pigs from initially unaffected litters became infected after groups were mixed.

This means visual examination alone cannot identify all pigs capable of contributing to APPV spread. (Springer Nature Link)

Does APPV Cause Persistently Infected Pigs?

APPV can produce prolonged viraemia and tissue persistence, but the phrase “persistently infected” needs careful interpretation.

With classical pestiviruses such as bovine viral diarrhoea virus, a truly persistently infected animal is typically immune-tolerant, remains continuously viraemic and sheds virus throughout life.

APPV does not always follow that neat pattern.

The 2026 cohort study found prolonged viraemia alongside measurable APPV antibodies. The researchers did not identify classic virus-tolerant persistently infected pigs, although they could not rule out that such animals might occur under other fetal-infection conditions. (Springer Nature Link)

A separate USDA study followed gilts selected because APPV RNA had persisted in serum during the finishing period. These gilts transmitted APPV to naïve contact pigs during breeding and gestation. Their oral fluids remained positive, but they did not produce congenitally trembling piglets and did not transmit detectable infection to their piglets at farrowing. (ARS)

The practical conclusion is:

Prolonged or intermittent APPV infection occurs, but automatically classifying every repeatedly PCR-positive pig as a lifelong, immune-tolerant PI animal is not currently justified.

How Is APPV Diagnosed?

Diagnosis should combine:

The clinical pattern
The age at onset
Individual RT-qPCR testing
Appropriate tissue selection
Exclusion of other causes

Clinical Pattern

APPV moves higher on the differential list when:

Tremors are present at birth
Several piglets within a litter are affected
Several litters farrow within a short period with similar signs
Tremors increase during voluntary movement
First-parity or newly introduced females are disproportionately affected
Piglets struggle to stand or nurse

The pattern supports APPV but does not confirm it.

RT-qPCR Testing

RT-qPCR can detect APPV RNA in suitable samples.

Useful individual samples may include:

Serum
EDTA whole blood
Cerebellum
Brainstem
Spinal cord
Lymph nodes
Other tissues selected by the diagnostic laboratory

For a live neonatal piglet, individual serum or whole blood is more informative than relying only on a pen-level oral-fluid result.

For dead or humanely euthanised piglets, central nervous system and lymphoid tissues may improve diagnostic confidence. Sampling instructions should be obtained from the laboratory before collection whenever possible.

Oral-Fluid Testing

Oral fluids can demonstrate group-level APPV circulation through nursery or finishing populations.

They cannot reliably determine:

Which pig is infected
Which pig is viraemic
Which pig introduced the virus
Whether congenital disease in a particular litter was caused by that detected strain

Use oral fluids for surveillance, not as the only diagnostic evidence for one affected newborn.

Semen Testing

RT-qPCR can detect APPV RNA in raw semen or AI doses.

A positive result confirms viral RNA, not necessarily infectious virus. A negative serum result from the boar also does not guarantee semen is negative, because localised reproductive-tract shedding may occur without detectable systemic viraemia. (Springer Nature Link)

Genetic Sequencing

APPV is genetically diverse.

In one field outbreak, an existing commercial qPCR assay initially produced negative results. Metagenomic sequencing identified a divergent APPV strain, and a newly designed strain-specific assay subsequently detected the virus in affected animals. Primer mismatches were the likely reason for the earlier false-negative results. (OUP Academic)

When the clinical pattern strongly suggests APPV but routine PCR is negative, discuss:

An alternative RT-qPCR assay
Sequencing
Metagenomic analysis
Testing additional tissues
Resampling very young affected piglets

A single negative assay does not always close the case.

What May Be Found at Post-Mortem Examination?

Gross lesions may be absent.

Histological changes reported in APPV-associated congenital tremor include:

Reduced central nervous system myelination
White-matter vacuolation
Changes in the cerebellum
Changes in the brainstem or spinal cord

However, lesions are variable and are not identified in every confirmed case. A normal-looking brain or an inconclusive histological examination does not exclude APPV. (OUP Academic)

Virus distribution may also change with age. APPV has been detected in neural, lymphoid, glandular and reproductive tissues, and viral RNA may persist after visible tremors improve. (Springer Nature Link)

What Else Can Cause Congenital Tremor?

Congenital tremor in pigs has historically been divided according to cause and pathological findings.

Important differential diagnoses include:

Differential	Important clues
APPV congenital tremor type A-II	Present at birth, action-associated tremor, several littermates affected
Classical swine fever-related congenital tremor	Regulatory concern, systemic or reproductive signs may also occur
Inherited congenital tremor	Repeated association with specific lines or sires
Toxic congenital tremor	Exposure of the dam to recognised toxic compounds during gestation
Congenital tremor type B	Tremor without consistently identifiable myelin lesions
Hypoglycaemia or hypothermia	Weakness, cold body, poor nursing, improvement with stabilisation
Bacterial meningitis or encephalitis	Fever, altered consciousness, paddling or signs beginning after birth
Trauma	Asymmetry, swelling, pain or individual rather than litter-level disease
Porcine sapelovirus, teschovirus or astrovirus	More commonly considered in postnatal or older-pig neurological disease
Splay-leg syndrome	Limb abduction and inability to stand without necessarily having tremor

Genetic and toxic causes remain important when APPV testing is repeatedly negative or the problem consistently follows a particular breeding line, feed source or gestational exposure. (PubMed Central (PMC))

When Is This an Emergency?

Mild congenital tremor in a warm, nursing piglet is not automatically an emergency.

Urgent veterinary assessment is required when piglets have:

Inability to stand
Inability to reach or maintain attachment to a teat
Hypothermia
Marked weakness
Dehydration
Respiratory distress
Blue or pale mucous membranes
Repeated crushing injuries
True convulsions
Altered awareness
Inability to swallow
Rapidly increasing mortality
Several litters suddenly affected

Contact the herd veterinarian immediately when tremor occurs alongside:

Fever
Haemorrhage
Diarrhoea across several age groups
Reproductive failure
Abortions
Oral or skin lesions
Severe systemic disease
Unusual mortality outside the neonatal period

Those findings are not adequately explained by uncomplicated APPV congenital tremor and may indicate a different or concurrent infectious disease.

What To Do Right Now

1. Identify Every Affected Litter

Record:

Sow or gilt identification
Parity
Sire and semen batch
Farrowing date
Total born
Born alive
Stillborn
Mummies
Piglets with tremor
Piglets with splay leg
Preweaning deaths
Cause and timing of each death

A litter-level pattern is far more informative than a note saying “some piglets shook.”

2. Warm and Dry the Piglets

Cold piglets become weak, nurse poorly and are more easily crushed.

Provide a warm, dry creep area with enough space for affected piglets to remain beneath the heat source without being piled beneath stronger littermates.

Do not assume every shaking piglet is cold. APPV tremor may continue after body temperature is corrected, but thermal support remains essential for survival.

3. Confirm Colostrum and Milk Intake

Check whether each piglet:

Reaches the udder
Attaches to a teat
Maintains suction
Develops a full abdomen
Remains warm after feeding
Gains weight

Assist affected piglets to a productive teat repeatedly during the first hours of life.

Split suckling, supervised nursing or carefully planned cross-fostering may be required. Movement between litters should be controlled because apparently normal pigs may also carry APPV and because cross-fostering can spread other pathogens.

4. Reduce Crushing Risk

Piglets with poor coordination may remain close to the sow or fail to escape when she changes position.

Increase farrowing supervision and confirm that:

The creep area is attractive
Flooring provides traction
Piglets can move away from the sow
Weak piglets are not trapped beneath larger littermates
The sow is not unusually restless or aggressive

5. Assess Splay Leg Separately

Use non-slip flooring and have severely affected piglets assessed for supportive limb management.

Splay leg may require temporary physical support, but it should not distract from nursing, temperature and neurological assessment. A piglet may have splay leg without APPV or may have both conditions.

6. Sample Early

The best diagnostic opportunity may be during the first few days of life.

Work with the diagnostic laboratory to collect:

Individual serum or whole blood
Samples from affected and unaffected littermates
Central nervous system tissues from appropriate fresh cases
Lymphoid tissues
Dam samples where relevant
Semen or replacement-animal samples only as part of a defined epidemiological investigation

Do not wait until the only remaining specimens are badly decomposed or heavily treated.

7. Avoid Uncontrolled Feedback

Deliberately feeding fetal material, placental material or tissues back to breeding animals has been used in some field investigations, but APPV exposure timing, dose, concurrent pathogens and consequences are not sufficiently predictable for casual use.

Do not introduce biological material into the breeding herd without veterinary, diagnostic and regulatory oversight.

Is There a Treatment for APPV?

There is no established antiviral treatment that clears APPV from affected piglets.

Treatment focuses on preventing the secondary events that actually kill them:

Hypothermia
Starvation
Dehydration
Crushing
Trauma
Secondary infection

Supportive Care

Appropriate supportive care may include:

Thermal support
Assisted nursing
Colostrum management
Careful supplementation when needed
Frequent weight monitoring
Improved flooring traction
Reduced litter competition
Treatment of secondary bacterial disease
Humane euthanasia when welfare cannot be maintained

Antibiotics do not treat APPV. They are appropriate only when a separate bacterial infection is diagnosed or strongly suspected.

When Should Euthanasia Be Considered?

Humane euthanasia may be the most appropriate decision when a piglet:

Cannot stand despite support
Cannot nurse or swallow safely
Remains severely hypothermic
Has repeated traumatic injuries
Develops severe respiratory compromise
Continues deteriorating despite intensive care
Has no realistic prospect of maintaining an acceptable quality of life

The goal is not simply keeping every affected piglet alive. It is achieving survival with adequate nutrition, warmth, mobility and welfare.

Is There an APPV Vaccine?

No established commercial APPV vaccine is currently available.

Experimental E2-based subunit vaccines have produced immune responses and protection in research pigs, but these remain vaccine candidates rather than routine commercial herd products. Further work is required to establish broad protection across APPV’s considerable genetic diversity and to determine appropriate sow or gilt vaccination programmes. (Frontiers)

This means current herd control depends on:

Surveillance
Replacement management
Semen-source review
Pig-flow management
Early neonatal care
Diagnostic investigation
Reduction of unnecessary animal movement

Can APPV Be Eradicated From a Herd?

There is no universally validated APPV eradication protocol.

Eradication is complicated because:

Apparently healthy pigs may be viraemic.
Tremors do not identify every infected pig.
Infection may persist for months.
Horizontal infection is commonly subclinical.
Serum testing may miss localised semen shedding.
PCR detects RNA rather than necessarily infectious virus.
True lifelong PI status remains incompletely defined.
No commercial vaccine is available.

These limitations mean a standard “30 to 45-day quarantine plus one negative PCR” cannot guarantee APPV freedom. (Springer Nature Link)

A More Defensible Herd-Control Plan

Confirm the diagnosis first

Do not build an elimination programme around tremor alone.

Establish whether APPV is present, whether it matches the clinical syndrome and whether another cause is contributing.

Investigate the breeding pathway

Review:

Gilt source
Gilt-isolation records
Boar or semen source
Semen batch records
Parity distribution of affected litters
Timing of APPV detection
Genetic relationships between viral sequences where available

High sequence similarity can support an epidemiological link but does not prove direction of transmission.

Use risk-based replacement isolation

Incoming gilts should undergo a herd-specific isolation and testing plan designed with the veterinarian and laboratory.

Because APPV infection can be transient, prolonged or intermittent, the plan may require:

More than one sample
More than one sample type
Sampling at defined intervals
Testing before entry into the breeding herd
Interpretation alongside source-herd history

There is no universally accredited “APPV-free” replacement standard.

Review semen risk realistically

Purchase semen from suppliers with transparent health monitoring and APPV policies where available.

Routine PCR testing of every AI dose cannot currently be presented as a scientifically validated universal prevention standard. Infectivity, infectious dose and venereal-transmission efficiency remain unresolved. (Springer Nature Link)

Maintain structured pig flow

Use:

Age segregation
All-in, all-out movement where practical
Cleaning between groups
Dedicated equipment
Controlled cross-fostering
Reduction of backwards pig movement
Clear separation of isolation, breeding and production units

These measures cannot guarantee APPV exclusion, but they reduce uncontrolled horizontal circulation and help with many other swine pathogens.

What Is the Prognosis?

Individual Piglets

The prognosis is more favourable when the piglet:

Can stand
Can nurse
Maintains body temperature
Gains weight
Avoids crushing
Shows improvement during the first days or weeks

The prognosis becomes guarded when tremor prevents normal feeding or movement.

A piglet may improve clinically while remaining viraemic, so recovery should not be interpreted as proof that the piglet is no longer involved in transmission. (Springer Nature Link)

Affected Litters

Litter outcome depends heavily on:

Proportion affected
Severity
Staffing
Farrowing supervision
Colostrum management
Flooring
Sow behaviour
Cross-fostering
Concurrent disease

Mortality estimates from one severe outbreak should not be copied into every herd forecast.

Future Farrowings

Outbreaks often affect gilts or naïve females more heavily than older sows, consistent with protective immunity developing after exposure. However, this pattern is not absolute, and APPV-positive adult animals do not invariably produce affected offspring. (Springer Nature Link)

Common APPV Mistakes

Saying 98.9% of Semen Was Positive

The figure represented nucleotide identity between two APPV sequences, not semen-sample prevalence.

Assuming Positive Semen Proves AI Transmission

APPV RNA is found in semen, but infectious venereal transmission remains to be confirmed experimentally.

Blaming Every Splay-Leg Piglet on APPV

APPV may be associated with splay leg in some affected litters, but naturally occurring splay leg has several causes.

Testing Only One Piglet

APPV status and tremor severity vary within litters. Sample affected and unaffected littermates where possible.

Relying on One Negative PCR Assay

APPV genetic diversity can produce assay mismatch and false-negative results.

Assuming No Tremor Means No Virus

Clinically normal pigs may remain viraemic and contribute to horizontal transmission.

Calling Every Repeatedly Positive Pig a Classic PI Animal

Prolonged APPV infection occurs, but classic lifelong immune-tolerant persistent infection has not been demonstrated consistently.

Treating With Antibiotics Alone

Antibiotics do not treat APPV or reverse congenital neurological dysfunction.

Waiting Until Piglets Are Cold and Empty

The most useful intervention is early support of warmth, colostrum and milk intake.

Promising Eradication Through One Quarantine Period

No universal test-and-removal protocol currently guarantees APPV elimination.

How Can Future Losses Be Reduced?

Train Farrowing Staff To Recognise Birth-Onset Tremor

Staff should distinguish:

APPV-type action tremor
Cold shivering
Hypoglycaemic weakness
True seizures
Splay leg
Traumatic injury

Record signs before affected piglets are extensively moved or treated.

Build a Neonatal Rescue Protocol

The protocol should cover:

Immediate drying
Thermal support
Colostrum access
Assisted teat attachment
Split suckling
Cross-fostering criteria
Weight monitoring
Crushing prevention
Euthanasia criteria

Track APPV by Parity and Source

Record whether affected litters are associated with:

Incoming gilts
First-parity females
Particular genetic groups
Particular semen sources
Specific farrowing batches
Specific buildings or pig flows

This helps separate one introduction event from ongoing farm circulation.

Maintain a Diagnostic Sample Plan

Before an outbreak occurs, identify:

The diagnostic laboratory
Preferred live-animal samples
Preferred post-mortem tissues
Storage and transport requirements
The available RT-qPCR assays
Sequencing options after unexpected negative results

Review the Herd Plan After Every Outbreak

Compare:

Affected-litter prevalence
Piglet mortality
Parity
Viral sequences
Replacement introductions
Semen batches
Nursery and finisher surveillance
Clinical recurrence

The objective is not collecting APPV data for decoration. It is determining where intervention is most likely to reduce the next farrowing loss.

Frequently Asked Questions

Is APPV fatal to piglets?

APPV is not invariably fatal. Most deaths are secondary to impaired nursing, hypothermia, crushing, dehydration or associated weakness. Mildly affected piglets may survive and improve.

Does APPV always cause splay leg?

No. Splay leg may be more common in some APPV-affected litters, but it is multifactorial and occurs without APPV.

Can APPV spread through semen?

APPV RNA can be present in semen, and semen is considered a plausible transmission route. Infectious transmission through artificial insemination has not yet been experimentally confirmed.

Can a healthy-looking pig spread APPV?

Yes. Clinically normal littermates and older pigs may be viraemic, and tremor status does not reliably identify infectious animals. (Springer Nature Link)

Is there a vaccine or cure?

There is no established commercial vaccine or antiviral cure. Current treatment is supportive, while experimental APPV vaccine candidates remain under investigation. (Frontiers)

Final Thoughts

APPV is now firmly established as a cause of congenital tremor type A-II, but important gaps remain in its transmission and control.

The most important points are:

APPV is currently classified as Pestivirus scrofae.
It was first identified in North America in 2015.
Fetal infection can cause congenital tremor at birth.
Tremors commonly become more obvious during voluntary movement.
Severe piglets die mainly because they cannot nurse, stay warm or avoid crushing.
Mildly affected piglets may improve over days or weeks.
Clinical recovery does not guarantee virological clearance.
Apparently normal pigs may remain viraemic.
Splay leg can accompany APPV but is not specific to the virus.
APPV RNA has been found in semen, but AI transmission remains unconfirmed.
The 98.9% figure referred to viral sequence identity, not semen positivity.
RT-qPCR is central to diagnosis, but assay mismatch can cause false-negative results.
Oral fluids are useful for group surveillance but do not identify individual infected pigs.
Prolonged infection occurs, but classic lifelong PI status remains incompletely resolved.
There is no universally validated APPV eradication programme.
There is no established commercial vaccine.
Neonatal warmth, nursing support and crushing prevention remain the most important immediate interventions.
Several affected litters should trigger a full breeding, semen, replacement and pig-flow investigation.

The mistake that causes the greatest losses is treating APPV as nothing more than a shaking-piglet problem. What matters is whether affected piglets can nurse and survive, where the virus entered the breeding system and how widely it is circulating without visible signs.

ASK A VET™ can help organise affected-litter records, parity patterns, semen and replacement histories, diagnostic results and neonatal-support observations while producers work directly with their herd veterinarian and swine diagnostic laboratory. Piglets that cannot stand, nurse, remain warm or swallow safely still require immediate hands-on veterinary care.

Know how they are, wherever they are

The ASK A VET™ Tracker logs live location and activity trends, so a change in routine never goes unnoticed.

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About the author

Dr Duncan Houston

Veterinarian · Founder of ASK A VET

Every ASK A VET article is written and reviewed by qualified veterinarians.

About Dr. Duncan →drduncanthevet

Atypical Porcine Pestivirus in Piglets: Congenital Tremor, Diagnosis and Herd Control