Classical Swine Fever (Hog cholera)

Key takeaways 

• Highly contagious viral disease: CSF (hog cholera) is an acute, often fatal, notifiable viral disease of pigs caused by an enveloped Pestivirus (Flaviviridae). It has one serotype with multiple genetic groups. 

• Clinical signs: Infected pigs develop high fever, lethargy and anorexia, often followed by diarrhoea, vomiting, respiratory distress, haemorrhages (purple skin discoloration on ears, abdomen, limbs) and neurological symptoms. Young pigs and boars experience reproductive losses (abortions, stillbirths). 

• Transmission routes: CSF spreads via direct contact (infected pigs’ secretions/excretions) or indirect contact (contaminated feed/swills, equipment, vehicles, fomites). Wild boar serve as reservoirs and can transmit CSF to domestic herds. Importation of infected pork or contaminated feed is a key risk. 

• No treatment – prevention by control: There is no cure for CSF. Control relies on strict biosecurity and sanitary measures (farm isolation, disinfection), rapid detection, and stamping-out (culling) of affected herds. In endemic regions, vaccination (live attenuated or marker vaccines) is used to prevent spread, but vaccinated animals must be distinguishable from infected ones (DIVA). 

• Global distribution & impact: CSF is endemic in parts of Asia, Latin America and the Caribbean, while many countries (North America, Australia, New Zealand, most of Western Europe) are CSF-free. Large outbreaks can devastate production. CSF remains a major concern for pig producers and vets worldwide due to its economic threat. 

Causes and classification of Classical Swine Fever

Classical Swine Fever virus (CSFv) is a small, enveloped positive-sense RNA virus in the genus Pestivirus of the family Flaviviridae. It is closely related to bovine viral diarrhoea virus and border disease virus in sheep, but CSFv is specific to pigs (domestic swine and wild boar). Only one serotype of CSFv exists, although several genetic lineages (genotypes) are recognised. Recent phylogenetic work divides CSFv into up to 5 genotypes with multiple sub-genotypes; for example, genotypes 1 and 2 are widespread, with genotype 2 strains (including subtypes 2.1–2.7) currently dominant in many regions. Typically, genotype 1 strains are associated with more severe disease, while genotype 2 strains are often moderately virulent. 

Pestiviruses like CSFv are enveloped and acid labile; CSFv survives weeks to months in chilled pork and even years in frozen meat products. The virus can be transmitted globally via international trade in live pigs or pork products. Because of its severity, CSF must be reported to the World Organisation for Animal Health. 

Clinical Signs & Diagnosis of Classical Swine Fever

CSF can present in peracute, acute, chronic or subclinical forms, depending on the virus virulence and herd immunity. In the acute form, pigs of all ages develop high fever (often >40 °C) that lasts until terminal stages, followed by prostration and death within 1–2 weeks. Common signs include lethargy and huddling, conjunctivitis, anorexia, constipation followed by haemorrhagic diarrhoea and vomiting. A characteristic finding a few days into infection is red-blue (purple) discolouration of the skin on the ears, belly and inner thighs. Neurological signs (ataxia, tremors, convulsions) may occur late. Mortality in an acute herd outbreak can approach 100% if the strain is highly virulent. 

Less virulent strains cause chronic CSF: poor reproduction, intermittent fever, stunting and poor growth, with occasional relapses of fever. Pregnant sows exposed early in gestation may suffer foetal death, mummifications or give birth to persistently infected piglets (which shed virus without external signs). Pigs surviving chronic CSF often have prolonged immunosuppression (lymphoid depletion). 

Because CSF clinical signs overlap with other diseases (notably African swine fever, porcine erysipelas, septicaemia, salmonellosis etc.), laboratory confirmation is essential. Diagnosis relies on detecting the virus or antibodies. Common tests include RT-PCR to detect CSFV RNA in blood or tissues, virus isolation or antigen ELISA, and serological assays (ELISA or virus neutralization) to detect antibodies. PCR is widely used for rapid confirmation. Testing laboratories follow WOAH protocols (Terrestrial Manual) for CSF diagnostics. In practice, any fever + haemorrhagic syndrome in pigs triggers immediate sampling and quarantine, with samples sent to approved labs for CSFV PCR/ELISA confirmation. 

Transmission & risk factors of Classical Swine Fever

CSF virus is transmitted very efficiently among pigs. The most important route is direct contact: infected pigs shed virus in saliva, nasal secretions, urine and faeces, and susceptible pigs become infected by inhaling the virus or contacting contaminated excretions. Contaminated fomites (clothing, footwear, vehicles, equipment), as well as semen from infected boars, can carry the virus. Feeding pigs swill or kitchen scraps containing uncooked pork from infected animals is a well-known risk factor. CSFv is hardy in cold meat, so even frozen pork products can be a source. 

Wild boar and feral pigs play a key role in maintenance of CSF, especially in Europe and parts of Asia. Infected wild boar can infect domestic pigs (and vice versa) via direct or indirect contact (e.g. shared pasture, water sources). Outbreaks have repeatedly been linked to wild pig populations (e.g. Germany and Belgium in the 1990s; wild boar vaccination campaigns show the role of wildlife). 

Risk factors for introduction of CSF into a farm include: importing pigs or pork from endemic areas, lax biosecurity, swill feeding and visits by contaminated vehicles or people. Commercial farms often have many truck and worker contacts, increasing risk if biosecurity lapses. Smallholder/backyard farms may have looser biosecurity (feeding waste, less quarantine), also raising risk. In CSF-free countries, illegal imports of pork or uncooked pork products pose a major threat. Overall, any lapse that allows infected material or animals into a herd can spark an outbreak, given CSFv’s contagiousness. 

Control & prevention of Classical Swine Fever

There is no treatment or cure for CSF; management focuses on prevention and rapid containment. The cornerstone of CSF control is strict biosecurity. All farms must prevent contact between their pigs and unknown swine or wild boar, disinfect vehicles and equipment, control farm access and prohibit swill feeding. Surveillance systems (reporting feverish pigs, regular testing in high-risk zones) are critical. Good communication between farmers and veterinary authorities ensures suspicions trigger rapid response. 

If CSF is diagnosed in a herd, immediate stamping-out is mandated: all pigs on the affected farm (and usually on epidemiologically linked farms) are humanely culled, with safe disposal of carcasses and thorough decontamination. A quarantine zone is established around the outbreak site to monitor and test surrounding herds. Movement controls for live pigs and pork products are imposed. No pork from the affected area may enter trade. This aggressive approach has eradicated CSF in many regions in the past (e.g. North America and Western Europe). 

In regions where CSF is endemic, vaccination is a key preventive tool. Licensed live attenuated vaccines (such as the C-strain and others) induce strong immunity and prevent spread if coverage is high. These vaccines are very effective but induce antibody responses identical to natural infection, so vaccinated animals cannot be serologically distinguished from survivors of wild virus exposure. Therefore, “DIVA” (Differentiating Infected from Vaccinated Animals) strategies are under development (see next section). Vaccination campaigns for wild boar (oral bait vaccines) have also been used in Europe to reduce wildlife reservoirs. 

Internationally, CSF control is coordinated under WOAH standards. Countries or zones meeting surveillance and biosecurity criteria can be officially recognised as CSF-free. Movement of pigs and pig products from free areas is then more easily permitted, while trade bans apply when outbreaks occur. In summary, prevention hinges on preventing virus entry (biosecurity), and eradication relies on prompt stamping-out and, where needed, strategic vaccination. 

Farm management of Classical Swine Fever: Smallholder vs commercial 

Small-scale/backyard and commercial pig farms differ in resources, scale and husbandry, affecting CSF risk. Commercial farms typically house larger pig populations and have more intensive production (farrow-to-finish or multiple sites). They tend to employ more staff and have frequent contacts (trucks, workers, service providers), as one study in Indonesia found: commercial farms had 2–3 times the daily person/vehicle contacts compared to smallholders. This greater contact network can amplify the risk of introducing CSF if biosecurity slips (more movement of animals, semen, feed trucks etc.). However, commercial operations usually have higher biosecurity standards (disinfection, fencing, controlled entry points) and may vaccinate routinely in endemic areas. 

By contrast, smallholder and backyard farms often keep pigs for local sale or subsistence. These farms may have looser biosecurity: pigs might be left free-range, fed untreated swill or garbage, and rearing pens may lack secure fencing. Veterinary oversight can be minimal, and animal health reporting may be delayed. In CSF-endemic countries, many smallholders vaccinate irregularly or not at all due to costs. The contact study noted that smallholders had fewer outside contacts (trucks, market trips) than commercial farms, which might slow disease spread, but their lower biosecurity can still permit outbreaks. 

Both farm types can benefit from good management: in all settings, keeping pigs indoors or fenced, providing clean feed (no swill), isolating new stock, and limiting visitors are critical. Commercial units may enforce quarantine for new pigs and require all-in/all-out production cycles, which help break transmission chains. Smallholders should avoid swill and practice simple hygiene measures (footbaths, separate clothes for pig areas). Ultimately, whether small or large, diligent biosecurity and prompt disease reporting are key to preventing and controlling CSF on farms. 

Vaccines and research on Classical Swine Fever

Vaccination is central to controlling CSF in endemic settings. Traditional vaccines are live attenuated (e.g. Chinese “C-strain”, European “GPE–” strain, and various lapinised or cell-culture-based vaccines). These vaccines confer robust immunity and have been used for decades to prevent disease. However, because they induce antibodies identical to those from wild-type infection, they cannot be used in “free” countries without DIVA capability. 

To address this, marker vaccines are a research focus. One such vaccine allows differentiation of infected vs vaccinated pigs by serology (DIVA). Recent studies have engineered additional marker vaccines by deleting viral epitopes or genes and inserting serological tags.  

Aside from live vaccines, subunit and vectored vaccines are under development. In general, current research targets vaccines that are safe (even in pregnant pigs), provide early protection, and allow DIVA testing. 

On the diagnostic side, advanced molecular tools (real-time PCR, high-throughput sequencing) are improving detection speed and surveillance of CSFv variants. Biosecurity innovations (rapid pen-side tests, improved disinfection products) are also being explored.  

Global occurrence & history of Classical Swine Fever

The first descriptions of hog cholera date from the early 19th century: the disease was first reported in 1833 on a pig farm in Ohio, USA. CSF then became enzootic in Europe, Asia and the Americas. Systematic control programmes (e.g. strict culling, movement controls and, where allowed, vaccination) gradually eliminated CSF from much of North America, Australasia and Western Europe by the late 20th century. Table below highlights key historical events: 

Currently, CSF remains endemic in parts of Asia (e.g. China, Southeast Asia, India), Central/South America (e.g. parts of Peru, Colombia) and the Caribbean. Wild and feral pigs perpetuate the virus in some regions. Major CSF-free zones include the United States, Canada, Australia, New Zealand, the European Union (many member states), Japan (officially regained free status in 2023) and several Latin American zones. Outbreaks anywhere carry significant trade implications, so global surveillance (via WOAH’s WAHIS and national reporting) tracks CSF status continuously. 

Frequently asked questions on Classical Swine Fever

Q: What animals are affected by Classical Swine Fever, and can humans catch it? 

A: Only pigs (domestic swine and wild boar) are susceptible to CSF. The virus does not infect other species, and humans are not at risk. Therefore, CSF is strictly an animal health issue. Wild boar populations can serve as a reservoir, so interactions between wild and farmed pigs are a key concern for transmission. 

Q: How is CSF diagnosed in the field, and how is it distinguished from African swine fever? 

A: Diagnosis of CSF cannot rely on clinical signs alone because acute CSF resembles African swine fever (ASF) – both cause fever, haemorrhages and high mortality. Definitive diagnosis requires laboratory tests. PCR (RT-PCR) is used to detect CSFV RNA rapidly in blood or tissues. Antigen-capture ELISAs and virus isolation can confirm active infection. Serology (ELISA or virus neutralisation) detects CSFV antibodies to establish exposure. In practice, any suspected case prompts immediate sample submission to reference labs. ASF is ruled out or confirmed by separate tests. A WOAH-recommended panel of tests is used to tell these diseases apart. 

Q: How does CSF spread on a pig farm, and what are the biggest risk factors? 

A: CSF spreads very efficiently within a farm via nose-to-nose or other close contact. Shared airspace, feeding troughs or water sources can transmit virus between pens. Humans can mechanically carry the virus on hands, boots or clothing if hygiene is poor. Feeding uncooked swill containing infected pork is a classic risk factor that has caused outbreaks. Infected vehicles or equipment (e.g. transport trucks, needles) can also introduce CSFv. Farms near wild boar are at higher risk due to potential wildlife contact. Large farms with frequent pig movements (sales or breeding exchanges) have higher introduction risk, whereas smallholders may have fewer contacts but often lower biosecurity. The key factors are introduction of infected material and failure of hygiene controls. 

Q: What measures should a farm take if CSF is suspected or confirmed? 

A: Suspected CSF is a veterinary emergency. The farm should isolate affected pigs and immediately notify veterinary authorities. Samples are taken for lab confirmation. If CSF is confirmed, all pigs on the premises (and often on linked farms) must be humanely culled (stamping-out), with safe disposal (burial or incineration) and thorough disinfection of facilities. A quarantine zone is established around the affected farm to restrict animal movements and conduct surveillance. Contact tracing identifies at-risk farms. Because no treatment exists, culling and strict biosecurity are the only effective responses. Internationally, affected areas may lose export markets until declared free again. 

Q: Are there effective vaccines against CSF, and how are they used? 

A: Yes, several live-attenuated CSF vaccines have long been used in endemic countries. These vaccines (e.g. C-strain, Lapinised Chinese strain, others) are very effective at preventing disease when administered properly. They stimulate strong immunity that protects pigs from infection and reduces virus shedding. However, these “conventional” vaccines do not allow differentiation of vaccinated vs infected animals (no DIVA), so they are generally only used where CSF is common. In free countries, vaccination is typically prohibited for trade reasons. 

Recent research has produced marker (DIVA) vaccines. For example, one marker LAV (based on the Pestivirus backbone) allows serological distinction of vaccinated pigs. New candidates involve precise gene deletions or epitope changes in CSFV to serve as vaccine strains with built-in markers. Subunit vaccines (using the viral E2 protein) and vectored vaccines (e.g. adenovirus or poxvirus vectors carrying CSF genes) are also under study. These aim to be safe and produce immunity without the need for live virus. In all cases, vaccinated herds must be monitored with companion diagnostics to ensure any field infection can be detected. 

Q: How does CSF status affect international trade and farm policies? 

A: CSF is OIE-notifiable and carries major trade implications. If a country or zone is declared CSF-free, it enjoys access to export markets for pigs and pork. An outbreak (even a single farm) usually triggers trade bans on pigs and pork from the region until the disease is controlled and freedom is reinstated. For this reason, many CSF-free countries (like USA, Canada, EU members, Japan) invest heavily in surveillance and rapid response. Zones may be officially recognised as “CSF-free with or without vaccination” by WOAH if they meet stringent criteria. Farms in free countries often practice very strict biosecurity (no swill feeding, imported pork tightly controlled) to prevent introduction. In contrast, endemic countries focus on internal control (vaccination, culling) but face ongoing trade restrictions. In summary, maintaining a CSF-free status is a high priority for national pig industries. 

Q: What is the difference between Classical Swine Fever and African Swine Fever? 

A: Although CSF (“hog cholera”) and African Swine Fever (ASF) cause similar symptoms in pigs (high fever, hemorrhages, high mortality), they are entirely different viruses. CSF virus is a Pestivirus (Flaviviridae), while ASF virus is an Asfarvirus (a DNA virus) and does not infect humans. Control measures (culling, biosecurity) are similar, but there are no cross-protective vaccines. Important diagnostic difference: ASF often causes more severe bleeding and can be diagnosed by PCR specific for the Asfarvirus. Because of symptom overlap, any hemorrhagic pig disease must be tested for both CSF and ASF to guide control. In practice, veterinarians treat CSF and ASF as separate reportable diseases, each requiring immediate response. 

Q: Can classical swine fever reappear in a CSF-free country, and how? 

A: Yes. A CSF-free status can be lost if the virus is reintroduced. Reintroduction can occur via illegal importation of infected pigs or pork, breaches in biosecurity (e.g. someone bringing contaminated meat into a farm), or migrating infected wild boar. The re-emergence in Japan in 2018, after 26 years of freedom, illustrates this risk (likely due to illegal pork product or wild boar). Once introduced, CSF can spread rapidly if not contained. That is why even countries free of CSF remain vigilant with strict import controls (often requiring foreign pork to be cooked) and surveillance of swine populations. Maintaining freedom requires continuous enforcement of biosecurity and monitoring compliance with WOAH standards.