CLASSICAL SWINE FEVER VIRUS (CSFV)
LEVELS: Highly unlikely: No controls necessary; Highly unlikely: No evidence of non-foodborne zoonotic transmission; Unlikely to be effective: One or more pathways of farm-to-farm transmission exist that cannot be controlled by on-farm biosecurity; Moderate: Clinical signs not unique but existing tests available at local/regional laboratory(s); Substantial: Unsustainable acute or chronic losses related to severe clinical signs in a high prevalence of animals; Prolonged disruption: Measureable negative effect on demand for more than 6 months when disease occurs on one or more farms; Minimal risk: Agent inherently unlikely to develop clinically important resistance to antibacterial or antiviral treatments; Minimal risk: Antibacterial or antiviral treatments rarely occur, or are typically limited to short-course individual animal therapy; No availability: Effective treatments not currently available in the US (or have not been developed); Widely available: Effective commercial vaccines widely available in the US (or held in national response stockpile); Highly likely: Can be eradicated using existing tools and knowledge
OVERVIEW
Classical swine fever (CSF), formerly known as "hog cholera," is a highly contagious viral disease caused by Classical Swine Fever Virus (CSFV), a pestivirus in the family Flaviviridae. CSF is one of the World Organisation for Animal Health (WOAH)-listed diseases and represents one of the most economically important diseases of swine worldwide. Wild and domestic pigs are the only natural reservoirs of CSFV. The virus is endemic in parts of Southeast Asia, Central America, the Caribbean, and South America, while Australia, New Zealand, North America, and most European countries are currently CSFV-free. Japan experienced reemergence in 2018 after 26 years of freedom. CSFV is genetically diverse with three major genotypes, each containing multiple subgroups, though there is only one serotype with cross-protection between strains. Clinical presentation varies from acute hemorrhagic disease with high mortality (highly virulent strains) to chronic wasting with immunosuppression (moderately virulent strains), and includes reproductive failure with persistently infected piglets ("carrier sow syndrome"). The disease is notoriously difficult to diagnose clinically as it produces no pathognomonic signs and can resemble many other conditions including PRRS, African swine fever, and salmonellosis. Control in free countries relies on early detection and stamping out, while endemic areas use vaccination. Multiple effective vaccines exist including modified live virus vaccines (C strain), E2 subunit marker vaccines enabling DIVA (Differentiate Infected from Vaccinated Animals), and newer chimeric vaccines. Wild boar serve as a significant reservoir complicating eradication efforts in affected regions.
FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No controls necessary
The chapter explicitly states: "There is no evidence of human infection with pestivirus, and they are not of any significance for public health or food safety." CSFV is strictly a pathogen of suids (pigs, wild boar, and other members of family Suidae). Despite over a century of recognition and extensive global circulation, no human infections have ever been documented. The virus poses no foodborne risk to consumers of pork products.
NON-FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No evidence of non-foodborne zoonotic transmission
CSFV does not infect humans through any route. Veterinarians, farm workers, slaughterhouse personnel, and laboratory workers handling infected animals and tissues have never been documented to develop infection. The virus has an extremely narrow host range restricted to members of family Suidae (domestic pigs, wild boar) and possibly family Tayassuidae (peccaries, based on limited evidence). No public health precautions beyond standard biosecurity are required when handling CSFV-infected materials.
EFFECTIVENESS OF ON-FARM BIOSECURITY IN PREVENTING FARM-TO-FARM TRANSMISSION
Level: Unlikely to be effective: One or more pathways of farm-to-farm transmission exist that cannot be controlled by on-farm biosecurity
CSFV is highly contagious and spreads efficiently despite biosecurity measures. Primary transmission is oronasal through direct or indirect contact with infected pigs, or oral via contaminated feed. The virus spreads rapidly within affected holdings and can transmit via multiple pathways that challenge biosecurity: (1) Movement of infected pigs (accounts for majority of outbreaks in finishing units); (2) Vehicles transporting contaminated feces and urine over long distances; (3) Contaminated fomites (boots, clothing, equipment); (4) Airborne transmission demonstrated experimentally over short distances; (5) Semen from infected boars; (6) Contaminated feed, especially swill containing infected pork products. The virus survives for prolonged periods under cool, moist, protein-rich conditions—2 weeks at 20°C and more than 6 weeks at 4°C in liquid manure. Wild boar serve as a reservoir, with 52% of European outbreaks attributed to transmission from wild boar. Chronically and persistently infected pigs shed high quantities of virus continuously for extended periods, serving as critical transmission sources. Mathematical models confirm that even with movement restrictions, CSFV spreads efficiently within pig-dense areas.
DIFFICULTY OF DETECTING AND CONFIRMING INFECTION
Level: Moderate: Clinical signs not unique but existing tests available at local/regional laboratory(s)
CSFV produces no pathognomonic clinical signs, making early detection challenging. Clinical presentation varies with strain virulence, animal age, and immune status. Moderately virulent strains (genotype 2, now most prevalent) cause mild, transient disease easily confused with PRRS, postweaning dermatitis and nephropathy syndrome (PDNS), salmonellosis, coumarin poisoning, or African swine fever. The "carrier sow syndrome" with persistently infected piglets further complicates detection. However, once CSF is suspected, laboratory confirmation is straightforward using well-established methods. Real-time RT-PCR is the preferred method—rapid, highly sensitive and specific, with multiple validated protocols and commercial kits available. Virus isolation in porcine kidney cells (PK-15, SK6) confirms infection but is labor-intensive and time-consuming. Antigen-capture ELISA provides rapid results but has lower sensitivity than RT-PCR. Serology (virus neutralization test, ELISA) is useful when clinical signs have been present >2 weeks, as viremia is relatively short. Cross-reactions with BVDV and BDV antibodies require differential testing using comparative virus neutralization. Preferred samples include tonsil, spleen, ileum, lymph nodes, and whole blood (EDTA, not heparin). Population-based sampling using oral fluids has been validated for surveillance.
FINANCIAL IMPACT ON FARM'S COST OF PRODUCTION
Level: Substantial: Unsustainable acute or chronic losses related to severe clinical signs in a high prevalence of animals
CSF outbreaks cause catastrophic losses through multiple mechanisms. Direct mortality varies with strain virulence—highly virulent strains (Koslov, Shimen) cause severe, usually lethal disease in all ages within days; moderately virulent strains cause 14-25 day disease courses with variable mortality. Young animals are most severely affected. Reproductive losses are substantial: the "carrier sow syndrome" produces persistently infected, immunotolerant piglets that appear initially normal but develop "late onset CSF" with wasting and high mortality. Abortion, fetal mummification, stillbirths, and congenital malformations occur. CSFV-induced immunosuppression leads to severe secondary infections (respiratory, gastrointestinal) that compound losses. Beyond direct disease costs, control measures impose massive economic impact: stamping out requires culling of entire infected and suspect herds; movement restrictions in pig-dense areas can force euthanasia of large numbers of healthy animals unable to move to slaughter (as occurred in the 1997 Netherlands outbreak); cleaning and disinfection costs are substantial. The 1997-1998 Netherlands epidemic resulted in the destruction of over 11 million pigs. Endemic circulation in affected regions imposes ongoing production losses and control costs.
EFFECT ON DOMESTIC OR EXPORT MARKETS
Level: Prolonged disruption: Measureable negative effect on demand for more than 6 months when disease occurs on one or more farms
CSFV is a WOAH-listed disease with severe trade implications. Detection in a previously free country triggers immediate regulatory response: notification to WOAH, implementation of control zones, suspension of international trade in pigs and pork products. Trading partners impose precautionary restrictions that can extend well beyond affected regions. The "no vaccination" policy maintained by free countries for trade purposes means that if emergency vaccination is used, vaccinated areas face trade bans for at least one year even after virus elimination. Market access restoration requires extensive surveillance, demonstration of freedom, and international recognition—a process taking years. Endemic countries face permanent exclusion from premium export markets. Consumer confidence impacts can extend beyond directly affected products. The economic consequences of the 1997-1998 European epidemics (Netherlands, Germany, Belgium) demonstrated the catastrophic market impacts: billions of euros in losses, with effects persisting for years after eradication. Japan's 2018 reemergence after 26 years of freedom illustrates the ongoing risk of market disruption even for countries with long-established freedom.
PATHOGEN'S ABILITY TO DEVELOP AND SPREAD RESISTANCE
Level: Minimal risk: Agent inherently unlikely to develop clinically important resistance to antibacterial or antiviral treatments
CSFV is a viral pathogen (positive-sense single-stranded RNA virus) that does not carry, acquire, or transmit antimicrobial resistance genes. The virus poses no AMR concerns. CSFV is relatively stable for an RNA virus, with genetic diversity organized into three genotypes and multiple subgroups. Recombination between strains is theoretically possible but has not been reported in the field. Antigenic variation exists between strains, but there is sufficient cross-protection that a single serotype is recognized and vaccines based on one strain protect against heterologous challenge.
AMR DEVELOPMENT DRIVEN BY DISEASE MANAGEMENT
Level: Minimal risk: Antibacterial or antiviral treatments rarely occur, or are typically limited to short-course individual animal therapy
No antiviral treatments exist for CSFV. The primary management approaches are prevention (vaccination in endemic areas) and eradication (stamping out in free areas)—neither involves antimicrobial use. Antimicrobials may be used to treat secondary bacterial infections that occur due to CSFV-induced immunosuppression, but this represents episodic, individual animal treatment rather than systematic herd-level use. In stamping-out programs, infected animals are culled rather than treated, eliminating any antimicrobial selection pressure.
AVAILABILITY OF EFFECTIVE TREATMENT OPTIONS
Level: No availability: Effective treatments not currently available in the US (or have not been developed)
No specific antiviral treatments exist for CSFV infection. Management is entirely preventive (vaccination) or reactive (stamping out). Pigs that recover from acute infection do so through their own immune response. Chronically and persistently infected animals cannot clear the virus and eventually die. Supportive care and treatment of secondary infections may reduce mortality in some cases but does not address the underlying viral infection. In free countries pursuing eradication, treatment is not attempted—infected and suspect animals are culled.
AVAILABILITY OF EFFECTIVE VACCINES OR BACTERINS
Level: Widely available: Effective commercial vaccines widely available in the US (or held in national response stockpile)
Multiple highly effective CSFV vaccines are available: (1) Modified live virus (MLV) vaccines including the "Chinese" C strain and Thiverval strain provide rapid, robust protection. The C strain induces protective immunity within 10 days (even orally), with duration of 6-10 months regardless of administration route. Cross-protection exists between genotypes. The primary limitation is inability to serologically differentiate vaccinated from infected animals. (2) E2 subunit marker vaccines (baculovirus-expressed E2 protein) enable DIVA through companion Erns-ELISA testing. A single dose prevents clinical signs and mortality when challenged 3 weeks post-vaccination, though at least 14 days are needed for protection. These vaccines protect against clinical disease but may not prevent horizontal or vertical transmission, limiting their ability to prevent the "carrier sow syndrome." (3) Chimeric pestivirus vaccines (CP7_E2Alf) represent the newest generation—safe, highly immunogenic, effective by oral or intramuscular routes, and enable serological DIVA. This vaccine could be used for emergency vaccination in domestic pigs or oral vaccination of wild boar. Maternal antibodies provide piglet protection for 8-12 weeks but can interfere with vaccination response.
FEASIBILITY OF ERADICATING THE DISEASE FROM THE US
Level: Highly likely: Can be eradicated using existing tools and knowledge
The United States successfully eradicated CSFV and has maintained freedom since 1978. Multiple other countries have achieved and maintained CSFV-free status, including Canada, Australia, New Zealand, and most of Europe. Eradication tools are well-established: early detection through clinical surveillance and laboratory testing; stamping out of infected and contact herds; movement restrictions and quarantine; cleaning and disinfection of premises; epidemiological tracing; and serological surveillance to demonstrate freedom. If CSFV were reintroduced to the US, eradication would follow established protocols with high likelihood of success, provided detection occurs early before widespread dissemination. Key challenges include: (1) Early detection given non-specific clinical signs; (2) Pig-dense areas where rapid spread can outpace control measures; (3) Feral swine populations that could establish a wildlife reservoir if infected. Emergency vaccination could be deployed to slow spread in outbreak situations, though this complicates trade restoration. The availability of DIVA vaccines and companion diagnostics improves the feasibility of vaccination-to-live strategies while maintaining ability to demonstrate freedom. Wild boar reservoirs have complicated eradication in parts of Europe, highlighting the importance of preventing feral swine infection.