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Classical Swine Fever

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Classical Swine Fever


Classical swine fever (also known as hog cholera) is a highly contagious viral infection of swine that is often fatal.  The virus is most often transmitted through the ingestion of contaminated feed or garbage. However, the virus may also be spread through open wounds and mucous membranes, contact with bodily secretions or feces of an infected pig, physical transfer from a contaminated object, human or insect, sow to piglet transfer or inhalation in close quarters.


There are three forms of CSF: acute, chronic and mild.  The clinical signs of the acute form of CSF may include:


  • Persistent high fever
  • Weakness
  • Lethargy
  • Ataxia (incoordination)
  • Huddling
  • Anorexia (unwillingness to eat)
  • Conjunctivitis (Pink-eye)
  • Constipation and/or diarrhea
  • Reddish/purplish discoloration of the skin of the abdomen, inner thighs and ears


The acute form of CSF progresses rapidly once clinical signs have begun and death usually occurs within 1-2 weeks with mortality approaching 100%. Click here to view photos of swine with CSF.


The clinical signs of the chronic form of CSF are the same as the acute form but are intermittent instead of persistent.  However, chronic CSF infection may weaken the pig’s immune system making it susceptible to a variety of other infections. Swine infected with the chronic form of the disease may live for months but almost always succumb to the disease.


Swine with the mild form of CSF may not have any clinical signs of disease.  These swine will persistently shed the virus in their feces exposing the rest of the herd.  Often, the only sign of a mild CSF infection in the herd is poor reproductive performance including stillbirths or mummies, piglets born with persistent tremors or malformed organs and piglets born without signs of the disease that become ill months later.


There is currently no treatment for classical swine fever. Any pig suspected of having CSF should be immediately quarantined and examined by the State Veterinarian.


Internet Resources

CSF in the United States 

History: CSF (hog cholera) was first reported in the United States in 1833 at a pig farm in southern Ohio. The disease became endemic to the United States and the country suffered several outbreaks in the late 19th and early 20th centuries. These continued outbreaks of CSF cost pig farmers as much as $50 million per year through the late 1950’s.


The continuing impact of CSF on swine health and the economy led the USDA to initiate a Hog Cholera Eradication Program in 1961.  This eradication program included a ban on classical swine fever vaccines made from live virus (a potential source of new infection), the development of a rapid test to diagnose CSF, and the development of disinfectants that would kill the virus. The eradication program also developed methods to control the spread of the disease including pre-emptive slaughter of animals with government monetary compensation. As a result of this initiative, the United States was declared free of CSF in 1978.


Internet resources:


USDA – Agricultural Research Service


Potential routes of CSF introduction to the US:  The United States remains one of a handful of countries considered free of the disease. However, CSF is endemic to many parts of the world including parts of Mexico, Europe and Asia. Therefore, CSF remains an agrosecurity risk to the US. There are several routes through which CSF may be reintroduced into the United States swine population including:


  1. Smuggling of illegal pork and pork products into the US

  2. Contact with infected wild swine

  3. Consumption of contaminated meat or garbage by swine

  4. Bioterrorism

  5. Contaminated artificial insemination products

  6. Physical transfer from human to pig

Potential Transmission Routes within the US: Although the United States swine herds are considered free of CSF, wild swine can act as a reservoir for the disease. Therefore, it is likely that an outbreak of CSF may occur through contact of our domestic herds with wild swine. In addition, the market for hunting wild swine is large.  In order to supply this market, farmers may smuggle wild swine across state lines further spreading the disease.


CSF surveillance and biosecurity 

In November 2005, APHIS announced the development of an enhanced classical swine fever surveillance program in collaboration with the National Animal Health Laboratory Network (NAHLN). The goals of this surveillance program are to rapidly detect CSF in the US swine population, monitor the risk of introduction of CSF into the swine population and monitor the CSF status of US trading partners. 


Rapid detection of CSF: Rapid detection of CSF in the United States requires testing of certain swine populations.  The swine populations targeted for testing include swine highly suspicious for CSF, swine samples submitted to the animal disease diagnostic laboratories from high risk states, pigs condemned at slaughter and wild pigs.


Swine highly suspicious for CSF: These swine are currently exhibiting the clinical signs of CSF which may include anorexia (unwillingness to eat), huddling, weakness, lethargy, ataxia (incoordination), high fever and constipation followed by diarrhea. Swine with these clinical signs on the farm or at slaughter are to be referred to the State Veterinarian for appropriate CSF testing.


Samples submitted to the animal disease diagnostic laboratory from high risk states: Any sample submitted to the animal disease diagnostic laboratory from a high risk state is eligible for testing through the NAHLN.  States considered high risk for CSF are those that have wild pig populations, garbage feeding operations, backyard swine operations, international air or sea ports and farms that utilize international labor.


Pigs condemned at slaughter: Any pig condemned by a Food Safety and Inspection Service agent at slaughter for having the clinical signs of erysipelas or septicemia, shall be tested for CSF. These diseases have similar clinical signs as CSF.


Wild pigs: Wildlife Services officials will routinely sample wild pigs for signs of CSF.


Monitor risk of introduction of CSF: CSF may be introduced into the US swine population via imported, infected live pigs, artificial insemination products, contaminated garbage used as feed, access to landfills where contaminated meat can be consumed or contact with an infected wild pig. In order to protect the US herds, APHIS will continuously monitor herds that import live pigs or artificial insemination products, pig producers that live on the US-Mexico border, swine producers that feed garbage and herds that employ international workers.


Monitor US trading partners for CSF: Currently, the United States only accepts live swine and pork imports from countries that have been designated free from CSF by the World Organisation of Animal Health (OIE). In addition, if a member nation of the European Union has a CSF outbreak, the US will consider all member nations of the European Union to be involved with the outbreak. As a result, the US will prohibit the import of all pork and pork products from the European Union for 6 months past the containment and eradication of the CSF affected swine.  


Internet Resources:

Biosecurity for Swine Producers


In order to protect the swine herd from becoming infected with an exotic animal disease such as CSF, swine producers are urged to take the following measures:


  • Isolate incoming animals from the rest of the herd and monitor for clinical signs of disease
  • Follow an All In/All Out strategy of pig management and disinfect the facilities between groups
  • Require visitors to wear clean boots and coveralls before coming in contact with the herd
  • Properly clean and disinfect livestock trucks and trailers before entry into the farm
  • Dispose of carcasses promptly and correctly
  • Provide lunch for employees
  • Do not allow employees to have contact with any swine outside the herd
  • Have an effective rodent and insect control program

Internet Resources 


Worldwide CSF outbreaks 

The Netherlands: In January 1997, a farmer in Venhorst, The Netherlands had reported several pigs with anorexia (unwillingness to eat), coughing and blue ears to the local veterinarian. The veterinarian believed the pigs had pneumonia and treated them with antibiotics. When the pigs did not recover, the veterinarian then believed PRRS (porcine respiratory and reproductive syndrome) was the cause of the illness. However, a cadaver brought to the animal disease diagnostic laboratory was diagnosed with CSF on February 4. The significant lag time between finding the first ill pig and diagnosis contributed to the widespread outbreak of the disease and slaughter of millions of animals. 


It is believed that this first outbreak of CSF was introduced into The Netherlands by a livestock truck that had contacted infected pigs in the Paderborn region of Germany. The cold conditions that year preserved the virus and hindered the effective cleaning of the truck. In the weeks following the initial diagnosis of CSF, dozens of outbreaks a week were reported across the country. The CSF outbreak continued until March 1998 with over 700,000 infected pigs destroyed.  In addition, over 1 million pigs were euthanized in pre-emptive slaughter operations and over 7 million pigs were euthanized for animal welfare reasons.  It is estimated that the 1997 CSF outbreak cost The Netherlands $2.3 billion US dollars.

Print Resources:

Elbers AR, Stegeman A, Moser H, et al. The classical swine fever epidemic 1997-1998 in the Netherlands: descriptive epidemiology. Preventive Veterinary Medicine 42 (1999) 157-184

Meuwissen MP, Horst SH, Huirne RB, Dijkhuizen AA. A model to estimate the financial consequences of classical swine fever outbreaks: principles and outcomes. Preventive Veterinary Medicine 42 (1999) 249-270

East Anglia, UK: From June to August 2000, a swine finishing operation in Essex had received several shipments of newly weaned piglets from a breeding farm. The breeding farm had received a routine health inspection by the veterinarian in June 2000. At that time, there weren't any clinical signs of disease present. However, the first sow believed to be infected with CSF was reported as not well on June 20. She died on July 25.

During this time period, the swine herds were battling small outbreaks of post-weaning multi-systemic wasting syndrome (PMWS) and porcine dermatitis and nephropathy syndrome (PDNS). These diseases mimic the clinical signs of CSF. Therefore, it wasn't until August 8, 2000 that CSF was diagnosed at a farm in Suffolk.  Due to the delay, over 16 farms were affected and 74,793 pigs were slaughtered to prevent the further spread of the disease.

It is believed that the use of outdoor enclosures for the breeding herd contributed to the introduction of CSF.  The outdoor enclosures were surrounded by several walking paths that placed the swine in direct contact with the public. It is believed that a hiker on these trails tossed some illegally imported meat into the enclosure with the swine. The meat was contaminated with CSF.

Internet Resources:

DEFRA - CSF Fact Sheet


High Risk States 

  • Arizona
  • California
  • Florida
  • Georgia
  • Hawaii
  • Illinois
  • Iowa
  • Kansas
  • Minnesota
  • Nebraska
  • New Jersey
  • New Mexico
  • New York
  • North Carolina
  • Oklahoma
  • Texas
  • Washington


Last Updated:10/2/2009 12:31 AM

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