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Monograph

Definition

Infectious and contagious disease of the pestivirus genus which induces haemorrhagic septicaemia and various other clinical forms in domestic and wild suidae.

Situation in America

The disease is enzootic in Cuba, Haiti and Dominican Republic with outbreaks reported in the north of Brazil and in the Central States in Mexico. In Central America, outbreaks are reported in Nicaragua, Honduras and Guatemala; Costa Rica and Panama are waiting for the OIE recognition of Free of the disease. In South America, there are reports in Bolivia, Peru, Ecuador, Venezuela and Colombia. Argentina and Chile are recognized as free of the disease.

Susceptible species

Only Suidaes, domestics (swines) and wilds (boars and peccary).
The clinical form of the disease has been described in European boars’ farms. The adult boars are considered as a natural reservoir of the virus in Europe. In America, the role played by these wild animals is unknown on transmission and permanency of the virus in nature. The virus does not affect humans.

Etiological agent

Enveloped, positive RNA virus of the Flaviviridae family, pestivirus genus.

High homology from the antigenic, structural and biological point of view with other pestivirus, notably the "mucosal disease" virus in bovines (BVD/MD) and "border disease" (BDV). Possibility of cross-vaccination: partial immunisation of pigs with the BVD/MD virus.

Only one serotype of the CSFV.
Variable pathogenic potency and tissue tropism according to the strain, and the immunological status of the affected animal or herd.
No similarity with the African swine fever virus.

Inactivated in 48h in the outside environment.
Remains infectious for several months in carcasses and animal products.
Destroyed by 1%NaOh (Sosa) and other commercial disinfectants commonly used for focal disinfection.

Methods of transmission

Sources

Infected suidae in the incubation stage, chronic or asymptomatic infection, immunotolerant persistently infected animals (IPI).

Virulent Matter:

All tissue, secretions and excretions from dead or living infected suidae are virulent: saliva, urine, semen, faeces.
Meat, cured meat and swill are also potential sources of the virus.

Transmission

Direct
• Horizontal: through direct contact with animals (secretions, excretions, semen, blood).
• Vertical: transplacental.

Indirect
• Premises, equipment, clothing, instruments and needles, insemination.
• Ingestion of undercooked pork waste food, swill.

The spreading of the disease from one farm to another is encouraged by animal and human circulation (vertical structure of the porcine sector in certain countries).

Method of contamination

Oronasale, percutaneous (scratches), transplacental, genital.

Symptoms

Incubation period: 2 to 15 days.

The symptoms of both classical swine fever and African swine fever are indistinguishable.

Typical forms

Subacute form: tuberculosis, high fever, the animal dies before developing haemorrhagic signs.

Acute form: fever (40-42°C), lethargy, anorexia, followed by various signs according to the organs affected. The pigs shiver and huddle together.

• cutaneous signs: purple or violet colour (abdomen, ears, groin, legs, tail).
• ocular signs: conjunctivitis
• digestive signs: alternate constipation / diarrhoea, occasional vomiting
• respiratory signs: dyspnoea, coughing, epistaxis
• genital signs: casting, stillbirth.
• nervous signs: ataxia, paresis, trembling, convulsion
• death occurs in 6 to 20 days

The death rate nears the 100% mark in young animals.

Subacute or chronic form: the same symptoms appear but are attenuated. The incubation period is longer and progression is slower and longer than 30 days. Prolonged or intermittent disease periods with anorexia, fever and diarrhoea, cutaneous lesions, retarded growth.

Risk of bacterial proliferation secondary to immunodepression inducing respiratory, digestive or articular complications.

Atypical forms

Death rate is low and the signs discreet.

Congenital form: (piglets)
• Lack of appetite, retarded growth, alternate constipation / diarrhoea, progression towards death in several weeks or months.

Mild form: (sows)
• hyperthermia and capricious appetite,
• foetal death, resorption, mummification
• birth of healthy piglets, asymptomatic carriers, or congenitally affected piglets
• abortion (rare)

Asymptomatic forms

Recovered or Immunotolerant Permanently Infected animals(IPI).

Lesions

Secondary bacterial infections may complicate lesional presentation.

Macroscopic lesions

Acute form:

Haemorrhagic septicaemia type lesions: petechiae and ecchymosis (skin, marble aspect lymph nodes, larynx, bladder, "turkey-egg" kidneys, valvule ileocaecal junction).
Digestive and respiratory tract inflammatory reaction.
Multifocal infarction of the spleen margin.

Chronic form:

Absent or moderate haemorrhagic or inflammatory lesions.
Severe lymphoid tissue depletion: tonsils, lymph nodes, spleen.
Button ulcers in the caecum and large intestine.

Microscopic lesions

Progressive anaemia, intense leucopenia, thrombopaenia.
Lymphoid tissue depletion, reticular hyperplasia of lymph nodes.
Encephalomyelitis with perivascular cuffing.

Diagnosis

Clinical diagnosis

Suspicion on the outbreak of a contagious disease affecting pigs of all ages, inducing severe hyperthermia, diversely associated haemorrhagic cutaneous, ocular, digestive, respiratory and nervous symptoms causing a high death rate.

Differential diagnosis

• African swine fever (it is essential to send samples for laboratory examination)
• Respiratory and reproductive syndrome
• Salmonellosis
• Erysipelas
• Acute pasteurellosis
• Streptococcis
• Poisoning

In the case of an outbreak suggesting swine fever on a farm using the vaccination against the disease, an outbreak of African swine fever should be suspected.

Laboratory diagnosis

Samples:
Blood in EDTA, tonsils, lymph nodes, spleen, kidneys, distal ileum. For atypical forms: runts, carcasses.

Virological diagnosis

• Direct immunofluorescence test on frozen organ cross-sections..
• Virus isolation in cell culture with virus detection by immunofluorescence. Confirmation with monoclonal antibodies.
• RT-PCR or real-time PCR.

Serological diagnosis

Seroneutralisation or ELISA test. Antibodies are detectable at the end of the 2nd or 3rd week of infection and persist throughout the whole of the animal's life.

Treatment

No available treatment.

Prophylaxis

Sanitary prophylaxis

Defensive Sanitary Prophylaxis

In disease-free areas:

• Hygiene: sterilisation of swill (1 hour at 80°C).
• Strict import policy for live pigs and fresh and cured pig meat.
• Quarantine of pigs before admission into the herd.
• Identification and control of animal movements.
• Serological monitoring for breeding sows and boars.

Offensive Sanitary Prophylaxis

In contaminated areas:

• Total, clean, preventive slaughter.
• Disposal of carcasses (incineration or burying).
• Disinfection.
• Control of pig movements.
• Serological monitoring of neighbouring herds.
• Investigation to determine the possible (up-stream) sources and spread of disease.
• Monitoring of the affected area and the surrounding area.

Vaccines

Attenuated virus vaccines: effective as a preventive measure in areas affected by the enzootic but not for total immunity given the difficulty in serological identification of infected and vaccinated pigs.

Faced with these difficulties, disease-free countries or countries beginning to eradicate the disease generally prohibit vaccination.

Vaccines using the Chinese strain or lapinised strain enable serological distinction between the vaccinal strain and the wild strain.

Subunit vaccines have been recently developed. They enable the distinction between vaccinated animals and infected animals and offer an alternative to countries having prohibited vaccination but confronted with recurrent episodes of classical swine fever.

For more information
- Monograph of OIE
- Classical Swine Fever Technical Factsheet (OIE, CSFPH)
- CSFPH website
- USDA-APHIS website