Classical Swine Fever

Definition

Classical swine fever (CSF) is a highly contagious viral disease of pigs. In its acute form the disease generally results in high morbidity and mortality.

History and spread of the disease in Great Britain

CSF was first confirmed in this country in 1864 and was initially allowed to spread unchecked until 1878, when legislation for its control was introduced. The disease persisted for many years until it was finally eradicated from Great Britain in 1966 (see below for details of outbreaks). Since then there have been sporadic outbreaks in 1971 and 1986.

A more serious outbreak in East Anglia in 2000 affected 16 farms. A total of 74,793 pigs including those on contact farms were slaughtered to eradicate the disease. The cause of this most recent outbreak was not finally established but was most likely the result of pigs eating a contaminated imported pork product.

Clinical signs

The symptoms of CSF and African swine fever (ASF) are almost identical and either may occur in chronic or acute form. Laboratory diagnosis is necessary to distinguish CSF from ASF. The incubation period for CSF is variable but is usually between five and ten days. In the acute form pigs develop a high temperature (40.5 degrees C or 105 degrees F), then become dull and go off their food. Other symptoms seen can vary but will include some or all of the following:

• Constipation followed by diarrhoea
• Gummed-up eyes
• Coughing
• Blotchy discolouration of the skin
• Abortion, still births and weak litters
• Weakness of hindquarters.
• Nervous signs including convulsions and tremors in new born piglets.

Differential diagnosis

• African swine fever
• Infection with bovine viral diarrhoea virus
• Salmonellosis
• Erysipelas
• Acute pasteurellosis
• Other viral encephalomyelitis
• Streptococcosis
• Leptospirosis
• Coumarin poisoning
• Porcine Dermatitis and Neopathy Syndrome (PDNS)

How is this disease spread?

The main source of CSF appears to be from pigs eating infected pork or pork products. In this form the CSF virus can remain active for many months.

The movement of infected pigs is a common method of spreading CSF. Apparently healthy pigs may be incubating disease and recovered pigs can excrete the virus for long periods of time.

The virus can exist outside the pig for a long time, so the movement of contaminated vehicles, clothing, footwear and equipment can also spread disease.

Vaccination

Vaccination would not normally be considered as a control measure in the current CSF control strategy. CSF vaccination is restricted by legislation which states that no person shall administer a CSF vaccine to any pig unless authorised to do so by the Secretary of State.

It is possible that vaccination might be used in areas of very high pig density to prevent the occurrence of unrecognised infection in such areas during a prolonged epidemic.

There are currently no operational arrangements in place to mount a widescale CSF emergency vaccination programme in the event of an outbreak in Great Britain.