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classical swine fever (CSF) facts

peste clasica, swine fever, varkenspest, peste porcine, Schweinepest, hog cholera

 

CSF Virus   Clinical signs   Diagnosis   Differential diagnosis

Autopsy findings   Reproductive effects   Occurrence   Spread   Literature

OIE: Diagnosis Spread Survival of classical swine fever virus: factsheet

 

 
 

CSF in United Kingdom: control & past outbreaks   CSF in Wild Boar in Europe: EU

 

About CSF Virus

CSF is caused by infection with CSF (hog cholera) virus, which is a member of the Pestivirus  genus of the Flaviviridae  family of RNA viruses. Classical swine fever virus was formerly classified in the Togaviridae  along with flaviviruses.

Clinical signs

Clinical signs usually appear 5-10 days after infection (occasionally longer). An individual pig may show one of four types of clinical effect:

a) Peracute (sudden death)
Especially at the beginning of a farm outbreak, young pigs may be found dead without any prior sign of illness;
 

b) Acute CSF (most common form)
Fever (40.5-41.5 °C,105-107°F) is often the first sign, then depression, weakness, anorexia, conjunctivitis. Constipation may be followed by diarrhoea or vomiting. There may be purple discoloration of abdominal skin, or necrosis of the tips of extremities (ears, tail, vulva). Neurological signs may occur: incoordination, tremors, convulsions, circling.
There is a high mortality (close to 100%) of acutely affected pigs, usually within a week of initial signs.
Other infections may occur concomitantly with CSF, the classic example being Salmonella choleraesuis

c) Chronic CSF
This form of disease occurs particularly with some low virulence strains of virus or when CSF strikes in vaccinated herds.
Weight loss, hair loss, dermatitis, discoloration of abdomen or ears. Affected pigs may recover or relapse.
 

d) Subclinical CSF
Occurs particularly in pigs infected before birth, or in pigs which have been vaccinated.
No signs are seen, but they may be infectious to other pigs.

Reproductive effects

There may be abortions, stillbirths, mummifications and also congenital tremor of piglets.

Autopsy findings

Peracute cases may show no gross lesions. In acute cases there are haemorrhagic lesions at autopsy. The haemorrhages are most marked under the kidney capsule and in lymph nodes, ileocaecal valve, bladder and larynx. There may also be skin reddening.

haemorrhagic swollen lymph node - medial retropharyngeal
(courtesy of Dr. Stan Done, Veterinary Laboratories Agency UK)

Intestinal "button ulcers" may be seen, particularly in the proximal colon. They are 1-2 cm diameter with a necrotic centre.

button ulcers - internal surface of colon
(photo courtesy of L.D.Sims)

Cerebellar hypoplasia occurs in neonatal pigs with congenital trembling.

Spread (epidemiology)

Pig is the only species clinically affected although the virus can replicate transiently in sheep and cattle. Wild boars can be a reservoir.

Pigs can become infected by ingestion, inhalation, genital (natural or A.I. semen) infection, by contamination of abrasions or by transplacental infection of fetuses.

Most spread of CSF is by movement of infected pigs or feeding of inadequately cooked garbage (swill). Spread by artificial insemination was first recognised during the Netherlands epidemic of 1997.

Persistent carriers of CSF virus can result from the phenomenon of immunotolerance to CSF virus. Immunotolerance can arise from transplacental infection during fetal life and results in a lifelong high level of viraemia (virus in the blood) without any antibody response. These pigs can only be detected by virus isolation, or by immunohistochemistry after death. Further information can be found in the Chapter on CSF in "Diseases of Swine", 8th EDITION, 1999 (Details of the book and how to order on-line).

Local spread from infected farms to neighbouring farms within 1 km is well recognised, although the precise means of transmission can rarely be proven. Birds, rodents, pets or other animals may be involved. Slurry spreading is also possibly involved.

Spread can be associated with vehicles used for moving live pigs or for disposing of carcasses or manure. Other vehicles are theoretically possible but not proven e.g.feed delivery vehicles.

Spread by fomites (e.g. human clothing, footwear or injection needles) or by biting insects is also possible.

Spread in the UK epidemic 2000

Pig movements have been significant in the UK outbreaks, particularly in the early outbreaks. Local spread (particularly to pigs within 1 km of infected farms) has also been important

East Anglia has a large population of birds, deer, dogs and foxes which might be mechanically spreading the CSF virus. This is also a time of year for spreading pig manure on the land. "Local spread" (to farms within 1 km) was a significant factor in the huge Dutch CSF epidemic of 1997-8. Attempts to spread the virus experimentally via rats have been unsuccessful.

Occurrence

Outbreaks have occurred widely in the world. The disease is enzootic in some European countries, South America and the Far East.

In the European Union (EU) CSF is enzootic in the wild boar populations of Germany & Italy (Sardinia).

In the year 2000 there have been outbreaks in Bulgaria and Thailand. Most of us assume that virus is enzootic in China. In 1999 there were outbreaks reported in Argentina, Croatia, Germany, Italy and Luxembourg.

The island of Sardinia had 17 outbreaks of classical swine fever in 1998 and 6 in 1999. African swine fever is also enzootic (endemic) in Sardinia. In March 1999 four CSF outbreaks occurred in the regions of Piedmont and Emilia-Romagna in Italy.

CSF was eradicated from Britain in 1966, although there have subsequently been limited outbreaks in 1971, 1986 and 1987 as a result of infected meat being fed in swill.

Eradicated from the USA in 1978 after a 16 year programme.

Diagnosis

In herds with suspicious clinical symptoms, diagnosis can be confirmed by:

Negative results take longer to confirm (about 4 days) than positive ones. A negative result for a suspect herd also runs into thr problem of how many pigs should be sampled and for how long.

The tissues of choice for virus detection are the tonsils, but mandibular, maxillary and mesenteric lymph nodes and any other organs showing lesions can be useful.

In the UK epidemic, diagnostic tests commonly used for confirming diagnoses are RT-PCR (polymerase chain reaction), fluorescent antibody test & virus isolation

Immunotolerance to CSF is a recognised phenomenon. Infection during fetal life results in a lifelong high level of viraemia without any antibody response. These pigs are a dangerous source of infection and can only be detected by virus isolation, or immunohistochemistry after death.

Differential diagnosis

In 1996, eight suspected cases of CSF were reported to the U.K. Veterinary Laboratories Agency. Five of these followed autopsies undertaken at regional Veterinary Investigation Laboratories. Two cases were subsequently diagnosed as thrombocytopenic purpura, the most common differential diagnosis for swine fever. Amongst the others were individual cases of erysipelas, Pasteurella  infection and colisepticaemia.
The other three reported suspect cases were all negative for swine fever.

In 1995, 10 suspected cases of CSF were reported to the U.K. Veterinary Laboratories Agency. All were negative. In young pigs the commonest differential disease is Purpura haemorrhagica. Similar autopsy findings in older pigs are usually due to blocking of capillaries by immune complexes, mostly involving Erysipelothrix. The classic sources of mistaken CSF diagnoses in the 1950s and 1960s were Streptococcal septicaemia and Salmonella choleraesuis infection. These are only occasionally seen nowadays in the U.K.

Border disease virus occasionally infects pigs. In this past this closely related pestivirus has resulted in false positive antibody tests for classical swine fever

Reference: Lund, L.J., (1996), The Pig Journal, Vol. 37, p.55.

A new swine disease which closely resembles CSF is porcine dermatitis and nephropathy syndrome (PDNS). Many cases of PDNS are being reported as suspected swine fever outbreaks.

 

NEW books
on
Diseases of Pigs
detailed reviews of CSF & ASF

 

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