classical swine fever
- Host Animals
- Hosts/Species Affected
- Systems Affected
- Distribution Table
- List of Symptoms/Signs
- Disease Course
- Impact: Economic
- Zoonoses and Food Safety
- Disease Treatment
- Prevention and Control
- Links to Websites
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- classical swine fever
International Common Names
- English: hog cholera; hog cholera infection in utero - exotic; hog cholera, classical swine fever, pestivirus infection in pigs; swine fever
- French: peste porcine classique
Local Common Names
- Germany: klassische schweinepest
OverviewTop of page
Classical swine fever (CSF), also known as hog cholera, is a highly contagious multisystemic viral disease of swine that can run an acute, subacute, chronic, or late-onset course. Swine can also be infected subclinically. Domestic pigs, wild boar and feral pigs are the only animals susceptible to classical swine fever virus (CSFV).
There is a wide range in virulence among CSFV strains. Highly virulent strains cause acute severe disease often resulting in mortality, whereas strains with low virulence give rise to mild disease or subclinical infection. While highly virulent strains were prevalent in the past, most outbreaks are now caused by moderately virulent strains, and the clinical signs are often less severe and distinctive (Spickler, 2015).
The first presumptive outbreaks were reported from the USA in the early nineteenth century, whereas CSF may first have appeared in Europe in the middle of that century. In 1888, the first outbreak was reported in Japan (Fukuhso, 1998) and in South Africa in 1900 (De Kock et al., 1940; Edwards and Sands, 1990). De Schweinetz and Dorset (1903) showed that CSF is caused by a virus. It belongs to the Pestivirus genus, together with bovine viral diarrhoea virus (BVDV) and border disease virus (BDV), within the family of Flaviviridae.
Classical swine fever is on the list of diseases notifiable to the World Organisation for Animal Health (OIE). It is distributed in many countries in Asia, Eastern Europe and South America (Oliveira et al., 2020) and thus hampers international free trade in pigs and pig products. Large areas of Europe, Australasia and North America are normally free of the disease. Outbreaks can cause huge economic damage.
Host AnimalsTop of page
|Animal name||Context||Life stage||System|
|Sus scrofa (pigs)||Domesticated host; Wild host||Pigs|All Stages|
Hosts/Species AffectedTop of page
Pigs and wild boar are the only natural reservoir of CSFV. Pigs and wild boar of all ages are susceptible to CSFV. The virus generally causes higher mortality in piglets than in older pigs, although an increase in mortality with age has been described in fattening pigs (Koenen et al., 1996). Foetuses can also become infected; the outcome depends mainly on the age of the foetus at infection (Oirschot, 1979). Breed-related and other, still unknown, host factors may influence the clinical course of infection (Depner et al., 1996, 1997).
CSFV has been detected in a white-lipped peccary (Tayassu pecari), and experimental infections have been established in common warthogs (Phacochoerus africanus), bush pigs (Potamochoerus larvatus) and collared peccaries (Tayassu tajacu). Experimental infections without clinical signs have been reported in cattle, sheep, goats and deer, but there is no evidence that these species become infected in nature. Strains of CSFV can also be adapted to passage in rabbits (OIE, 2020).
Systems AffectedTop of page
digestive diseases of pigs
multisystemic diseases of pigs
nervous system diseases of pigs
respiratory diseases of pigs
skin and ocular diseases of pigs
urinary tract and renal diseases of pigs
DistributionTop of page
CSF is present in much of Asia, some Caribbean islands, the African countries of Madagascar and Mauritius, and much of South and Central America. The disease has been successfully eradicated from the United States, Canada, New Zealand, Australia and most of western and central Europe. The status of classical swine fever in some areas of Africa may be uncertain due to limited or no surveillance (OIE, 2020).
CSF re-emerged in Japan in 2018, in both domestic pigs and wild boar, after 26 years of CSF-free status (Postel et al., 2019). The involvement of wild boar has made the disease difficult to control (Aoki, 2019; Hayama et al., 2020).
CSF is present in parts of Eastern Europe. The situation concerning CSF in Europe since 2007 is reviewed by Postel et al. (2013). In the EU Member States, only sporadic CSF outbreaks in domestic pigs have occurred since 2009. The reoccurrence of CSF in wild boar in Germany in 2009 shows that the virus can persist at very low levels in local wild boar populations and even intensive surveillance cannot exclude the presence of CSF. The disease remains a continuous threat to the European pig and wild boar populations.
For current information on disease incidence, see OIE's WAHID Interface
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.Last updated: 05 Jan 2022
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|Algeria||Absent, No presence record(s)||Jul-Dec-2019|
|Angola||Absent, No presence record(s)||Jul-Dec-2018|
|Botswana||Absent, No presence record(s)||Jul-Dec-2018|
|Burkina Faso||Absent, No presence record(s)||Jul-Dec-2019|
|Cameroon||Absent, No presence record(s)|
|Central African Republic||Absent, No presence record(s)||Jul-Dec-2019|
|Congo, Democratic Republic of the||Absent||Jul-Dec-2019|
|Djibouti||Absent, No presence record(s)||Jul-Dec-2019|
|Egypt||Absent, No presence record(s)||Jul-Dec-2019|
|Eswatini||Absent, No presence record(s)||Jul-Dec-2019|
|Ethiopia||Absent, No presence record(s)||Jul-Dec-2018|
|Gabon||Absent, No presence record(s)|
|Kenya||Absent, No presence record(s)||Jul-Dec-2019|
|Lesotho||Absent, No presence record(s)||Jan-Jun-2020|
|Libya||Absent, No presence record(s)||Jul-Dec-2019|
|Malawi||Absent, No presence record(s)||Jul-Dec-2018|
|Mali||Absent, No presence record(s)||Jul-Dec-2019|
|Mauritania||Absent, No presence record(s)||Jul-Dec-2018|
|Mayotte||Absent, No presence record(s)||Jul-Dec-2019|
|Mozambique||Absent, No presence record(s)||Jul-Dec-2019|
|Nigeria||Absent, No presence record(s)||Jul-Dec-2019|
|Rwanda||Absent, No presence record(s)||Jul-Dec-2018|
|Saint Helena||Absent, No presence record(s)||Jan-Jun-2019|
|São Tomé and Príncipe||Absent, No presence record(s)|
|Senegal||Absent, No presence record(s)||Jul-Dec-2019|
|Seychelles||Absent, No presence record(s)||Jul-Dec-2018|
|Sudan||Absent, No presence record(s)||Jul-Dec-2019|
|Tanzania||Absent, No presence record(s)||Jul-Dec-2019|
|Togo||Absent, No presence record(s)||Jul-Dec-2019|
|Tunisia||Absent, No presence record(s)||Jul-Dec-2019|
|Zambia||Absent, No presence record(s)||Jul-Dec-2018|
|Zimbabwe||Absent, No presence record(s)||Jul-Dec-2019|
|Afghanistan||Absent, No presence record(s)||Jul-Dec-2019|
|Azerbaijan||Absent, No presence record(s)||Jul-Dec-2019|
|Bahrain||Absent, No presence record(s)||Jul-Dec-2020|
|Bangladesh||Absent, No presence record(s)||Jan-Jun-2020|
|Brunei||Absent, No presence record(s)||Jul-Dec-2019|
|Iran||Absent, No presence record(s)||Jan-Jun-2019|
|Iraq||Absent, No presence record(s)||Jul-Dec-2019|
|Jordan||Absent, No presence record(s)||Jul-Dec-2018|
|Kuwait||Absent, No presence record(s)||Jan-Jun-2019|
|Maldives||Absent, No presence record(s)||Jan-Jun-2019|
|North Korea||Absent, No presence record(s)|
|Oman||Absent, No presence record(s)||Jul-Dec-2019|
|Palestine||Absent, No presence record(s)||Jul-Dec-2019|
|Qatar||Absent, No presence record(s)||Jul-Dec-2019|
|Saudi Arabia||Absent, No presence record(s)||Jan-Jun-2020|
|Turkey||Absent, No presence record(s)||Jul-Dec-2019|
|United Arab Emirates||Absent, No presence record(s)||Jul-Dec-2020|
|Yemen||Absent, No presence record(s)||Jan-Jun-2020|
|Bosnia and Herzegovina||Absent||Jul-Dec-2019|
|Faroe Islands||Absent, No presence record(s)||Jul-Dec-2018|
|Federal Republic of Yugoslavia||Present||1996|
|Union of Soviet Socialist Republics||Present||Original citation: OIE (2000)|
|Isle of Man||Absent, No presence record(s)|
|Jersey||Absent, No presence record(s)|
|Luxembourg||Absent, No presence record(s)|
|San Marino||Absent, No presence record(s)||Jan-Jun-2019|
|Serbia and Montenegro||Present|
|Bahamas||Absent, No presence record(s)||Jul-Dec-2018|
|Bermuda||Absent, No presence record(s)|
|British Virgin Islands||Absent, No presence record(s)|
|Cayman Islands||Absent, No presence record(s)||Jan-Jun-2019|
|Curaçao||Absent, No presence record(s)||Jan-Jun-2019|
|Dominica||Absent, No presence record(s)|
|Greenland||Absent, No presence record(s)||Jul-Dec-2018|
|Jamaica||Absent, No presence record(s)||Jul-Dec-2018|
|Saint Kitts and Nevis||Absent, No presence record(s)|
|Saint Vincent and the Grenadines||Absent, No presence record(s)||Jan-Jun-2019|
|Trinidad and Tobago||Absent||Jan-Jun-2018|
|Cook Islands||Absent, No presence record(s)||Jan-Jun-2019|
|Federated States of Micronesia||Absent, No presence record(s)||Jan-Jun-2019|
|Fiji||Absent, No presence record(s)||Jan-Jun-2019|
|Kiribati||Absent, No presence record(s)||Jan-Jun-2018|
|Marshall Islands||Absent, No presence record(s)||Jan-Jun-2019|
|New Caledonia||Absent, No presence record(s)||Jul-Dec-2019|
|Palau||Absent, No presence record(s)||Jul-Dec-2020|
|Papua New Guinea||Absent, No presence record(s)||Jul-Dec-2018|
|Samoa||Absent, No presence record(s)||Jan-Jun-2019|
|Vanuatu||Absent, No presence record(s)||Jan-Jun-2019|
|Falkland Islands||Absent, No presence record(s)||Jul-Dec-2019|
|French Guiana||Absent, No presence record(s)||Jul-Dec-2019|
|Guyana||Absent, No presence record(s)||Jul-Dec-2018|
|Suriname||Absent, No presence record(s)||Jan-Jun-2019|
PathologyTop of page
The pathology of (sub)acute CSF is that of a septicaemic disease characterized by widespread multiple haemorrhages of various sizes, mainly in lymph nodes and kidneys. Lymph nodes also become oedematous and consequently often have a ‘marbled’ appearance. Histologically, lymph nodes show lymphocytic depletion and reticular hyperplasia. Infarcts are often observed; spleen infarcts are considered to be pathognomonic for acute CSF. (However, these are not considered a consistent field finding.) There is disseminated intravascular coagulation with microthrombi in small blood vessels. Catarrhal, fibrinous and haemorrhagic inflammatory reactions can be seen in the respiratory, digestive, and urogenital tracts. Most pigs with acute CSF show encephalitis with perivascular cuffing. In pigs that die from persistent CSFV infections, the most outstanding lesions are a general exhaustion of the lymphoid system, exemplified by atrophy of the thymus and severe depletion of lymphocytes in tonsil, lymph nodes and spleen. Further consistent findings in persistent CSF cases are degeneration of endothelial cells, button-ulcers in caecum and colon and rib lesions. Foetal infection can result in stillborn piglets having excessive amounts of fluid in body cavities, in limb malformations and defects in the central nervous system, such as cerebellar hypoplasia and hypomyelinogenesis.
DiagnosisTop of page
An outbreak of acute CSF can be tentatively diagnosed in the field on the basis of an anamnesis [the history of a patient and its relatives], and thorough clinical and post-mortem investigations. Clinical signs indicative of acute CSF are described under Disease Course; the most relevant are: high fever, depression, ataxia, and leukopenia. Absence of clinical improvement after antibiotic treatment can be considered a further indication for CSF. In cases of subacute, chronic or late-onset CSF it is much more difficult to make a tentative diagnosis on the basis of clinical signs. The presence of skin lesions and runt pigs is suspect for CSF. At post mortem, haemorrhagic lesions and infarcts throughout the body and severe lymphoid depletion are indicative for CSF.
The following diseases are relevant for differential diagnosis. Acute CSF cannot be reliably differentiated from African swine fever without laboratory tests. Splenomegaly, haematoma-like lymph nodes, oedema of the gall bladder and bile ducts, and lung oedema are more indicative for African swine fever than for CSF. Septicaemic diseases such as salmonellosis, streptococcosis, pasteurellosis, erysipelas, or Haemophilus parasuis infections are of differential diagnostic importance, as is the case for generalized haemorrhages in piglets. The latter lesions can also be caused by thrombocytopenia, or intoxications. Runt pigs can also be observed after malnutrition, enterotoxicosis by Escherichia coli or Clostridium perfringens infections, dysentery or campylobacteriosis. Abortions, mummifications, stillbirth can also be caused by infections with pseudorabies, parvovirus, or porcine reproductive and respiratory syndrome virus. It is very important to differentiate CSF from infections with other pestiviruses. Porcine dermatitis and nephropathy syndrome (PDNS) is another viral disease that closely resembles CSF.
Many countries have an eradication or control programme in progress for CSF, and therefore it is of the utmost importance to rapidly make a definite diagnosis or exclude the disease in case of suspicion. This can only be performed in the laboratory. For this purpose, tonsil, spleen, and kidney samples are collected and submitted, preferably on ice to the laboratory, where frozen tissue sections are prepared. The direct immunofluoresence test (IFT) is used to detect viral antigen (OIE, 1996). The tonsil is the most important tissue for detecting antigen. The results can be available in a few hours. A negative result does not exclude CSF as the cause, and where suspicion remains more samples should be examined. The IFT can yield false-positive results, because pigs can become infected with BVDV [bovine viral diarrhoea virus] and BDV [border disease virus], which share common antigens with CSFV. The differentiation can be made by staining tissue section with conjugated monoclonal antibodies that are directed against conserved epitopes of CSFV, which do not react with BVDV or BDV. In countries where vaccination is applied, it may be necessary to distinguish between vaccine and field virus. This can be performed with selected monoclonal antibodies or in the case of lapinized vaccine strains by their ability to induce fever and antibodies in rabbits. In countries where laboratory facilities are scarce, the diagnosis may be made by inoculating susceptible pigs and vaccinated pigs with tissue homogenates. Presence of CSF in susceptible pigs, and absence in vaccinated pigs indicates CSF.
Isolation of CSFV is usually performed by inoculating a 10% mixed tissue homogenate on PK-15 cells. After 24-72 hours these cell cultures are examined by the direct IFT. The polymerase chain reaction (PCR) is used increasingly often to diagnose CSF (McGoldrick et al., 1999). By using PCR techniques, infected animals can be detected early during the incubation period and for a longer period of time in cases where the pigs recover (OIE, 2020). Enzyme-linked immunosorbent assays (ELISAs) to detect antigen are increasingly applied. However, their sensitivity and specificity could still be improved (Depner et al., 1995). The test is not suitable for the diagnosis of CSF in a single animal, but should only be used at the herd level (OIE, 2020).
Antibodies to CSFV appear between 10 and 21 days after infection and probably persist throughout the animal's lifetime. An CSFV-specific proliferation of T lymphocytes and a cytotoxic T-lymphocyte response have been described in infected pigs (Ishikawa et al., 1995; Pauly et al., 1995). In pigs with chronic CSF, neutralising antibodies can remain absent, be impaired or delayed, or only transiently detectable. Pigs with late-onset CSF do not produce antibodies against the virus.
Virus-neutralisation tests and ELISAs, in various modifications, are commonly used for the detection of antibodies to CSFV. ELISAs are more simple to perform, are rapid and suited for screening a large number of samples, and therefore cheaper. Although some ELISAs use monoclonal antibodies that only recognize CSFV strains and thus should only detect CSFV antibodies, positive results should still be confirmed in neutralisation tests to differentiate between antibodies directed against BVDV or BDV. For this purpose, sera are titrated for neutralising antibodies against CSFV or against BVDV or BDV. Higher antibody titres against CSFV than against BVDV or BDV indicate an CSFV infection (OIE, 1996).
The neutralising peroxidase linked assay (NPLA), fluorescent antibody virus neutralisation (FAVN) and enzyme linked immunosorbent assay (ELISA) may be used for serological diagnosis or surveillance, and are identified by the OIE as fit for purpose for screening for international trade (OIE, 2020).
For more information see the OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals
List of Symptoms/SignsTop of page
|Digestive Signs / Anorexia, loss or decreased appetite, not nursing, off feed||Pigs|All Stages||Diagnosis|
|Digestive Signs / Ascites, fluid abdomen||Pigs|Piglet||Diagnosis|
|Digestive Signs / Bloody stools, faeces, haematochezia||Pigs|All Stages||Diagnosis|
|Digestive Signs / Congestion oral mucous membranes, erythema, redness oral mucosa||Pigs|All Stages||Sign|
|Digestive Signs / Decreased amount of stools, absent faeces, constipation||Sign|
|Digestive Signs / Diarrhoea||Pigs|All Stages||Diagnosis|
|Digestive Signs / Erythema, redness of pharynx||Pigs|All Stages||Sign|
|Digestive Signs / Malformation of jaw, brachygnathia, prognathia||Pigs|All Stages||Sign|
|Digestive Signs / Melena or occult blood in faeces, stools||Sign|
|Digestive Signs / Mucous, mucoid stools, faeces||Sign|
|Digestive Signs / Unusual or foul odor, stools, faeces||Sign|
|Digestive Signs / Vomiting or regurgitation, emesis||Sign|
|General Signs / Ataxia, incoordination, staggering, falling||Pigs|All Stages||Diagnosis|
|General Signs / Back atrophy, wasting||Pigs|All Stages||Diagnosis|
|General Signs / Cyanosis, blue skin or membranes||Pigs|All Stages||Diagnosis|
|General Signs / Dysmetria, hypermetria, hypometria||Sign|
|General Signs / Dysmetria, hypermetria, hypometria||Sign|
|General Signs / Fever, pyrexia, hyperthermia||Pigs|Piglet||Diagnosis|
|General Signs / Forelimb lameness, stiffness, limping fore leg||Sign|
|General Signs / Generalized lameness or stiffness, limping||Sign|
|General Signs / Haemorrhage of any body part or clotting failure, bleeding||Pigs|All Stages||Diagnosis|
|General Signs / Head, face, jaw, tongue atrophy, wasting||Pigs|All Stages||Diagnosis|
|General Signs / Hindlimb lameness, stiffness, limping hind leg||Sign|
|General Signs / Hypothermia, low temperature||Pigs|All Stages||Sign|
|General Signs / Inability to stand, downer, prostration||Pigs|All Stages||Diagnosis|
|General Signs / Kyphosis, arched back||Pigs|All Stages||Diagnosis|
|General Signs / Lack of growth or weight gain, retarded, stunted growth||Pigs|All Stages||Diagnosis|
|General Signs / Lymphadenopathy, swelling, mass or enlarged lymph nodes||Pigs|All Stages||Diagnosis|
|General Signs / Orbital, periorbital, periocular, conjunctival swelling, eyeball mass||Pigs|All Stages||Sign|
|General Signs / Pale mucous membranes or skin, anemia||Pigs|All Stages||Diagnosis|
|General Signs / Paraparesis, weakness, paralysis both hind limbs||Pigs|All Stages||Diagnosis|
|General Signs / Petechiae or ecchymoses, bruises, ecchymosis||Pigs|All Stages||Diagnosis|
|General Signs / Polydipsia, excessive fluid consumption, excessive thirst||Sign|
|General Signs / Reluctant to move, refusal to move||Pigs|All Stages||Diagnosis|
|General Signs / Sudden death, found dead||Pigs|All Stages||Sign|
|General Signs / Swelling, mass external abdomen||Pigs|Piglet||Sign|
|General Signs / Tenesmus, straining, dyschezia||Sign|
|General Signs / Torticollis, twisted neck||Pigs|All Stages||Sign|
|General Signs / Trembling, shivering, fasciculations, chilling||Pigs|Piglet||Diagnosis|
|General Signs / Underweight, poor condition, thin, emaciated, unthriftiness, ill thrift||Pigs|All Stages||Diagnosis|
|General Signs / Weight loss||Pigs|All Stages||Diagnosis|
|Musculoskeletal Signs / Forelimb spasms, myoclonus||Pigs|All Stages||Diagnosis|
|Musculoskeletal Signs / Head, face, neck spasms, myoclonus||Pigs|All Stages||Diagnosis|
|Musculoskeletal Signs / Hindlimb spasms, myoclonus||Pigs|All Stages||Diagnosis|
|Musculoskeletal Signs / Relative shortening forelimb||Pigs|Piglet||Sign|
|Musculoskeletal Signs / Relative shortening hind limb||Pigs|Piglet||Sign|
|Nervous Signs / Circling||Pigs|All Stages||Sign|
|Nervous Signs / Coma, stupor||Pigs|All Stages||Diagnosis|
|Nervous Signs / Constant or increased vocalization||Sign|
|Nervous Signs / Dullness, depression, lethargy, depressed, lethargic, listless||Pigs|All Stages||Diagnosis|
|Nervous Signs / Head tilt||Pigs|All Stages||Sign|
|Nervous Signs / Hypertonia of muscles, myotonia||Pigs|All Stages||Diagnosis|
|Nervous Signs / Seizures or syncope, convulsions, fits, collapse||Sign|
|Nervous Signs / Tremor||Pigs|Piglet||Diagnosis|
|Ophthalmology Signs / Blindness||Sign|
|Ophthalmology Signs / Chemosis, conjunctival, scleral edema, swelling||Pigs|All Stages||Diagnosis|
|Ophthalmology Signs / Conjunctival, scleral, injection, abnormal vasculature||Pigs|All Stages||Diagnosis|
|Ophthalmology Signs / Conjunctival, scleral, redness||Pigs|All Stages||Diagnosis|
|Ophthalmology Signs / Lacrimation, tearing, serous ocular discharge, watery eyes||Pigs|All Stages||Diagnosis|
|Ophthalmology Signs / Purulent discharge from eye||Pigs|All Stages||Diagnosis|
|Pain / Discomfort Signs / Skin pain||Sign|
|Reproductive Signs / Abortion or weak newborns, stillbirth||Pigs|Sow||Diagnosis|
|Reproductive Signs / Lack of libido or erection||Sign|
|Reproductive Signs / Mummy, mummified fetus||Pigs|Sow||Diagnosis|
|Reproductive Signs / Small litter size||Sign|
|Respiratory Signs / Abnormal breath odor, foul odor mouth||Pigs|All Stages||Sign|
|Respiratory Signs / Abnormal breathing sounds of the upper airway, airflow obstruction, stertor, snoring||Sign|
|Respiratory Signs / Coughing, coughs||Pigs|All Stages||Sign|
|Respiratory Signs / Dyspnea, difficult, open mouth breathing, grunt, gasping||Sign|
|Respiratory Signs / Epistaxis, nosebleed, nasal haemorrhage, bleeding||Pigs|All Stages||Sign|
|Respiratory Signs / Increased respiratory rate, polypnea, tachypnea, hyperpnea||Pigs|All Stages||Sign|
|Respiratory Signs / Mucoid nasal discharge, serous, watery||Pigs|All Stages||Sign|
|Respiratory Signs / Purulent nasal discharge||Pigs|All Stages||Sign|
|Skin / Integumentary Signs / Alopecia, thinning, shedding, easily epilated, loss of, hair||Pigs|All Stages||Sign|
|Skin / Integumentary Signs / Cold skin, cool ears, extremities||Pigs|All Stages||Sign|
|Skin / Integumentary Signs / Rough hair coat, dull, standing on end||Sign|
|Skin / Integumentary Signs / Skin erythema, inflammation, redness||Pigs|All Stages||Diagnosis|
|Skin / Integumentary Signs / Skin necrosis, sloughing, gangrene||Pigs|All Stages||Diagnosis|
|Skin / Integumentary Signs / Skin pustules||Pigs|All Stages||Sign|
|Skin / Integumentary Signs / Warm skin, hot, heat||Pigs|All Stages||Sign|
|Urinary Signs / Haematuria, blood in urine||Pigs|All Stages||Diagnosis|
Disease CourseTop of page
Pigs normally become infected via the oronasal route, whereupon CSFV first replicates in the tonsil. Highly virulent strains induce acute CSF. Their spread throughout the body is characterized by a lymphatic, viraemic and visceral phase. The virus initially infects epithelial cells of the tonsil, invades the underlying lymphoreticular tissue, is transferred to regional lymph nodes, wherein it replicates and then gives rise to viraemia. Secondary target organs, such as spleen, lymphoid structures lining the intestine, and bone marrow, produce high amounts of virus leading to a high-titred viraemia. Late in the viraemic phase CSFV infects parenchymatous organs (Ressang, 1973). The virus has an affinity for vascular endothelium and cells of the immune system. A leukopenia and thrombocytopenia develop rapidly after infection and usually persist until death in acute CSF (Weiss et al., 1973). During acute CSF, there is a severe general depression of immune responsiveness (Oirschot et al., 1981). Strains of moderate virulence can induce persistent infections that can be distinguished as chronic or late-onset CSF. The first phase of chronic CSF resembles that of acute CSF, but lasts longer and virus titres are lower in serum and organs. There is a second phase of clinical improvement, wherein there is no or a low-level viraemia, and virus is restricted to epithelial cells of tonsil, ileum, salivary glands and kidney. In this phase there is excessive plasma cell formation, an increase in serum immunoglobulin concentrations and specific antibody production (Cheville and Mengeling, 1969; Mengeling and Packer, 1969). The simultaneous presence of virus and antibody can lead to deposition of antigen-antibody complexes in the kidney, resulting in glomerulonephritis (Cheville et al., 1970). During the third phase of chronic CSF the virus disseminates again throughout the pig, which may be initiated by the immune exhaustion that appears to develop and renders the pigs more susceptible to secondary bacterial infections. Pigs can recover from mild to severe infections with moderately virulent CSFV strains. Such pigs produce neutralising antibodies and a cell-mediated immune response.
Late-onset CSF has an initial period of virtual absence of clinical signs, and is the sequel of foetal infection with strains of low virulence. Pigs have a lifelong high-titred viraemia and viral antigen is widespread throughout epithelial, lymphoidal and reticulo-endothelial tissues. Pigs suffering from late-onset CSF are immunotolerant to the virus. Eventually they develop clinical signs and die (Oirschot and Terpstra, 1977).
The multiplication of CSFV strains with low virulence appears to be restricted to the lymphatic phase: tonsil and regional lymph nodes (Lin et al., 1969). These infections usually run a subclinical course accompanied with a transient leukopenia and followed by a specific immune response. After infection of pregnant sows, the virus infects the foetuses. The outcome of the foetal infection is largely dependent on the age of the foetus and the virulence of the virus.
CSF can range from an acute disease with high mortality to a subclinical infection. After an incubation period of 2-6 days, pigs with acute disease show a high fever, with peaks above 42°C, depression, loss of appetite, ataxia, coughing, conjunctivitis, constipation, diarrhoea, and cyanosis. Most pigs die between 10-20 days post-infection. In subacute CSF, pigs develop similar but less severe signs and succumb within 30 days (Dunne, 1975). Pigs infected with strains of moderate virulence show a great variation in clinical signs (Depner et al., 1996, 1997). They may die from (sub)acute disease, may recover or may survive the acute phase only to succumb later from chronic CSF, or may only suffer from mild disease and subsequently recover. Chronic CSF is characterized by intermittent disease periods with anorexia, fever, diarrhoea, dermatitis and leukopenia, and can result in runt pigs. Such pigs are severely retarded in growth, have skin lesions and stand with arched backs. Pigs with chronic CSF may survive for more than 100 days, but most eventually die. Pigs infected with strains of low virulence usually show only mild disease or remain healthy. A congenital infection can result in abortion, mummification, stillbirth, malformation or birth of weak and trembling piglets. Healthy looking, but infected piglets can be born that develop late-onset CSF, characterized by a long period of freedom from disease, followed by gradually aggravating signs of CSF, including runting. Pigs with late-onset CSF die weeks or months after birth (Oirschot and Terpstra, 1977).
EpidemiologyTop of page
The pig and the wild boar are the sole animals that become infected with CSFV under natural conditions, and thus are the source of virus spread. Pigs usually become infected by the oronasal route and shed virus from saliva, nasal and ocular discharges, urine and faeces, until they die or recover. Pigs with chronic CSF may excrete virus continuously or intermittently. A congenital infection may result in the birth of persistently infected immunotolerant piglets that may shed CSFV for months (Oirschot and Terpstra, 1977).
Direct contact between infectious and susceptible pigs is the most common route of transmission of CSFV. Pigs can become infected at markets and during transport in contaminated vehicles, and thus may introduce virus into a herd. However, the mode of introduction of CSFV into a herd can often not be established (Terpstra, 1987; Elbers et al., 1999).
Sows may become infected by artificial insemination and thus probably by natural mating (De Smit et al., 1999). Aerogenic transmission seems to take place within housing compartments (Laevens et al., 1999). Aerogenic spread between farms may occur in pig-dense regions, where large units with mechanical ventilation are located close together. Transmission of CSFV within and between herds has been estimated by simulation models (Stegeman et al., 1999a, b; Stärk et al., 2000). Man appears to contribute considerably to virus spread within and between herds: for example, through the use of contaminated instruments and medicine bottles. The possibility that insects, dogs, cats and birds act as mechanical vectors of the virus cannot be excluded. Wild boars are an important reservoir of CSFV and they appear to have been the source of many outbreaks (Fritzemeier et al., 1999). Wild boar populations present a constant risk for domestic pigs (Blome et al., 2017).
Pork and pork products are an important indirect source of dissemination, because CSFV can survive in them after processing. When the meat is stored, cooled or frozen, the virus can survive for months. After such products are introduced in a country, and if kitchen leftovers (swill, garbage) are not properly treated before being fed to pigs, they may cause outbreaks (Dunne, 1975; Fritzemeier et al., 1999). Because of this potential danger, some countries prohibit the feeding of swill to pigs.
Advances in molecular epidemiology of CSFV have facilitated the tracing of the source of outbreaks and of transmission routes. The phylogenetic analysis of genome sequences can be exploited to detect or exclude a possible connection between outbreaks (Lowings et al., 1999; Widjojoatmodjo et al., 1999).
The Classical Swine Fever Database (CSF-DB) of the EU and OIE Reference Laboratory for CSF was been implemented as a tool to facilitate exchange of information concerning CSF (Dreier et al. 2007). It offers one of the world’s largest semi-public virus-specific sequence collections combined with a module for phylogenetic analysis. The CSF-DB is a valuable tool for supporting diagnosis and epidemiological investigations and allows for the storage and analysis of traditionally used, well established genomic regions and of larger genomic regions including complete viral genomes (Postel et al., 2016). The CSF-DB is available online at http://viro60.tiho-hannover.de/eg/csf/; access is permitted after a password request.
In 2002, a working group on CSF in wild boar of the Directorate General Health and Consumer Protection (DG SANCO) of the European Commission initiated the establishment of a common database on the epidemiology of classical swine fever in wild boar (see: http://public.csf-wildboar.eu/Default.aspx).
Over the last decades, a decreasing virulence has been observed for the CSFV strains involved in many outbreaks among both wild boar and domestic pigs. In endemically affected countries with official but imperfect vaccination, circulation of less virulent CSFV strains is often masked by partial protection. In combination with management and biosecurity issues (swill feeding, contacts, shared equipment), the virus is maintained over prolonged periods in the domestic pig population (Blome et al., 2017).
Impact: EconomicTop of page
CSF is a re-emerging disease, threatening pork production worldwide (Ganges et al., 2020). CSF can cause enormous economic losses in countries with an intensive pig industry. The losses can be divided into losses for the government, mainly due to the strict stamping out and other control measures that have to be taken, and losses for the entire livestock-production chain, i.e. feed suppliers, breeding organisations, animal traders, slaughterhouses and processing industries (Horst et al., 1999). Severe outbreaks plagued Belgium, Germany, and the Netherlands in the 1990s. In the latter country, the 1997 epidemic resulted in destruction of more than 11 million pigs and estimated financial losses of about 2.3 billion US dollars (Meuwissen et al., 1999). In extensive pig-holding systems in developing countries the animal and economic losses may be less obvious.
Zoonoses and Food SafetyTop of page
CSF is not a zoonosis.
Disease TreatmentTop of page
Treatment for CSF is not available.
Prevention and ControlTop of page
Integral parts of the control measures are timely and reliable diagnosis, stamping out of infected herds, establishment of restriction zones, movement restrictions, and tracing of possible contacts (Blome et al., 2017).
In countries where CSFV is endemic, vaccination is often practiced (but not in the European Union). Only live attenuated vaccines are applied, such as those based on the lapinized Chinese strain, on the cell-culture-adapted Japanese GPE- or on the French PK-15 cell-culture-adapted Thiverval strain. These vaccines are highly efficacious. They induce a rapid (within 4-5 days) and probably lifelong protective immunity, provided the vaccine does not contain too low a virus titre. Vaccination also reduced the replication of virulent CSFV upon challenge and may reduce transmission of CSFV in a vaccinated population (Biront et al., 1987; De Smit, 2000). Because maternal antibodies strongly suppress the generation of active immunity, pigs with maternal immunity should be vaccinated twice. Although the Chinese strain vaccine virus may sometimes spread to contact pigs and foetuses, it has been shown to be highly safe. Vaccination has also been used in cases of emergency to support eradication.
A great disadvantage of vaccination with the above vaccines is that the antibody response after vaccination cannot be distinguished from that after an infection, and as a result it is impossible to convincingly demonstrate absence of wild-type virus in vaccinated populations. To solve this problem, E2 subunit marker vaccines have been developed and shown to be efficacious and safe (Hulst et al., 1993; Moormann et al., 1996; Bouma et al., 1999; De Smit, 2000). Infected herds in vaccinated regions can be detected with an ELISA that detects antibodies against the Erns protein of CSFV (De Smit, 2000).
Controlling endemic infections in wild populations is difficult. Oral vaccination campaigns have been undertaken in wild boar in Germany to reduce the risk of transmission of CSFV to domestic pigs (Kaden et al., 2005; Staubach et al, 2013). It has been proposed that the same bait vaccine used for wild boar could be used for oral vaccination of pigs in backyard production systems, where the systematic implementation of parenteral vaccination proves to be difficult and alternative delivery mechanisms might be needed (Dietze et al., 2013; Milicevic et al., 2013).
In endemic countries, the introduction of CSFV into a herd can best be prevented by purchasing pigs only from free herds and by putting incoming pigs in quarantine. After having been tested negative at the end of a 4-week period they can be admitted. Strict hygiene cannot be emphasized too much as a very important control measure. Thorough cleaning, disinfecting of pens, vehicles and other objects are too often neglected as means to prevent CSF.
Many countries are free of CSF and they take various measures to prevent the introduction of the virus. Usually, they ban the import of live pigs, pork and insufficiently heated pork products from countries where CSF is endemic. In addition, kitchen leftovers from international means of transportation and swill are destroyed or adequately sterilised before being fed to pigs. However, improperly treated pig products are still often the cause of new outbreaks in CSF-free regions. If CSF is diagnosed in 'free' countries, often rigorous measures are taken to eradicate the virus as rapidly as possible. Such eradication programmes are based on notifying suspected cases to the authorities, rapid laboratory diagnosis and immediate destruction of infected herds. In addition, a ban on the movement of pigs in the neighbourhood, intensive surveillance of herds in the endangered area, tracing of the source of infection and of possible contacts is implemented. Sometimes preventive culling of neighbouring herds is performed. At the end of eradication programmes, a serosurvey should demonstrate that a region or country is indeed again free of virus, and contingency plans should enable rapid eradication of CSFV, if the virus should be re-introduced (Crauwels et al., 1999).
In spite of all the above efforts, CSF is still a serious threat for many countries, because of increases in pig density in many areas, the intensification of transport, the wild boar as reservoir for CSFV, the dissemination of CSFV in the food chain and the continuing practice of feeding improperly sterilised swill.
Among the member states of the European Union (EU) a harmonized strategy for diagnosis, control and eradication of CSF is applied (Postel et al., 2013). The EU minimum control measures require depopulation of infected farms, movement restrictions, zoning and surveillance (EU Minimum strategy). Emergency vaccination is authorised for densely populated pig areas although the EU Minimum strategy plus culling in a 1-km ring around infected premises is preferred (Ribbens et al., 2012). Alternative control measures such as antiviral agents, in particular small molecule inhibitors of the CSFV replication, are being explored (Backer et al., 2013; Newcomer and Givens, 2013; Ribbens et al., 2012).
ReferencesTop of page
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