Rev. sci. tech. Off. int. Epiz., 1999,18 (3), 638-647 Classical swine fever: the European experience and a guide for infected areas J. V a n d e p u t t e & G. Chappuis ( 1 ) (2) (1 ) Merial, 29 avenue Tony Garnier, 69007 Lyons, France (2) Merial, 254 rue Marcel Mérieux, 69007 Lyons, France Submitted for publication: 31 March 1999 Accepted for publication: 28 July 1999 Summary Classical swine fever (CSF) (hog cholera) virus infection is still of world-wide concern, either because of the direct effects of the disease on swine breeding in areas where the virus is epizootic or enzootic, or as a threat in areas where the virus has been eradicated. The authors provide an overview of the characteristics of the disease. Special emphasis is placed on the chronic form of disease, particularly in the late stages of eradication programmes. In the early 1980s, the European Union (EU) was composed of countries which were officially free of the disease (absence of infection and no vaccination) and countries in which vaccination was either permitted or was compulsory. To ensure free trade between the Member States, an eradication plan w a s agreed upon and implemented. Initially, the plan consisted of a combination of vaccination with the Chinese strain of the virus and slaughter and removal of infected herds. Consequently, when the number of infected herds w a s low, vaccination was abandoned and the control of CSF was conducted exclusively by eradication (removal and slaughter). The United Kingdom, Austria, Denmark, Ireland, Luxembourg, Finland and Sweden ceased vaccination before 1980. In the other countries, vaccination was useful in controlling the last epidemics and w a s finally ceased as follows: France in 1983, the Netherlands in 1986, Belgium, Spain and Greece in 1988, Germany in 1989 and Italy in 1990. From 1990 onwards, no vaccination against CSF has been performed in the EU. N e w techniques for the diagnosis of CSF (for example, the enzyme-linked immunosorbent assay based on the detection of the p125 antigen of the virus) have been shown to be of value in the early detection of infected animals. In enzootic areas, the use of vaccines based on the Chinese strain has been successful. Vaccines with at least 100 P D of virus per dose are able to significantly limit the replication of virulent virus in the tonsils. Consequently, shedding of virus after infection can be reduced considerably. In heavily infected areas, vaccination plays a crucial role. The European experience shows that eradication may be achieved when vaccination with highly effective vaccines is combined with effective identification of swine, movement control, early diagnosis and the rapid elimination of infected herds. 50 Keywords Classical swine fever - Diagnosis - European Union - Immunotolerance - Pestiviruses Pigs - Vaccination - Viruses. 639 Rev. sci. tech. Off. int. Epiz, 18 (3) Introduction but harbour and may excrète the virus for several months. Wild boars can also act as a source of CSF infection (4, 11). Classical swine fever (CSF) (hog choiera) remains of major world-wide concern: in disease-free areas, introduction of the disease is a constant threat and in contaminated areas, eradication is the ultimate target. In both cases, the basic characteristics of the CSF virus should be considered whether attempting to maintain or achieve officiai freedom from CSF. The disease is induced by a small enveloped RNA (ribonucleic acid) virus named classical swine fever virus (CSFV), belonging to the Flaviviridae family, genus Pestivirus (36). The virus leads to a systemic disease and provokes a variety of symptoms in pigs. The most common signs in acute cases are high température (> 40°C) and haemorrhages on the ears and abdomen. Thèse symptoms are accompanied by respiratory disease, enteric disease and central nervous disturbances. Symptoms of the chronic form are much less typical, for example, wasting and growth delay, particularly in cases where the other symptoms considered as typical are absent. Différences in strain virulence (9, 23, 34) and the immunological status of the pig affected seem to be the major factors influencing this varying clinical picture. The présence of imrrtunotolerant animais persistently infected with strains of low virulence may complicate early diagnosis of the infection. Thèse animais do not express typical signs and fail to produce antibodies ( 1 3 ) , making serological diagnosis problematic. This situation is similar to immunotolerance exhibited by ruminants infected with the pestiviruses bovine virus diarrhoea virus (BVDV) of cattle and border disease virus (BDV) of sheep (8). Van Oirschot and Terpstra described the case of a carrier sow affected by a field outbreak ( 5 0 ) . The animal gave birth to a litter of 11 piglets. All piglets had CSFV in their pre-colostral plasma. Six piglets were followed until death. At day two after birth, the piglets had high virus titres in the plasma although ail had ingested colostrum with a high antibody titre against CSFV. Finally, all animais developed clinical signs, very late after birth, commonly known as late onset'. Signs such as increasing anorexia and depression, conjunctivitis, dermatitis and locomotion disturbances in varying degrees were noticed and death ultimately occurred at 3 3 2 days after birth. None of the piglets developed antibodies against CSFV. Vannier et al. experimentally reproduced immunotolerant animals from sows infected at 4 3 days of gestation ( 4 8 ) . A similar syndrome was reproduced by Paton and Done in pigs congenitally infected infection with with ruminant-type CSFV may pestiviruses occur after (38). Chronic infection with moderately virulent virus types or with strains which provoke chronic cases of the disease (9, 3 4 ) . The virus may transiently disappear from the sérum before reappearance of clinical disease in a less clearly pronounced form. Such persistently infected animais play an important role in the epidemiology of the disease since the animais are not clearly affected clinically Vaccines are an efficient tool to limit the circulation of the virus in a swine population, on the condition that the vaccines comply with high safety and efficacy requirements and are properly applied. In the early 1980s, some countries in Europe (United Kingdom, Ireland and Denmark) were already completely free of CSF: no vaccination or infection occurred in those countries. However, other countries in Europe were infected (5). This difference in health status of swine in regard to CSF hampered free trade of swine and swine products within the European Union (EU). Free trade of animais and animal products within the EU is only possible if trade does not represent a sanitary risk for countries which are free of disease. As a consequence, sanitary status in regard to CSF had to be harmonised within the EU. Gaining officiai status of freedom from classical swine fever in the European Union The EU commenced a generalised eradication plan in 1980, as detailed and executed according to the Council Directive 80/217/EEC of 22January 1 9 8 0 (14) and Council Directives 80/1095 ( 1 5 ) , 80/1096 ( 1 6 ) , 80/1098 ( 1 7 ) , 80/1099 ( 1 8 ) , 80/1100 (19) and 80/1101 (20) EEC of 11 November 1980. Some important définitions of the Directives are reproduced below: 1. Free of classical swine fever: no classical swine fever has been diagnosed during the last 12 months. 2. Officially free of classical swine fever: no classical swine fever has been diagnosed during the last 12 months, no swine vaccinated against classical swine fever are present and vaccination against classical swine fever has not been authorised for at least 12 months. 3. Region: a country can be divided into well-defined régions which may not all have an identical disease status. This system does not automatically block a whole country for trade if only some of thèse régions are affected by CSF ( 1 7 ) . According to this legislation, all EU Member States were expected to become officially free of CSF five years after having presented an eradication plan. In areas infected with CSF, vaccination was initially intensified in order to cover the entire swine population. The gênerai vaccination programme was accompanied by well-defined measures to be taken in case of suspicion or confirmation of the disease, financial measures for 640 Rev. sci. tech. Off. int. Epiz., 18 (3) compensation, and procedures for identification and tracing of infection. In the case of vaccination, only vaccines that were produced from the Chinese strain and that had at least 100 P D (protective dose 5 0 % ) were allowed (7, 3 0 ) . Vaccination was performed under officiai control. Veterinary Services controlled the vaccinations and assured that all swine in the area concemed were duly vaccinated with the officially-approved vaccines only. In parallel, presence of the disease was controlled through a system of surveillance by veterinarians and Veterinary Services. Every veterinarian had, and still has, the obligation to declare every minor suspicion of disease. After declaration, all movement of personnel, goods and animals, to and from the herd concemed and a defined area around the herd was stopped for a period determined by the veterinary authorities. Cessation of vaccination became possible in countries of the EU as indicated in Table I. 5 0 Cessation of vaccination against classical swine fever in the European Union Twelve months after the last country in the EU ceased vaccination, the EU regarded itself as officially free from CSF. After that date, the legislation according to the Directive EEC/80/217 (14) was applied and in case of problems, special measures were taken by decision of the Commission. Those measures were based on tracing, identification, laboratory analysis and eradication of herds and contact herds. Table I Cessation of vaccination for classical swine fever in the European Union M e m b e r State Date of cessation of vaccination Belgium 1 April 1988 Denmark Before 1980* Germany 1 January 1989 Greece 1 January 1988 Spain 1 July 1988 France 30 April 1983 Ireland Before 1980* Italy 1 January 1990 Luxembourg Before 1980* The Netherlands 15 July 1986 Portugal 1 July 1989 United Kingdom Before 1980* Austria Before 1980* Finland Before 1980* Sweden Before 1980* * Vaccination never applied or ceased before 1980 Source: Commission of the European Union New disease outbreaks were experienced in Belgium in 1 9 9 0 and 1993/1994 (52). These outbreaks were eradicated without vaccination, through an extensive network of epidemio-surveillance, tracing of infection and contacts between herds, laboratory analysis (viral and serological), slaughter of animais in herds and preventive slaughter. The following key topics were at the centre of control and eradication: - effective identification of all animals (43) - movement control of animals and animal products within the EU - agreement and collaboration of transport organisations - efficient logistics for rendering and slaughter of animais (52) - commitment of farmers and their organisations. In the described situation, serological surveillance alone was demonstrated to be insufficient for tracing the infection ( 2 6 ) . This is a further confirmation of the problem posed by chronically infected and immunotolerant pigs. Serological examination must be complemented by virological examination since persistently infected pigs are serologically négative and virologically positive. Furthermore, tracing of secondary outbreaks, clinical investigation of animais and routine laboratory investigation of clinically sick animais for CSF virus or antigens are essential (3). Epidemiological investigation will provide important information about the origin of outbreaks and possible existing risks. Genome analysis of strains together with computer analysis, as described by Greiser-Wilke et al, may be of considérable assistance (22). The financial contribution of the authorities must be stressed: farmers are compensated for ail animais slaughtered within the framework of the eradication programme by the Member States and the EU ( 5 1 ) . Contacts by swine, transport vehicles and humans are the main channels for transmission of CSF. Identification and registration of animais are both essential in order to detect contacts among farms. Tracing forwards and backwards is necessary and probably the most difficult aspect of every eradication attempt. Germany was also confronted with CSF outbreaks in 1 9 9 3 and 1994, simultaneously with Belgium (39). Genome analysis (32, 44) of the isolates provided interesting data regarding the epidemiology. However, genomic différences cannot be related to différent protective patterns among virulent strains and vaccine strains. In 1997, CSF reappeared in the Netherlands, Germany, Belgium, Spain and Italy (1, 2, 3 5 ) . The genomic profile of the isolates and tracing of infected and contact herds through the identification system revealed that all these epidemics were probably linked. Authorities in Belgium were successful in rapidly eradicating the seven infected herds and fifty-five contact herds as a preventive measure. As a consequence, the 641 Rev. sci. tech. Off. int Epiz.. 18 (3) country regained status of officiai freedom from CSF within 4 0 days (35). Eradication was equally successful in Italy. In the EU, the control of CSF remains based on eradication without vaccination. The issue of the use of deleted vaccines, offering the possibility to differentiate between infected and vaccinated animais has been raised. Data currently available for deleted vaccines do not answer the questions of how to detect immunotolerant animais and pigs chronically infected with CSF viruses or whether deleted vaccines offer the same rapid protection in an emergency situation as presently available vaccines (7, 5 3 ) . Furthermore, it is uncertain whether deleted vaccines will offer the same degree of efficacy (> 100 P D per dose of vaccine). The Scientific Veterinary Committee of the EU identified several areas for further investigation, as follows (21): 5 0 - research on safety issues - development of live marker vaccines in order to boost The vaccines currently used are produced either using rabbits (lapinized vaccines) or cell cultures. In both cases the most widely used strain is the Chinese strain. The efficacy and safety of this strain have been proven world-wide (29, 3 0 , 4 0 , 4 5 , 4 9 ) . However, the system of production of the vaccine may significantly influence safety and efficacy. Vaccines produced using rabbits pose the problem of the standardisation of the vaccine viral content. The frequent use of these vaccines in sows has demonstrated that piglets from vaccinated sows may react anaphylactically when vaccinated themselves with lapinised vaccine (6). This problem has been solved by adapting the Chinese strain to cell culture and by elimination of all protein of rabbit origin from the final product. The latter vaccine has been adapted to an ovine continuous dell line. This vaccine has been scrutinised for safety in more than 15,000 swine, including pregnant sows, piglets and fattening swine. Safety of the vaccine has been confirmed by the use of millions of doses (internai Merial data). efficacy - further testing of marker vaccines in the field of control - further research on the companion discriminatory test - further research on vaccination scénarios to be applied in practice - economic cost-benefits - further research on epidemiology of CSF in high density régions. Currently, vaccination has been completely discontinued in countries of the EU. In contrast, the situation in countries in Asia can be compared with that of the EU before 1 9 8 0 . Experience and knowledge from both the EU and Asia should be shared for a better understanding of control measures in the future. Vaccination is still common practice in several countries in Central and Eastem Europe. Vaccination and eradication The situation in Member States of the EU ten to fifteen years ago, demonstrates that controlled vaccination and tracing of movement of pigs are vital steps towards control of the disease. Vaccination was undertaken under following conditions: - high standards of safety and efficacy were maintained (7, 3 0 ) - vaccines contained at least 100 P D per dose of vaccine The vaccine produced on ovine cell line meets the efficacy requirement (minimum 100 P D per dose) and is an interesting tool for controlling the circulation of a virulent virus (7). This vaccine, with an antigenic content of 4 8 0 P D , was able to limit strongly, if not completely, the réplication of virulent challenge virus in the tonsils, when pigs were infected oronasally at one week after vaccination performed in piglets at six weeks old. Long-term immunity using the same vaccine has been successfully demonstrated (41). This type of vaccine has been extremely useful in the eradication of CSF in the EU where vaccination was accompanied by elimination of infected animais and herds. However, in régions or countries where a policy of slaughter of infected animais does not exist, the situation is more complicated, as discussed below. 5 0 5 0 Vaccination in the présence of maternai antibodies In an infected environment, sows may have high antibody titres due to infection with virulent virus. Their offspring may have higher maternai antibodies than offspring of vaccinated non-infected sows. In thèse herds, revaccination of piglets is recommended at the age of nine weeks, or even later in some cases, because of interference of maternai antibodies with vaccination at a younger âge. As stated earlier, persistently infected animais pose an important risk and are difficult to detect. In a vaccinated environment, thèse animais should be found and eliminated. - vaccines were administered under officiai control. Persistently infected animais: response to vaccination In an infected environment, vaccines are the basic tools for control and eradication. Vaccines can drastically reduce the circulation of virulent virus and prohibit or significantly minimise the économie losses due to CSF, on the condition that the vaccines used meet the highest standards of safety and efficacy and that administration is correctly performed. Immunotolerant animais are unlikely to respond to vaccination (33). Animais that have been chronically infected with CSF do not always demonstrate a clear antibody response following a CSF infection. It is not known how thèse animais react to vaccination, however, chronically infected pigs shed CSF virus. 5 0 Rev. sci. tech. Off. int. Epiz., 18 (3] 642 The usefulness of precolostral vaccination Although technically proven, the practicability of precolostral vaccination is an important obstacle (28, 2 9 ) . définitive resuit is provided. The number of samples that can be examined is limited. Spleen, ileum, mesenteric lymph node, blood, parotis and tonsil are the most appropriate material for the detection of virulent and less virulent strains. Virus may be isolated from Diagnosis these tissues only two days after exposure. Kidney is also frequently used for this purpose. Other organs such as skin, tongue, brain and tonsil are recommended by Pan et al. ( 3 7 ) . The clinical signs that are typical of CSF consist of petechiae on the skin, reddening of ear tops, anorexia and fever, accompanied by central nervous disturbances and diarrhoea. The incubation period of CSFV is approximately six days. Early signs, such as anorexia and fever, appear from the second day after infection. The symptoms of CSF may be confused with salmonellosis, actinobacillosis, erysipelas, African swine fever, porcine reproductive and respiratory syndrome and other diseases. In utero infections may give rise to abordons, stillbirths and foetal anomalies. Typical anatomo-pathological lesions are necrotic tonsils, congested, swollen and haemorrhagic lymph nodes, necrosis of the ileocaecal valve and petechial haemorrhages in organs such as the epiglottis, larynx, rénal cortex, urine bladder and small intestine. In cases of congenitally persistent infection and chronic CSF, typical clinical signs as described above may be completely or partially absent. Symptoms are commonly limited to fever, anorexia and poor performance. Concurrent infections occur fairly frequently, which further complicates establishment of a clinical and pathological diagnosis of CSF. The difference in clinical signs and pathology between typically virulent strains and the more chronic type of strains has been described by Kamolsiriprichaiporn et al. (23, 2 4 ) . Given the various difficulties in establishing a reliable clinical and anatomo-pathological diagnosis, laboratory diagnosis is an essential tool in control of the disease. As mentioned before, persistently infected animals appear healthy for some time, although these animais are continuously infecting the environment. Identification of persistently infected animais is an important part of ail control measures. The quality of the antiserum used as conjugate may influence the results. Monoclonal antibodies are recommended for immunofluorescence. However, virus is likely to be less easily isolated from these tissues in the case of less virulent strains (24). Irrespective of the type of tissue taken, viruses of low virulence yield less virus per sample than virulent viruses, so that the risk of false negative results is real. Nevertheless, virus isolation remains the most reliable, 'gold standard' and the most useful method to test single animals. The number of samples that can be examined may be increased by the use of less labour-intensive enzyme-linked immunosorbent assay (ELISA). The use of thèse kinds of tests is based on knowledge of the molecular structure of CSF virus. From a molecular point of view, ruminant pestiviruses and CSFV are very closely related: three major structural glycoproteins, gp44/48(E ), g p 3 3 ( E ) and g p 5 5 ( E ) have rns x 2 been determined in CSFV (42). Thèse are very similar to analogous glycoproteins determined in ruminant pestiviruses. Ail pestiviruses share a non-structural protein, p 125/80 (now commonly called NS2-3), which represents the most conserved protein within the genus (12). Identical epitopes are present on p l 2 5 and p80 (NS-3) and monoclonal antibodies have been produced that react uniformly with thèse two non-structural proteins (12). Non-cytopathic pestiviruses only express the non-structural protein ( p l 2 5 ) (36). Most, if not all, CSF strains are non-cytopathic and only express the non-structural protein p l 2 5 . Thèse non-structural proteins are of major importance as diagnostic tools for pestiviruses in gênerai and CSF in particular (10, 25, 4 6 ) . Until now, a clear distinction among Laboratory diagnosis starts with the collection of appropriate material. The most frequently applied methods are the fluorescent antibody test on organ sections and virus isolation in cell culture. Samples should be as fresh as possible and submitted rapidly to the laboratory. Indeed, if samples are not fresh, cell destruction may render immunofluorescence on organ culture difficult or even impossible to perform. If samples for virus isolation cannot be treated immediately, they should be frozen immediately after collection. These techniques are cumbersome and need specialised equipment, skilled personnel and adapted infrastructure. Multiple passages are frequently necessary (up to three, one per week) before virus isolation is positive, causing a long delay before a pestiviruses as serological groups has not been possible. Distinctions can only be made with monoclonal antibodies against different epitopes of these structural proteins ( 2 7 ) . Extensive pathogenesis studies determined the key role of persistently infected animais in pestiviruses in cattle (8). The détection and élimination of persistently infected animais, followed by vaccination are the main tools for control of pestiviruses in ruminants. Non-cytopathic virus types typically replicate in cell cultures without showing cytopathic effect, therefore complicating détection. Persistent infection results from infection during early pregnancy; when infection takes place during the first third of pregnancy, the infecting 643 Rev. sci. tech. Off. int. Epiz., 18 (3) antigen is not recognised as a foreign antigen but as a self-antigen ( 4 7 ) , thus, no antibodies are developed against the antigen. The diagnosis of persistently infected, and in particular, immunotolerant animals can only be achieved by virus isolation or by detection of the p l 2 5 antigen which is produced during virus replication. the only eradication policy that can be applied is the one based on an effective organisation of reliable and rapid diagnosis, prompt declaration of the disease outbreak, identification of animals and farms and eradication. This policy is applied in North America, the EU, Australia and New Zealand. However, in many of these countries vaccination was an essential part of the control policy prior to obtaining this The p 1 2 5 antigen detection kit was used by Koenen and Lefebvre in pigs ( 2 5 ) . Results of a contact challenge experiment are reported where pigs of different ages were placed in different degrees of contact with one pig intramuscularly or intranasally infected with a moderately virulent strain of CSF. The clinical symptoms of the pigs in direct contact were more pronounced than pigs in non-direct contact. Older pigs did not always exhibit clear symptoms of CSF although the presence of virus could be directly confirmed by virus isolation as well as indirectly confirmed by p l 2 5 antigen detection with an ELISA antigen capture test. Similar results have been described by Lipowski et al. (31) using a p i 2 5 detection test on blood, leukocytes and organs. These trials indicate the interest of using the p l 2 5 antigen capture test. The test is less time-consuming than virus isolation, easier to perform and particularly indicated for screening large numbers of animals. In adult animals, viraemia can be short-lived, therefore sampling of sick animals and/or animals with fever is highly recommended. In a vaccinated environment, the p l 2 5 test may be of particular interest since negative results are obtained for CSF vaccine produced on an ovine continuous cell line (7), similar to the results obtained using immunofluorescence at one week after vaccination (conjugate supplied by the National Veterinary Institute in Brussels). high sanitary status. W h e n the number of cases is high, the price of an eradication policy without vaccination is prohibitive. In highly infected areas, vaccination should be used as the pivotal part of the control plan, accompanied by an extensive and effective diagnostic network. Pigs persistently infected with CSFV do not always display clear clinical signs, seroconversion may be absent and high amounts of virus may be shed over long periods of time. Since these animals may remain seronegative over long periods, if not for life, a control based on serological diagnosis alone is questionable. These virus carriers need to be detected and eliminated. Clinically sick animals should be tested for CSFV. New diagnostic techniques based on ELISA, for the detection of CSF antigen in blood and organs, open up possibilities of testing a high number of samples in a relatively short time. This should increase knowledge regarding the infection situation at a herd and regional level. Furthermore, this testing could enable the elimination of infected herds to begin while maintaining vaccination. Vaccines must be sufficiently potent to reduce the circulation of virus to the greatest possible extent. Their safety level must be such that in the case of an emergency, vaccine can be The p l 2 5 tests detect swine and ruminant pestivirus antigens which is an advantage in an eradication administrated to all animals in a herd in a short period of time. programme. Ruminant and swine pestiviruses are very closely related and The combined application of high quality vaccines and the ruminant pestiviruses can provoke signs very similar to detection and elimination of chronically or persistently chronic forms of CSF, particularly in sows infected early infected animals are crucial for the success of CSF control during pregnancy ( 3 8 ) . In trying to differentiate between programmes. ruminant and swine pestiviruses, extremely precious time may be lost for the implementation of the appropriate control measures. Conclusions The method of control of CSF will primarily depend on the disease situation and legislation in the country concerned. In areas where the disease frequency and/or pig density is low, Rev. sci. tech. Off. int. Epiz., 18 (3) 644 Peste porcine classique : l'expérience européenne et un guide pour les régions infectées J. Vandeputte & G. Chappuis Résumé La peste porcine classique reste un problème mondial, du fait de ses conséquences directes sur la production porcine lorsque la maladie est enzootique ou épizootique et du fait de la menace qu'elle représente lorsque la maladie a déjà été éradiquée. Les auteurs rappellent les caractéristiques de cette maladie. Une attention particulière est portée à sa forme chronique, parce qu'elle semble poser des problèmes notamment durant les stades finaux des programmes d'éradication. Au début des années 1980, les États membres de l'Union européenne (UE) se répartissaient en deux groupes : ceux qui ne pratiquaient plus la vaccination et qui étaient en même temps indemnes d'infection (c'est-à-dire officiellement indemnes de la maladie) et ceux où la vaccination était soit autorisée soit obligatoire. Afin de permettre le libre échange entre les différents États membres, un plan d'éradication fut mis au point au niveau de l'UE. Initialement, le plan combinait la vaccination avec la souche chinoise du virus et l'éradication (abattage sanitaire). Dès que le taux d'infection était tombé à un niveau suffisamment bas, la vaccination était abandonnée et le contrôle de la maladie visait uniquement à l'éradication (par abattage sanitaire). Le Royaume-Uni, l'Autriche, le Danemark, l'Irlande, le Luxembourg, la Finlande et la Suède avaient déjà arrêté la vaccination avant 1980. Dans les autres pays, la vaccination a permis de contrôler les dernières épidémies avant d'être finalement abandonnée : en France en 1983, aux Pays-Bas en 1986, en Belgique, en Espagne et en Grèce en 1988, en Allemagne en 1989 et en Italie en 1990. Depuis, aucune vaccination contre la peste porcine classique n'a été pratiquée dans l'UE. De nouvelles techniques de diagnostic, par exemple l'épreuve immunoenzymatique pour la détection de l'antigène p125 du virus, ont prouvé leur utilité dans la détection précoce d'animaux infectés. Pour les zones enzootiques, la vaccination avec la souche chinoise semble extrêmement efficace. Des vaccins contenant au minimum 100 P D de virus par dose sont capables de limiter de façon significative la réplication du virus sauvage au niveau des amygdales, ce qui réduit considérablement la diffusion du virus dans l'environnement. Dans les régions très infectées, la vaccination joue un rôle crucial. L'expérience européenne montre qu'il est possible d'éradiquer la maladie si l'emploi de vaccins d'une grande efficacité est accompagné d'une bonne identification des porcs qui permette le contrôle des mouvements des animaux, d'un système de diagnostic précoce et d'une élimination rapide des troupeaux infectés. 50 Mots-clés Diagnostic - Immunotolérance - Peste porcine classique - Pestivirus - Porcs - Union européenne - Vaccination - Virus. 645 Rev. sci. tech. Off. int. Epiz., 18 (3] Peste porcine clásice: experiencia europea y guía para zonas infectadas J. Vandeputte & G. Chappuis Resumen La peste porcina clásica sigue constituyendo un problema en todo el mundo, tanto por sus repercusiones directas sobre la producción porcina, en zonas donde la enfermedad es epidémica o enzoótica, como por la amenaza que supone en zonas donde ya ha sido erradicada. Los autores repasan las características generales de la enfermedad,, haciendo hincapié en su forma crónica, que plantea problemas sobre todo en las etapas finales de los programas de erradicación. A principios de los años 1980, los Estados Miembros de la Unión Europea (UE) se repartían en dos grupos: países donde no se practicaban vacunaciones y que estaban libres de infección (esto es, países oficialmente libres de la enfermedad); y países donde se permitía u obligaba a vacunar a los animales. Con el fin de hacer posible el libre comercio entre todos los países de la UE, se implemento un plan de erradicación. En su primera fase, el plan combinaba campañas de vacunación (con la cepa china del virus) con campañas de erradicación (sacrificio sanitario de los rebaños infectados). Posteriormente, cuando la tasa de rebaños infectados cayó a un nivel lo bastante bajo, se abandonaron las vacunaciones para fiar la lucha contra la peste porcina clásica exclusivamente a la erradicación (sacrificio sanitario). El Reino Unido, Austria, Dinamarca, Irlanda, Luxemburgo, Finlandia y Suecia ya habían interrumpido las vacunaciones antes de 1980. Los demás países continuaron con sus campañas a fin de controlar los últimos brotes epidémicos, y después fueron interrumpiéndolas progresivamente en el orden siguiente: Francia en 1983, Países Bajos en 1986, Bélgica, España y Grecia en 1988, Alemania en 1989 e Italia en 1990. A partir de 1990 no se han realizado vacunaciones contra la peste porcina clásica en el seno de la UE. Nuevas técnicas de diagnóstico de la peste porcina clásica, como el ensayo inmunoenzimático para la detección del antígeno p125 del virus, han demostrado ser de gran utilidad para la detección precoz de animales infectados. En zonas donde la enfermedad es endémica, el uso de vacunas con la cepa china parece sumamente eficaz. Las vacunas con un mínimo de 100 P D de virus por dosis son capaces de contener de forma significativa la replicación del virus virulento en las amígdalas, lo que reduce considerablemente la excreción de virus y su difusión en el entorno. En zonas con elevada tasa de infección, las vacunaciones desempeñan un papel crucial. La experiencia europea demuestra que es posible erradicar la enfermedad combinando el uso de vacunas de gran eficacia con una identificación eficiente de los animales que permita controlar sus desplazamientos, establecer un sistema de diagnóstico precoz y eliminar con rapidez los rebaños infectados. 5 0 Palabras clave Diagnôstico - Inmunotolerancia - Peste porcina clâsica - Pestivirus - Porcinos - Union Europea - Vacunaciôn - Virus. • Rev. sci. tech. Off. int. Epiz., 18 (3) 646 References 1. 2. European Economic Swine Fever Laboratories, 1 6 - 1 7 J u n e , Vienna. 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