Laboratory experience during the classical swine fever virus epizootic in the Netherlands in 1997-1998

Classical Swine Fever-An Updated Review

Classical swine fever (CSF) remains one of the most important transboundary viral diseases of swine worldwide. The causative agent is CSF virus, a small, enveloped RNA virus of the genus Pestivirus. Based on partial sequences, three genotypes can be distinguished that do not, however, directly correlate with virulence. Depending on both virus and host factors, a wide range of clinical syndromes can be observed and thus, laboratory confirmation is mandatory. To this means, both direct and indirect methods are utilized with an increasing degree of commercialization. Both infections in domestic pigs and wild boar are of great relevance; and wild boars are a reservoir host transmitting the virus sporadically also to pig farms. Control strategies for epidemic outbreaks in free countries are mainly based on classical intervention measures; i.e., quarantine and strict culling of affected herds. In these countries, vaccination is only an emergency option. However, live vaccines are used for controlling the disease in endemically infected regions in Asia, Eastern Europe, the Americas, and some African countries. Here, we will provide a concise, updated review on virus properties, clinical signs and pathology, epidemiology, pathogenesis and immune responses, diagnosis and vaccination possibilities.

Diagnostic methods for detection of Classical swine fever virus—Status quo and new developments

Classical swine fever (CSF) is a highly contagious disease causing major losses in pig populations almost worldwide. The disease occurs in many regions of Asia, Central and South America and parts of Europe and Africa. Some countries have eradicated the disease (Australia, USA, Canada, within the EU), yet it keeps recurring sporadically (South Africa, Germany, Netherlands, England). The causative virus is a member of the genus Pestivirus, family Flaviviridae. The first diagnosis of CSF is based on the recognition of clinical signs by the veterinarian in the field and by post mortem findings. Many signs are not exclusively associated with CSF and they may vary with the strain of virus, age and health status of the pigs. Since clinical signs may be confused with other pig diseases, laboratory diagnosis of CSF is indispensable. Both the Office International des Epizooties (OIE) and the European Union, have approved diagnostic manuals establishing sampling methods and diagnostic procedures for the confirmation of the disease. In this review, experiences with current tests will be analyzed and complemented with new developments, with emphasis on the polymerase chain reaction after reverse transcription of the RNA genome (RT-PCR).

Classical swine fever--an update

Classical swine fever (CSF) is a serious and contagious viral disease of pigs and wild boar with a widespread worldwide distribution. The immunopathology of the disease is poorly understood, but the ability of the CSF virus to infect cells without triggering apoptosis and to kill uninfected cells is probably highly significant. The virus may be spread by various direct and indirect methods, but in most cases the exact mechanisms involved in local spread between farms are not known. Excellent diagnostic tools and typing methods are available, but tests that could be performed on-farm, in pre-clinically infected pigs or on meat would also be advantageous. A more complete picture of the viruses circulating in different parts of the world is needed. There is great interest to develop and use marker vaccines for the control of CSF in domestic pigs and in wild boar. Epidemiological modelling is increasingly used to evaluate control options.

Swine fever: classical swine fever and African swine fever

Because of the clinical and pathologic similarity to common endemic diseases, introduction of CSFV or ASFV strains of moderate to low virulence represents the greatest risk to North American swine herds. Producers, veterinarians, and diagnosticians should increase their awareness of these devastating diseases and request specific diagnostic testing whenever they are suspected. Production practices that improve biosecurity will reduce the risk of introduction of CSF and ASF and limit the spread if an incursion occurs. Additional resources. The following Web sites contain excellent color photographs that will assist producers and practitioners in identifying clinical signs and gross lesions associated with CSFV and ASFV: http://www.vet.uga.edu/vpp/gray_book/FAD and http://www.pighealth.com. The latter Web site and the OIE Web site (http://www.oie.int) offer updated information on current worldwide epizootics of ASF and CSF and other swine diseases. Details of biosecurity procedures can be found at http://www.agebb.missouri.edu; see publication G2340.

Laboratory diagnosis, epizootiology, and efficacy of marker vaccines in classical swine fever: a review

Detection of classical swine fever virus (CSFV) can be achieved by a range of assays of which the most commonly used are: immunohistochemical and virus culture techniques. New developments have enabled the detection of viral proteins by enzyme-linked immunosorbent assays (ELISAs) and the detection of the viral genome by RT- PCR. So far, laboratory findings show that the latter assays may supplement or replace the conventional techniques in the near future. The detection of serum antibody against structural and non-structural proteins of CSFV has been improved by developments in recombinant DNA techniques and has lead to a range of ELISAs. Although the characteristics of these ELISAs are excellent, positive results still need to be confirmed in the virus neutralization test. The available amount of sequence data enables diagnosticians to type strains of CSFV as different by comparing several parts of the genome. In some cases, this can provide conclusive evidence if a primary or secondary outbreak has been detected. Increased efforts focused on the retrieval of relevant data on the introduction of CSFV in a pig holding and the spread of CSFV in- and between pig holding(s) has generated more insight into the epizootiology of the disease. A successful control and eradication programme for classical swine fever (CSF) can consist of zoosanitary measures and/or vaccination. The latter can compromise the export of live pigs and pig products considerably unless marker vaccines have been used. Several studies were performed to determine the efficacy of an E2 subunit vaccine and live recombinant vaccine candidates. Firstly, we determined the 95% protective dose of an E2 subunit vaccine at 32 microg E2 per dosage after a single application. Further studies with a single administration of the subunit vaccine showed that: the vaccine was stable for a prolonged period after production, was able to reduce horizontal and vertical transmission of CSFV among vaccinated pigs, and provided protection for at least 6 months. An E(rns) antibody discriminatory assay was developed for use in combination with the subunit vaccine. Evaluation of the E(rns) ELISA showed that the sensitivity of the assay was lower than but that the specificity was equal to that of existing antibody assays. Two live recombinant marker vaccines were evaluated for the induction of clinical protection and reduction of transmission of CSFV shortly after vaccination. Results showed that these vaccines provided good clinical protection 1 week after a single vaccination. Research has shown that marker vaccines can be used in the future to support the control and eradication of CSFV.

Introduction to classical swine fever: virus, disease and control policy

Classical swine fever virus is a spherical enveloped particle of about 40-60 nm in diameter with a single stranded RNA genome of about 12,300 bases with positive polarity, classified as a pestivirus within the family Flaviviridae. Natural hosts are domestic and wild pigs. The virus causes one of the most severe diseases in pigs world wide with grave economic consequences. The clinical picture of classical swine fever is variable, depending on the age of the affected animals and viral virulence. The virus is well characterised and reliable laboratory diagnostic procedures are available. In many parts of the world live attenuated vaccines are being used as a safe and efficient prophylactic tool. However, in EU Member States and several other countries vaccination is prohibited and CSF is controlled by a strict stamping out policy. In order to overcome the disadvantages of conventional vaccination inactivated marker vaccines have been developed that enable the distinction between vaccinated and infected animals. Whether these vaccines will be accepted as an additional tool in the framework of the stamping out policy is not yet decided.