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Classical swine fever (CSF) is a highly contagious swine-specific disease which may have a huge economic impact for porcine production. CSF is caused by a virus belonging to the Pestivirus genus, which has expanded for the past 5 years with the discovery of new species whose genetic proximity to the CSF virus could further complicate laboratory diagnosis. The various forms of the disease, and in particular the increased frequency of attenuated forms, linked to an evolution of CSF virus strains towards a reduction in their virulence, delay clinical diagnosis. Thus, a long period may elapse before an outbreak is detected, allowing the virus to circulate longer, with the risk of spreading to distant geographical areas. Efforts must be maintained in terms of surveillance and diagnostic tools development in order to detect CSF virus infection early and thus limit the spread of the disease and facilitate control measures.

Authors used a wild strain of classical swine fever virus Alfort A19, grown on PK15 cell culture. Virus is concentrated by ultrafiltration technique, inactivated with glycidaldehyde and then mixed with an oil adjuvant. Results have brought into evidence the absolute innocuousness of this vaccine and animals given 2 doses of 2.5 ml or 1 dose of 5 ml were resistant to a challenge 2 months after vaccination. Protection lasts one year, at least.

An improved technique for the detection of hog cholera virus (HCV) neutralizing antibodies is described, in which running of the test is greatly facilitated by use of a cytolytic strain of HCV. This strain was isolated from persistently infected IB-RS 2, and was shown to induce a distinct cytopathic effect in several pig kidney cell lines (Laude, 1978). For the assay, serum samples at 1 : 10 are diluted serially twofold in disposable microplates, then 1 x 10(4) PFU of the virus-stock are added in each well. Trypsinized RP-TG cells are dispensed at 2 x 10(4)/well after 1 hour contact at 38 degrees C. After 4 days of incubation at 38 degrees C, plates are sequentially stained with neutral red and lugol, to make the undestroyed monolayers visualized. Neutralizing titre is expressed as the highest dilution of the serum affording a 75 percent protection of monolayer. This procedure has proved to be a labor saving technique yet being as reproducible and as sensitive as the immunofluorescence-tests. It combines the following advantages: 1) The immunofluorescence step is suppressed. 2) Results can be recorded without the aid of microscope. 3) The test is miniaturized. 4) Cultures of continuous cell lines are used. 5) The challenge virus is attenuated for the pig. Therefore this technique can be recommended for routine serological survey of the HCV-infection in pig-herds.

The effects of an acute Hog Cholera Virus (HCV) infection upon immune functions of experimentally infected pis were studied. Leukopenia was found to occur in both vaccinated and non-vaccinated infected animals but without any decrease in lymphocyte proportion. Lymphocytes from infected pigs had an altered response to phytohemagglutinin (PHA) as judged by an in vitro tritiated thymidine uptake of PHA-stimulated lymphocyte cultures. The beginning of a secondary humoral immune response to lysozyme appeared to be significantly depressed in HCV diseased animals.

Swine fever virus neutralization have been studied by the following method: variable plaque forming units numbers are mixed with a predetermined serum dilution. Infectivity is measured before (VO) and after (Vr) neutralization reaction. Neutralization index (N.I. = logVo/V) represent the difference between the two titers. It had been demonstrated that mass law is a good approximation to describe swine fever virus neutralization. So the most useful form in which to express the relation between N.I. and dilution logarithm (log D) is NI = NIo--K log D (I) where K is the constante corresponding to the slope of neutralization curve. A sligh K variation is observed according to immunoglobulin classes sharing antibody activity. Average K value is equal to 3. NIO is the NI obtained when extrapolating the curve to log D = o. These results have permitted to compare the two seroneutralization methods commonly used: "constant serum" method and "variable serum" method (determination of serum dilution inhibiting 50% of infectivity: D50). From formula (I) the following relation can be obtained: see formular. Theoretical and experimental log D50 values were appromaximatively the same (difference inferior or equal to 0.3). So D50 can be calculated by both methods.

This paper deals with the comparative development of active immunity in young pigs which were born from unvaccinated sows and from recently vaccinated sows. The development of immunity is expressed by the neutralizing serum antibody titer and protection against a pathogenic virus. The results show that: --the post-vaccinal increase in antibodies is inversely proportional to the titer of passive antibodies at the time of vaccination, --protection at the end of economic life depends on the antibody titer at the time of the challenge, --young pigs born from a mother which is not immune can be vaccinated starting at the age of 7 days, --the percentage of protection at the end of economic life of vaccinated baby pigs with colostral antibodies ranges from 50% when the vaccination was carried out at the age of 7 days to 100% when the vaccination occurs at the age of 2 months.

The vaccination of young piglets, with or without passive antibodies of colostral origin, was studied using the Thiverval strain. The various experiments, carried out under practical conditions, allowed us to observe the following phenomena:--in piglets without immunity of maternal origin we observed a classic primary reaction, with vigourous, lasting production of antibodies and resistance to the challenge;--in piglets with immunity of maternal origin, depending on when the vaccination was administered, the production of primary antibodies was non-existent or deficient; however, we noted that piglets vaccinated 35 days after birth resist the challenge.

Résumé: La peste porcine classique (PPC) est une maladie très contagieuse, spécifique des suidés, qui continue à constituer une menace pour la production porcine malgré un statut indemne de la plupart des pays de l'Union européenne. La PPC est causée par un virus de la famille des Flaviviridae appartenant au genre Pestivirus , en extension depuis les cinq dernières années avec la découverte de nouvelles espèces, notamment chez le porc ou autres animaux de rente dont la proximité génétique avec le virus de la PPC pourrait davantage compliquer le diagnostic de laboratoire. La diversité des formes de la maladie, et notamment la fréquence accrue des formes atténuées et inapparentes liée à une évolution des souches du virus de la PPC vers une réduction de leur virulence, retarde le diagnostic clinique. Ainsi, une longue période peut s'écouler avant la détection d'un foyer, permettant au virus de la PPC de circuler plus longuement, avec le risque de diffuser vers des zones géographiques éloignées des premiers cas d'infection. Les efforts doivent être maintenus en termes de surveillance et de développement d'outils de diagnostic afin de détecter précocement une infection par le virus de la PPC et ainsi limiter la propagation de la maladie et faciliter les mesures de contrôle. Classical swine fever (CSF) is a highly contagious swine-specific disease which may have a huge economic impact for porcine production. CSF is caused by a virus belonging to the Pestivirus genus, which has expanded for the past 5 years with the discovery of new species whose genetic proximity to the CSF virus could further complicate laboratory diagnosis. The various forms of the disease, and in particular the increased frequency of attenuated forms, linked to an evolution of CSF virus strains towards a reduction in their virulence, delay clinical diagnosis. Thus, a long period may elapse before an outbreak is detected, allowing the virus to circulate longer, with the risk of spreading to distant geographical areas. Efforts must be maintained in terms of surveillance and diagnostic tools development in order to detect CSF virus infection early and thus limit the spread of the disease and facilitate control measures. [ABSTRACT FROM AUTHOR]

Infection of PK15 cells with various strains of Hog Cholera (HCV, togaviridae) induces a transient refractory state to VSV. The reverse plaque procedure is convenient for HCV titration of virulent, "chronic" and attenuated strains.

A swine fever epizootic decimated the pig herds in villages within the Yamba focus of human trypanosomiasis. Ecological studies of Glossina palpalis palpalis populations were carried out in one of the villages for four years following the disappearance of the pigs, which had been the principal nutritive host of the Glossina in the area. One important behavioural modification occurred, namely the establishment of a small peridomestic tsetse population. The flies deserted the patches of residual forest to settle around the periphery of the village. This probably occurred in numerous other villages where the epizootic had destroyed the herds of pigs. The modified behaviour has increased the man-fly contact, but, on the other hand, facilitates vector control.

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