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Improved diagnosis of swine vesicular disease (SVD)

Contract nr: FAIR-CT96-1545
Project nr: 1545
Project type: SC
Starting date: 01/02/1997
Duration: 42 months
Total cost: 1,796,482 EUR
EC Contribution: 1,287,000 EUR
Scientific Officer: Isabel MINGUEZ-TUDELA
Research topic: Animal health
Acronym: Improved diagnosis of SVD

Background:
Swine Vesicular Disease (SVD) is a disease of increased prevalence and economic significance in EU Member States. An OIE Category list A disease, SVD is highly contagious and rapidly spread by direct contact with infected pigs and by contamination of the environment. Its eradication within the EU is a priority objective of the Member States.
Current diagnosis of SVD, based on conventional serological methods, does not allow enough confidence in screening of animals and needs to be improved. The proposed study directly complies with a priority objective of the Agricultural and Fisheries work programme (4. 4 Animal and Plant Health, Animal Welfare), as one of the research tasks of this programme is the development of improved diagnostic tests, including application of bio-technology, and systems for zoonoses and diseases of economic significance (4.4.2).

Objectives:
The goals of this project are to investigate and develop re-agents and methods which will improve the diagnosis of swine vesicular disease (SVD). In particular, the `singleton reactor' phenomenon will be specifically addressed. We will also investigate those aspects of viral pathogenesis which affect the effectiveness of control programs for the disease, such as the persistence of SVD virus in pigs and the cells involved in early infection.

Description:
The specific objectives are:

1) To improve virus detection. Accurate and versatile ELISA and PCR techniques for the detection of small traces of SVD virus in nasal swabs, faeces and tissues will be developed. In situ hybridisation and in-situ PCR will be optimised to detect virus in post-mortem organs. SVD virus isolates will be characterised to identify the origin of new outbreaks, patterns of spread and viral evolution.

2) To improve serology. Novel and simple ELISA based on recombinant and synthetic antigens will be developed and validated. We will also develop novel techniques to detect SVD virus-specific cellular immune response and serological methods, including isotype (igg/igm) analysis of the sera to study the evolution of the disease.

3) To study viral pathogenesis.

The application of the above techniques will be applied to study the duration of SVDV infection as well as the identification of cells and organs involved in viral persistence. The use of biotechnology to develop more specific, sensitive and cost-effective diagnostics will result in quicker diagnosis of SVD infections and hopefully the resolution of the singleton reactor phenomenon. Rapid and accurate diagnosis of SVD will limit the potential spread of disease to other animals, thus maintaining animal well-being. In addition, the use of recombinant or synthetic antigens will eliminate the need for mass production of susceptible cell cultures for production and purification of SVD antigens.
A range of established technological expertise necessary for completion of the project is spread out throughout the network of participating partners. In addition, excellent training opportunities for scientists in these new disciplines will be provided.


Current situation/results:
Different panels of Mabs have been selected to detect and classify all antigenic variants of SVDV, and one Mab has been proven to be useful as an universal detector for the identification of SVDV in pathological samples.

An overall view the work carried out on the PCR methods suggest that in field conditions the standard PCR assay is more suitable than the immuno-PCR to perform multiple assays. However, newly developed improved protocols of PCR-ELISA seem to be promising because it is faster and more sensitive than both standard PCR and virus isolation.

The virus bank contains all the isolates from the new and old outbreaks, and most of them are molecularly and antigenically characterised. The results indicate that all Italian isolates from 1993 to 1998 belong to the same group (Group IV). The same group of viruses were isolated in Italy during the period 1988 to 1992 and were responsible for the outbreaks of SVD in the Netherlands, Portugal and Spain during the early 1990's. The isolates from the outbreaks of Taiwan 97, Taiwan 98, Hong Kong 80's and 90's, belong to a subgroup within Group IV. Finally, the recent European SVDV probably have a common origin with viruses from the Far East.
The development of a method for the detection of cytokines by T-cells in response to SVDV has been difficult due to technical problems. However, the protocol is set up for several cytokines. This method could be very useful as an alternative for the diagnosis of SVD, as it is for other animal infections, and it could be possible to perform the assay using recombinant or synthetic SVDV antigens.

All the results derived from the work with recombinant SVDV antigens indicate that these polypeptides are not suitable for use in diagnosis. The majority of antibodies induced by infection with SVDV are to conformational, discontinuous epitopes. However, the recombinant P1 protein is recognised by, and induces antibody almost exclusively to the linear, sequential epitopes of capsid. Therefore, it is not recognised by the majority of antibodies induced during SVDV infection.

Accordingly, although the capsid precursor polyprotein P1 is highly immunogenic, it does not induce neutralising, protective immunity in pigs. If synthetic antigens and immunogens are to be produced they must therefore mimic conformational rather than linear determinants.

Finally, the study of the singleton reactor phenomenon has provide interesting results. The data obtained during this year indicate that it is possible to find the conditions to reduce the detection of SR by at least 50%.

Website: http://www.iah.bbsrc.ac.uk/svd_project/
The common username is: "singleton" and the password is "pigswill"


Coordinator
Victoria LEY
I.N.I.A.
Carretera Coruña Km 7.5
E-28040 Madrid
Tel: +34 91 620 23 00
Fax: +34 91 620 22 47
E-mail: ley@inia.es


Partners

  • Alastair DOUGLAS
    The Queen's University of Belfast
    Stoney road
    UK-BT4 3SD Stormond - Belfast
    Tel: +44 1232 52 56 39
    Fax: +44 1232 52 57 73
    E-mail: a.douglas@qub.ac.uk

  • Emiliana BROCCHI
    Istituto Zooprofilattico Sperimentale della Lombardia e Dell'Emilia
    Via Antonio Bianchi 7
    I-25124 Brescia
    Tel: +39 030 229 03 10
    Fax: +39 030 22 56 13
    E-mail: ebrocchi@bs.izs.it

  • Kris DE CLERCQ
    Veterinary and Agrochemical Reseach Centre (VAR)
    Groeselenberg 99
    B-1180 Bruxelles
    Tel: +32 2 375 44 55
    Fax: +32 2 375 09 79
    E-mail: krdec@var.fgov.be

  • Aldo DEKKER
    ID-DLO - Institute for Animal Science and Health
    Houtribweg 39
    P.O. Box 65
    NL-8200 AB Lelystad
    Tel: +31 320 23 82 38
    Fax: +31 320 23 86 68
    E-mail: a.dekker@id.dlo.nl

  • Nick Knowles
    The Institute for Animal Health
    ASH Road - Pirbright
    UK-GU24 0NF Pirbright - Woking
    Tel: +44 1483 23 24 41
    Fax: +44 1483 23 26 21
    E-mail: nick.knowles@bbsrc.ac.uk

 
 
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