Final phase of the Swiss CAEV eradication program: Assessment, analysis and monitoring of small ruminant lentiviruses still circulation in the goat and sheep populations

• Forschungsstelle: BLV
• Projektnummer: 1.04.08
• Projekttitel Englisch: Final phase of the Swiss CAEV eradication program: Assessment, analysis and monitoring of small ruminant lentiviruses still circulation in the goat and sheep populations

Schlüsselwörter (Englisch)

SRLV, CAEV, Maedi-Visna, Lentivirus, serology

Kurzbeschreibung (Englisch)

The continuous emergence of cases of seroconversions in goat flocks considered free of small ruminant lentivirus infections may jeopardize the very successful Swiss CAEV eradication campaign. Small ruminant lentiviruses of ovine origin appear to play an important role in these cases of seroconversions and their spread in the goat and sheep population should be tightly monitored. In a previous project supported by the BVET we have developed a new ELISA for the serological diagnosis of small ruminant lentivirus infections based on synthetic peptides encompassing an immunodominant region of the envelope glycoprotein of these viruses. Using a representative panel of SU5 peptides covering a large spectrum of viruses circulating in Switzerland we have analyzed 321 goat sera sampled in seronegative goat flocks (N- status) by Franz Brülisauer and Jürg Rüfenacht from the BVET. The results were puzzling, revealing that an important minority of these goats (~10%) reacted to at least to one of the SU5 peptides. The majority of these positive sera bound to peptides derived from viruses phylogenetically close to the Maedi-Visna group and especially to the 1163M strain that was isolated in the context of the most important case of cross-species transmission detected in Switzerland (Interlaken market show). Using the 1163-SU5 peptides we have previously shown that animals with antibody binding to this peptide, but seronegative according to the routine diagnostic tools, were infected with SRLV as demonstrated by PCR analysis and/or virus isolation. Therefore we consider that the SU5 peptides are a reliable tool permitting a large-scale serological screening of animals infected with SRLV escaping a monitoring based on routine diagnostic tools. For this granting period we propose to screen all goat sera sampled over the next two years for the compulsory CAEV test and a large panel of sheep sera for their reactivity to SU5 peptides. This will provide a clear picture of the extent of the spread of viruses that escaped the CAEV eradication campaign in goats or infecting sheep. The virological analyses of SU5 seropositive animals by PCR and/or virus isolation will permit a validation of the SU5 serology that may substitute as a confirmatory assay the more expensive and cumbersome Western Blot. This project is tightly linked to a companion project focused on experimental cross-species transmission of small ruminant lentiviruses and submitted in parallel to the BVET. The present project will provide information on the spread of SRLV still circulating in the Swiss goat and sheep population in this final phase of the CAEV eradication program, while the companion project will provide the molecular and virological details on viruses crossing the species barrier between sheep and goats. Together, the two projects will provide the necessary information to plan the final step of the eradication campaign.

Projektziele (Englisch)

Serological screening
In this project we propose for the next two years to monitor with the novel SU5 ELISA all goat sera collected in the context of the CAEV compulsory testing. Additionally, a large number of sheep sera that will be sampled by the BVET in the context of a large-scale serological assessment of Brucella infection in Switzerland will also be included in this analysis. This study will reveal the exact extent of what we called the tip of the iceberg in Fig. 1 and will provide precise indications on which animals should be selected for an in depth virological analysis that is also a pivotal part of this proposal.

Virological analysis
Animals showing strong reactions to the SU5 peptides will be selected for a virological analysis. Peripheral blood mononuclear cells isolated from the blood of these animals will be the first organ compartment to be analyzed. Additionally, selected animals will be bought to allow a post-euthanasia investigation of organ compartments such as lymph nodes, broncho-alveolar lavage cells and synovial membrane. The main goals of this part of the project will be: (i) To isolate replicating viruses and to study the properties of these particular SRLV that escaped the eradication campaign and (ii) to perform a phylogenetic analysis of these viruses that are still circulating in the goat and sheep populations. We will analyze the cellular tropism of these viruses, comparing their replication kinetics on different sheep and goat cells. Furthermore, we will assess the receptor usage of these viruses which may be restricted to cells of ruminant origin as it is the case for the prototypic CAEV viruses or may be broader, including also human cells, as for the prototypic MVV.

Umsetzung und Anwendungen (Deutsch)

UMS 2009:

Diss. wurde publiziert, Resultate fliessen in Routinediagnostik

ein. Nutzen für BVET ist erreicht. Umsetzung ist erfolgt

 Status: erledigt (mvo)

Publikationen / Ergebnisse (Deutsch)

Schlup, B. (2009) SU5-Peptid-ELISA als zusätzliches Bestätigungsverfahren für die SRLV-Diagnostik. Dissertation, Institut für Veterinär-Virologie der Universität Bern.

29.10.2009: Umsetzungssitzung 2009: Diss. wurde publiziert, Resultate fliessen in Routinediagnostik ein. Nutzen für BVET ist erreicht. Umsetzung ist erfolgt. Neuer Status: „erledigt“ (mvo).

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