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Molecular epidemiology of BVD during the last phase of the Swedish BVD-programme presentation of a new project K. Ståhl* a , A. Lindberg b , C. Baule c , J. Kampa d , S. Bélak c and S. Alenius d .
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last phase of the Swedish BVD-programme
presentation of a new project
K. Ståhl*a, A. Lindberg b, C. Baule c, J. Kampa d, S. Bélak c and S. Alenius d.
aDept. of Biomedical Sciences and Veterinary Public Health ,SLU, Uppsala, Sweden. bSwedish Dairy Association,
cDept. of Veterinary Virology, SVA,Uppsala, Sweden, dDept. of Ruminant Medicine and Epidemiology, SLU, Uppsala, Sweden.
The Swedish BVDV eradication programme is in its last phase and by the beginning of March -04, 96% of all herds had been officially declared free.Nevertheless, new infections are being detected despite the strict biosecurity rules within the programme. The importance of indirect routes of transmission of BVDV between herds is increasing as the biosecurity meassures undertaken efficiently reduce the risk of transmission by the conventional routes.
In ≈50% of the cases where infections are detected in previously free herds the routes of transmission remain unidentified. Previous studies have shown that BVDV strains found in Sweden belong to either subgroup 1a, 1b or 1d of BVDV type 1 and that they are herd specific. This unique situation allows new infections to be traced to their origin and the routes of virus spread to be identified and cut.
The incidence rate of BVDV infections in herds detected within the BVD-programme 95- 03. Herds at risk defined as herds affiliated to the programme and not under investigation.
The characterisation and mapping of all Swedish BVDV isolates will give us a unique possibility to trace routes of infection and to survey the national BVDV situation. The molecular epidemiological approach will speed up the last phase of the BVD-programme and help to reach total eradication within stipulated time.
Material & methods
During a three-year period (2003-2005) a BVDV-bank consisting of isolates from all BVDV infected farms detected within the programme will be built up. Three specific regions of the genome, i.e. the 5'NCR, the Npro gene and the E2 gene from the isolated viruses will be analysed by means of RT-PCR and sequencing. The sequences will be used for phylogenetic analysis to seek epidemiological relationships between occurrences. If a relation is found between isolates from different herds, information will be retrieved from the data bank of the Swedish Dairy Association to trace the origin of mothers of persistently infected (PI) animals and to identify potential risk factors. This information will be used to identify relationships in time or space between the herds, and to trace routes of transmission. In case of isolation of BVDV-strains previously not described in the country, phylogenetic comparison will be performed using sequnences of known strains within the GenBank database. Introduction of foreign BVDV-strains by e.g. imported semen or embryos will thus be detected at an early stage.
Phylogram of the 5’ NCR of 15 Swedish BVDV-strains (with reference and previously described strains in bold). Strains within red ovals were isolated from animals from different herds but show phylogenetical similarities that may indicate epidemiological relationships. Within the blue oval an example of a herd specific strain.
This study is supported by the Swedish Farmers’ Foundation for Agricultural Research (SLF; Project no. 0330007)