DEVELOPMENT OF A PCR TEST TO DETECT CELL-FREE AND INTEGRATED AND MAEDI-VISNA VIRUS (MVV) AND IT'S USE TO INVESTIGATE COLOSTRAL INFECTION IN LAMBS

Abstract

A PCR test was developed to detect cell-free and cell-integrated maedi-visna virus (MVV), its degree of agreement with an LTR-PCR and an antibody ELISA of proven efficacy was analysed in colostrum samples and all three tests were employed to investigate colostral MVV infection in lambs. Primers were designed from gag gene sequences homologous in the six MVV sequences presently in GenBank, and amplify a 744bp frag- ment. 856 assays were carried out including 283 with the new gag-PCR and a good correlation was observed between the presence of cell-free and -integrated MVV. This is novel and questions the relative role of the two viral forms in MVV infection. Instead, the correlation between PCR and ELISA results was only moderate and provided further evidence that MVV detection may fail in infected animals. The PCRs detected MVV in colostrum ingested by most lambs that later tested seropositive at 10 months-old and additionally, the gag-PCR and to a lesser extent the LTR-PCR, detected MVV in colostrum taken by lambs seronegative at 10 months-old most likely because they ingested less colostrum. As well as providing further evidence of the positive association between MVV infection and volume of MVV-containing colostrum ingested, this result suggest that the gag-PCR developed is more sensitive than the LTR-PCR used in this study.