Development, validation and evaluation of added diagnostic value of a q(RT)-PCR for the detection of genotype A strains of small ruminant lentiviruses.

Small ruminant lentiviruses (SRLV) infect sheep and goats. Diagnosis of SRLV infection mostly relies on serological testing but more recently, also PCR is regarded as a useful complementary tool in SRLV diagnosis. The goal of this study was to develop and validate a quantitative PCR capable to detect a broad range of SRLV strains from genotype A, including strains circulating in Belgium. The developed q(RT)-PCR targets a region of the gag gene and showed to be highly sensitive and specific with a limit of detection of 6 DNA and 40 RNA copies/reaction respectively. SRLV sequences could be detected in lung samples and leukocytes pellets. The q(RT)-PCR identified SRLV positive animals in Belgian sheep flocks, but also SRLV isolates and samples from Scotland, The Netherlands, Spain, Portugal, UK, Iceland, Finland and USA were found positive. Samples known to contain 'CAEV like' SRLV from France and Spain were not identified as positive. Combined serological and PCR analysis of a limited number (n=35) of Belgian sheep underlined the usefulness of the described PCR as a complementary diagnostic tool since 3 seronegative animals were found positive by the PCR. In conclusion, the validated q(RT)-PCR shows excellent analytical characteristics and is capable to detect SRLV strains belonging to genotype A from various countries.