Antibody-based diagnosis of small ruminant lentivirus infection in seminal fluid

Antibody-based diagnosis of small ruminant lentiviruses (SRLVs) has been efficiently achieved using serum and milk, but not semen, for which polymerase chain reaction (PCR) has been proposed as a confirmatory technique. This work, involving 296 ovine (Ovis aries) and caprine (Capra hircus) semen donors, investigates whether seminal fluid (SF) can be reliably used in antibody-based SRLV diagnosis. First, a gold standard was established to assess the infection status and determine the sensitivity and specificity of three commercial enzyme-linked immunosorbent assays (ELISAs) in serum testing using Western blot and PCR as confirmatory tests. For SF testing, both gold standard and serum testing results were used as reference. The performance of SF testing was affected not only by the ELISA assay sensitivity (related to antigen spectrum) compared with that of the gold standard (as it occurred in serum testing) but also by SF sample quality and SF working dilution. Nonturbid SF samples, commonly collected in artificial insemination centers (AICs), were required. Compared with serum, SF testing had a decreased sensitivity in two of the ELISA assays (with original serum working dilutions ≤1/20 in serum testing) but reached a similar sensitivity (and specificity) in the assay designed to work at the highest serum dilution (1/500). A SF concentration of about 1/2 (250-fold that used in serum testing) was found optimal in this assay, yielding highly repeatable results that were in almost perfect agreement with those of serum testing (κ ± SE, 0.91 ± 0.81). Thus, SF ELISA can be reliably applied in antibody-based SRLV diagnosis. This information may be useful to control infection in AICs and animal and semen trade programs requiring health-certified quality of semen donors.