Immune response dynamics of recent and chronic small ruminant lentivirus infection in the male reproductive system

The objective of this study was to analyze the immune responses of bucks to small ruminant lentivirus (SRLV) with a focus on the reproductive system of males with recent and chronic infection. A total of 12 bucks were selected, six seronegative and six seropositive with chronic natural infection for more than 18 months (chronic infection group). After selecting the animals, the six seronegative males were intravenously inoculated with caprine arthritis-encephalitis virus (CAEV)-Co viral strain at a titer of 10-5,6 TCID50/mL. After viral inoculation, this group was called the recent infection group and was monitored weekly with the chronically infected group for 180 days with blood serum and seminal plasma Western Blot (WB) analysis. Of the animals with chronic SRLV infection, 18.94% (50/264) showed anti-SRLV antibodies in at least one of the samples, and 81.06% (214/264) were negative. Anti-SRLV antibodies were detected in 27.27% (36/132) of the blood serum samples from this group, while 10.60% (14/132) were reactive in the seminal plasma WB test. The animals inoculated with CAEV-Co became seropositive after the third week of viral inoculation. In this group, 31.06% (41/132) of seminal plasma samples had anti-SRLV antibodies, and of these, 70.73% (29/41) coincided with blood serum results. Of the remaining 29.27% (12/41), the seminal plasma sample of only three animals (RIA2, RIA3, and RIA5) had anti-SRLV antibodies. One of the animals with a recent infection presented anti-SRLV antibodies only in seminal plasma samples, possibly due to virus compartmentalization. Intermittent viral shedding was observed in both biological samples, regardless of the infection stage. The immune response in bucks with recent SRLV infection is more significant than in chronically infected animals. Regardless of the stage of infection, there is a fluctuation in antibody levels, therefore, this creates a risk of false-negative samples when performing the diagnosis.