Experimental neosporosis in bulls: Parasite detection in semen and blood and specific antibody and interferon-gamma responses

Abstract

Aim: To investigate the presence of Neospora caninum in semen and blood, and the development of specific antibody and interferon-gamma (IFN-g) responses in experimentally infected bulls. Methods: Eight bulls were intravenously infected with 10 8 live N. caninum tachyzoites of NC-1 isolate. The presence of N. caninum in semen and blood was assessed using a nested-PCR procedure. PCR-positive semen samples were bioassayed using a BALB/c nu/nu mouse model. Specific anti-N. caninum antibody and IFN-g responses were also examined. In parallel, eight seronegative bulls were studied as non-infected controls. All bulls were monitored for 26 weeks. Results: All eight experimentally infected bulls showed N. caninum DNA in their semen and/or blood samples at some time during the course of the study. Parasite load in semen ranged from 0.1 to 14.5 parasites/ml (mean 6.0). N. caninum could not be detected in BALB/c nu/nu mice inoculated with PCR-positive semen samples. A significant increase in mean serum specific IgM antibody response to N. caninum was detected between 10 and 28 days post-infection (p.i.). Serum specific IgG, IgG1, and IgG2 antibody levels in experimentally infected bulls were significantly different after 21, 10, and 14 days p.i. as compared to controls, respectively. Specific anti-N. caninum IgG were detected in seminal plasma from infected bulls and values obtained were different from controls after 25 days p.i. Mean specific IFN-g responses in experimentally infected bulls were significantly higher than controls 3 days p.i. Conclusions: This is the first study to report the presence of N. caninum DNA in the semen and blood of experimentally infected bulls. Our observations indicate an intermittent presence of N. caninum in low numbers in semen and associated with chronic stage of the infection. This study is also the first to report the detection of anti-N. caninum IgG in seminal plasma of experimentally infected bulls. #

Effects of re-infection with Neospora caninum in bulls on parasite detection in semen and blood and immunological responses

“…Six of the bulls were infected 10 months before with 10 8 tachyzoites of N. caninum [3] and the other three were non-infected. Bulls were allocated into three groups (A-C) composed of three animals each.…”

“…Group C included non-infected control bulls. Tachyzoites used for experimental infections and infection procedure were described previously [3]. The presence of N. caninum DNA in semen and blood, serological (IgG, IgG1, IgG2, and IgM) and IFN-g responses, and specific IgG and IgA levels in seminal plasma of bulls was assessed.…”

“…Sample collection and preparation was previously explained [3]. For the bioassay in heifers, a weekly pooled semen sample was prepared with excess semen collected from each bull from groups A and B.…”

“…The bioassay procedure was previously described [2,3]. In parallel, experimental infections were done with bovine semen artificially contaminated with different quantities of N. caninum tachyzoites of the NC-1 strain using BALB/c nu/nu mice to assess the capability of the parasite to induce an infection within this animal model in order to assess the sensitivity of this bioassay methodology.…”

“…The presence of N. caninum DNA in fresh semen of naturally [2] and experimentally [3] infected bulls was intermittent and the parasite load was low (0.1 and 14.5 parasites/ml of semen). A recent experimental study showed that the intrauterine infection via contaminated semen using 5 Â 10 4 tachyzoites caused persistent serum-specific antibody responses in some www.theriojournal.com Available online at www.sciencedirect.com Theriogenology 69 (2008) [905][906][907][908][909][910][911] heifers [4].…”