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

Abstract

Three bulls with experimentally induced primary infection with Neospora caninum were re-infected intravenously with 10 8 live N. caninum tachyzoites of the NC-1 isolate at 300 days post-infection to investigate the presence of N. caninum in semen and blood, and the associated immune responses. In parallel, three bulls with experimentally induced primary infection with N. caninum and three noninfected bulls were also monitored. Re-infected and infected bulls showed an intermittent presence of N. caninum DNA in semen with a parasite load ranging from 0.1 to 15.6 (mean 4.4) and 0.1 to 11.1 (mean 4.1) parasites/ml, respectively. Re-infected bulls showed significant and persistent serum-specific IgM and IgG antibody responses. Specific IgG levels were detected in seminal plasma of all infected bulls, but the magnitude of the response was significantly higher in re-infected rather than in chronically infected animals. The mean specific IFN-g levels in re-infected bulls were significantly increased as early as 3 and 7 days after experimental infection when compared to bulls in other groups. This study showed that the intermittent presence and parasite load of N. caninum in the semen of reinfected bulls is very similar to that reported in chronically infected animals. The protozoa could not be isolated from BALB/c nu/nu mice inoculated with PCR-positive semen samples and inseminated heifers with pooled semen samples did not show seroconversion. Plasma IFN-g level seems to be a good indicator of a recent N. caninum infection.

Detection of Neospora caninum DNA in semen of experimental infected rams with no evidence of horizontal transmission in ewes

“…Studies in bulls have shown a similar intermittent pattern of shedding of N. caninum DNA that has continued for more than a year (Serrano-Martinez et al, 2007a;Ferre et al, 2008). By comparison with the closely related protozoan T. gondii, DNA of this organism was also detected in the semen of experimentally infected rams up to 1-month post infection (Teale et al, 1982) which indicates a similar time frame to that seen with N. caninum in the present study.…”

“…It is unclear from this current study whether the parasite DNA detected in the semen represents viable tachyzoites as bioassay was not employed to determine if viable tachyzoites were present. In previous studies with experimentally infected cattle, viable tachyzoites could not be detected in bull semen by bioassay (Ferre et al, 2005(Ferre et al, , 2008.…”

“…While studies using AI had shown that cows were able to be infected using spiked semen (Serrano et al, 2006;Serrano-Martinez et al, 2007b), a natural mating study using experimentally infected bulls failed to induce seroconversion in the mated cows (Osoro et al, 2007) and these authors hypothesized that the parasite loads in the semen were too low to lead to infection. N. caninum DNA equivalent to 1-16 N. caninum t/ml has been detected in the semen of both naturally and experimentally infected bulls (OrtegaMora et al, 2003;Caetano-da-Silva et al, 2004;Ferre et al, 2005;Serrano-Martinez et al, 2007a;Ferre et al, 2008). Assuming the mean volume of ejaculate is approximately 9-10 ml (Chenoweth, 1983) this represents <200 tachyzoites per ejaculate.…”

“…Transmission of N. caninum via semen was thought to be possible when bulls were found to be seropositive towards N. caninum and N. caninum DNA was detected in the semen of naturally (Moore et al, 2003;Ortega-Mora et al, 2003;Caetano-da-Silva et al, 2004;Ferre et al, 2005) and experimentally infected bulls (Serrano-Martinez et al, 2007a;Ferre et al, 2008). Dose dependent seroconversion and parasitaemia were also seen in heifers inseminated with semen spiked with N. caninum tachyzoites, though no seroconversion or detection of N. caninum DNA in the embryo or calves was observed (Serrano et al, 2006;SerranoMartinez et al, 2007b).…”

Seroprevalence and risk factors associated to Neospora caninum in dairy cattle herds in the municipality of Pasto, Colombia

“…Experiments conducted in the U.S. showed that venereal transmission is possible with a large number of tachyzoites (26). In this study, two out of three bulls sampled were seropositive for antibodies to N. caninum.…”