We conducted a study on 81 initially bulk-milk ELISA negative dairy herds taken from a random sample of Dutch dairy herds to evaluate variation in bulk-milk S/P ratios and to study reasons for bulk-milk conversion. These herds were repeatedly (3-month intervals) tested between April 2004 and August 2005 and serostatus of all animals had previously been established as negative (N), low-positive (LP) or high-positive (HP). Of these herds, herd- and test-related factors associated with variation in sample over positive (S/P) ratios were analysed using a multivariable linear-mixed model with ‘herd’ as random effect. In addition, changes of animal serostatus in converting herds were described. S/P ratios were calculated as the optical density of the bulk-milk sample minus the optical density of the negative serum control divided by the difference in optical density between the positive and negative serum control.
Sixteen bulk-milk conversions in 12 dairy herds were seen with few indications of serological conversion in lactating cattle except for one herd in which recrudescence of infection appeared likely in nine cows. The effect of HP serostatus on bulk-milk S/P ratio was 2–3 times stronger compared with LP serostatus. In addition, bulk-milk S/P-ratio increased when the proportion of HP animals between 1 and 60 days in milk increased and decreased when the average milk-production level of the herd increased. Besides these herd-related factors, the use of different ELISA-testkits between test rounds had a significant effect on the S/P-ratio in bulk-milk samples. 相似文献
OBJECTIVE: To investigate the seroprevalence of Neospora caninum infection in a commercial dairy cattle herd, 15 months after detection of an abortion outbreak. PROCEDURE: Sera from the whole herd (n = 266) were examined for N caninum antibodies by indirect fluorescent antibody test (IFAT) and immunoblot analysis. Herd records were reviewed to collate serological results with abortion history, proximity to calving, and pedigree data. RESULTS: The seroprevalence of N caninum infection was 24% (63/266) for IFAT titre > or = 160, 29% (78/266) for immunoblot positive (+ve), and 31% (82/266) for IFAT > or = 160 and/or immunoblot +ve; 94% (59/63) of animals with IFAT > or = 160 were immunoblot +ve. The association between seropositivity (IFAT > or = 160 and/or immunoblot +ve) and history of abortion was highly significant (P < 0.001); the seroprevalence was 86% (18/21) in aborting cows, compared with 30% (50/164) in non-aborting animals. The abortion rate for seropositive cows was 26% (18/68) compared with 3% (3/117) for seronegative animals. IFAT titres of infected cows were higher within 2 months of calving than at other times (P < 0.001). The association between seropositivity in dams and daughters was highly significant (P = 0.009). CONCLUSIONS: The abortions were associated with N caninum infection and there was evidence of reactivation of latent infection close to calving and congenital transmission of infection. Immunodominant antigens identified by immunoblots may prove useful for improved diagnostic tests. 相似文献
Microneme proteins (MICs) are important for Apicomplexan parasite invasion due to their adhesion to host cells. Several studies have indicated that Neospora caninum MIC3 and MIC8 are important adhesion factors and potential vaccine candidates against neosporosis. In this study, we evaluated the protective efficacy of recombinant proteins and DNA vaccines of NcMIC3 and NcMIC8. BALB/c mice were immunized with rNcMIC3, rNcMIC8, pcDNA3.1-NcMIC3 and pcDNA3.1-NcMIC8 respectively, and challenged with N. caninum tachyzoites. The immune responses were evaluated through cytokine, antibody measurements and the parasite burden in the mice brain tissues. Serological analysis showed that recombinant protein vaccines induced higher levels of immunoglobulin G (IgG) than other groups. The percentage of IgG1 and IgG2a in the recombinant protein groups was higher than the other groups, and with a predominance of IgG1 over IgG2a, suggesting that recombinant protein vaccines elicited a Th2-type immune response, while DNA vaccines mainly produce a Th1-type immune response. In addition, mice immunized with rNcMIC3 and rNcMIC8 a had lower parasite burden in brain tissue compared with the other groups. These results demonstrate that rNcMIC3 and rNcMIC8 could induce humoral and Th2-type immune response, leading to a considerable level of resistance against neosporosis. 相似文献
We used a prospective seroepidemiological approach to investigate endemic abortion in a dairy herd in Arequipa, Peru, and its association with Neospora caninum and bovine viral-diarrhoea virus (BVDV) infections. Between January 2002 and March 2004, 1094 pregnancies were confirmed in 538 cows. Of these, 137 pregnancies (13%) in 121 cows ended in abortion. The serological status to N. caninum was assessed using a single serological screening, whereas BVDV status was assessed at the herd level through consecutive samplings of young stock.
Cox proportional-hazards models were used to estimate the effect of N. caninum and BVDV on the hazard of early (between day 42 and day 100 in gestation), and late (after day 100) abortions, respectively. Serological status to N. caninum was included as a dichotomous variable, and the effect of BVDV estimated at the herd level, as a time-dependent seasonal effect. Because data from repeated pregnancies were included, we considered possible lack of independence between observations and included frailty effects into the models. Our models also considered the possible confounding by parity and animal origin.
Only multiparity was associated with the hazard of early abortion (HR = 2.8 compared to nulliparous heifers). N. caninum seropositivity significantly affected the hazard of late abortion, but interacted with parity. The HRs for Neospora-positive animals were 6.4, 3.7 and 1.9, respectively, for nulliparous heifers, first-lactation cows and multiparous cows. Evidence of BVDV circulating (or not) among the young stock was not associated with abortions, but few cows in this herd were susceptible to incident infection. 相似文献
The protozoan parasite Neospora caninum is a major cause of abortion in cattle throughout the world. In the process of propagating Neospora in vitro and producing specific antibodies for development of diagnostic assays in the food supply, our laboratory identified the presence of bovine antibodies to N. caninum in fetal bovine sera. The sera were produced commercially and preferentially recommended for tissue culture use and monoclonal antibody production. Seventeen different fetal bovine serum samples of different grades and from four different companies were examined for the presence of total IgG, IgG1, IgG2, and IgM specific for N. caninum. All of the tested serum samples recognized N. caninum specific bands on Western blot. Low IgG serum also recognized these antigens but with lower intensity. Antibody response was also evaluated using a commercially available ELISA kit for N. caninum. 相似文献
