1. Test materials and methods
1.1 Test materials
1.1.1 Test animals A 1600-head basic sow herd scale farm in Guangdong was randomly selected 100 serum samples for testing each time.
1.1.2 Test reagents ELISA kit for antibody detection of swine fever and ELISA kit for antibody detection of blue ear disease (both products of IDEXX Company, USA).
1.1.3 Main test instruments: micro-sampler; Elx800 enzyme labeling instrument.
1.1.4 Vaccines: weak vaccine for swine fever (transmissible cell source); weak vaccine for highly pathogenic porcine blue-ear disease (JXA1-R strain)
1.2 Test methods
Blue-ear and swine fever vaccines were used in the way of general immunization: once in 3 months, 4 times a year. All male and female pigs were immunized with 2 doses of swine fever vaccine in the first week of January, April, July and October, and all male and female pigs were immunized with 2 doses of blue ear vaccine (JXA1-R strain) in the first week of February, May, August and November. Piglets were immunized with 1 dose of blue-ear vaccine at 2 weeks of age, and 1 and 2 doses of swine fever vaccine at 4 and 9 weeks of age, respectively. In this experiment, after the whole farm was immunized with blue ear vaccine for the first time in November 2012, the antibody levels of blue ear and swine fever were detected on the 25th of January, April, July and October in 2013, and blood was collected from 30 boars, 100 sows were randomly selected for testing, and 50 piglets were randomly selected for testing at 7 and 12 weeks of age. 2013 was the first year in which the farm had a high number of heavy sows and a low number of piglets. The proportion of abortions in sows with heavy fetuses in this farm reached 8%, the proportion of stillbirths in fetuses produced reached 12%, and the nursery pigs lost weight, coughed, and had a mortality rate of 15%.
1.3 ELISA test methods and judgment standards
ELISA test methods and judgment standards, refer to the instructions and standards of IDEXX Company's kits. The ELISA test for swine fever antibody was established under the condition that the average OD450 value of negative control was >0.5 and the blocking rate of positive control was >50%. Judgment criteria: blocking rate <40% is negative; 40% ≤ blocking rate ≤ 50% is suspicious; blocking rate >50% is positive. S/P ratio of Blue Ear Antibody Detection (IDEXX) ELISA: S/P< 0.4 Negative; 0.4 ≤ S/P ≤ 2.5 Weakly virulent vaccine infection, antibody production; S/P> 2.5 Wild virulent infection, antibody production.
1.4 Statistical processing
Test data were analyzed statistically by SPSS13.0 software, and the statistical results were expressed as "mean ± standard deviation", and analyzed by ANOVA and multiple comparisons by LSD method.
2 Results
2.1 As shown in Figure 1, 0.4 ≤ S/P ≤ 2.5 is the antibody produced by the weak blue-ear vaccine infection; S/P>2.5 is the antibody produced by the wild blue-ear infection. The positive rate of blue-ear antibody of boars reached 94%, and the proportion of wild-virus infection reached 63%; the positive rate of blue-ear antibody of parturient sows reached 95%, and the proportion of wild-virus infection reached 61%; the positive rate of blue-ear antibody of 7-week-old and 12-week-old piglets reached 99%, and the proportion of wild-virus infection reached 70%. As can be seen in Figure 2, the dispersion of blue ear antibody of boars was 52%, and the average value of antibody was 2.82; the dispersion of blue ear antibody of farrowing sows was 47%, and the average value of antibody was 2.85; the dispersion of blue ear antibody of 7-week-old and 12-week-old piglets was 43%, and the average value of antibody was 2.99. The results showed that all pigs were infected by wild toxin, and the weakly virulent vaccine of blue ear could not play a protective role against blue ear in this pig farm. The results showed that all pigs were obviously infected with blue-ear wild-virus, and the blue-ear weak-virus vaccine could not protect the farm against blue-ear disease.
2.2 As can be seen from Figure 3, swine fever antibody blocking rate >50% is a positive value. The positive rate of antibody to swine fever in boars reaches 44%; the positive rate of antibody to swine fever in parturient sows reaches 52.7%; the positive rate of antibody to swine fever in 7-week-old and 12-week-old piglets reaches 57.5%. As shown in Figure 4, the dispersion of antibodies to swine fever in boars was 37%, and the average antibody value was 53.2%; the dispersion of antibodies to swine fever in parturient sows was 37%, and the average antibody value was 51.8%; and the dispersion of antibodies to swine fever in 7-week-old and 12-week-old piglets was 42.5%, and the average antibody value was 55.2%. The results showed that the antibody level of swine fever in the whole farm was low, the dispersion was not satisfactory, and the protection rate of swine fever for the whole herd was not high.
3. Discussion
The effect of the weak porcine blue ear disease vaccine on the immune antibodies to swine fever through the analysis of the results of this test found that the immunization of the weak highly pathogenic porcine blue ear disease vaccine (JX-A1-R strain) Blue Ear Feral Virus (BEFV) infection rate after immunization was as high as 64%, and the average value of the blue ear antibodies, S/P, were all more than 2.5, which indicated that the blue ear virus in this farm was more active and already infected with the BEFV, indicating that this vaccine could not effectively control the BEFV in this farm. This indicates that the vaccine is not effective in controlling blue ear disease. The average value of antibody positive rate of swine fever is only 77%, and the average value of antibody dispersion is only 39%, both indicators are poor, indicating that the antibody of swine fever is unqualified. Therefore, we can learn that immunization with the highly pathogenic porcine blue ear disease weak vaccine (JX-A1-R strain) had an obvious interfering or inhibiting effect on immunization with swine fever cellular vaccine. This is basically consistent with Zhang Fenghua et al. who reported that immunization with a weakly virulent porcine blue ear disease vaccine had a significant interfering effect on the immunization effect of swine fever. This is likely to be related to the pathogenesis of the blue ear disease virus, which binds to the receptor of alveolar macrophages during replication, leading directly to the fragmentation and lysis of alveolar macrophages and delaying the processing and presentation of antigens by alveolar macrophages, thus leading to immunoregulatory disorders in the host. At the same time, the blue ear disease virus acts on the T-lymphocytes of the immune system, causing a decrease in the ratio of each subpopulation of T-lymphocytes, thus suppressing the body's immune response to other pathogens. At the same time, the blue ear disease virus also has "antibody-dependent enhancement", and inhibits the production of immune antibodies against swine fever vaccine, which shows that the immunization against blue ear disease vaccine is a double-edged sword, with both advantages and disadvantages. According to Du Xizhong et al, the immunization interval time of 7d between the two vaccines still has obvious interference effect. Therefore, pig farms should decide whether or not to immunize with the weak blue ear vaccine according to their actual situation. In the 2013 Li Mann World Pig Conference, Prof. Yang Hanchun, academician of the Academy of Engineering, clearly pointed out that we should use less blue-ear virus vaccine, and even less blue-ear virus vaccine of different strains (blue-ear virus is prone to mutation and recombination), and we should use purification to control blue-ear disease. Now this point of view has been recognized by the vast majority of experts, scholars and managers of large-scale pig farms.