Seroprevalence-specific rates of unvaccinated pigs.
A total of 129 unvaccinated pigs from eight regions were sampled for testing CSFV antibody, and 77.5% (100/129) were positive for CSFV (Table 1). Furthermore, 0 (0/10) and 100% (4/4) in the regions of Chenzhou and Yueyang were the positive rates for CSFV as a minimum and maximum, respectively, and the seropositivity of CSFV between the sample locations (n = 8) was statistically significant by using chi-square test (χ2 = 43.648, df = 7, p < 0.001). The results showed that no CSFV infection on fattening pigs (0/10), whereas all the positive CSFV samples were from the piglets (100/100). It is worth to note that CSFV antibody in piglets decreased gradually with increase of piglets' age (Fig. 2A).
Table 1
Seroprevalence-specific rates of CSFV/PRRSV in pigs by sampling location
Category | CSFV antibodies test | PRRSV antibodies test |
Positive no. / No. of unvaccinated pigs sampled (positive rate) | Positive no. / No. of immune pigs sampled (positive rate) | Positive no. / No. of unvaccinated pigs sampled (positive rate) | Positive no. / No. of immune pigs sampled (positive rate) |
Changsha | 2/4 (50%) | 93/122 (76.2%) | / | 111/126 (88.1%) |
Hengyang | 8/10 (80%) | 128/152 (84.2%) | 76/151 (50.3%) | 17/23 (73.9%) |
Shaoyang | 20/27 (74.1%) | 112/139 (80.6%) | 48/93 (51.6%) | 68/73 (93.2) |
Yueyang | 4/4 (100%) | 259/299 (86.6%) | 6/9 (66.7%) | 228/270 (84.4%) |
Changde | 54/60 (90%) | 364/449 (81.1%) | 116/310 (37.4%) | 255/320 (79.7%) |
Yiyang | 4/5 (80%) | 33/39 (84.6%) | 33/35 (94.3%) | 23/24 (95.8%) |
Chenzhou | 8/9 (88.9%) | 65/88 (73.9%) | 27/38 (71.1%) | 53/59 (89.8%) |
Yongzhou | 0/10 (0) | 31/32 (96.9%) | / | 38/40 (95%) |
Total | 100/129 (77.5%) | 1085/1320 (82.2%) | 306/636 (48.1%) | 793/935 (84.8%) |
For detecting PRRSV antibody, 636 serum samples from pigs without vaccination against PRRSV were detected by ELISA, and the average positive rate of PRRSV-specific antibody was 48.1% (Table 1). PRRSV appeared in the six regions of Hunan province, and the highest positive rate was 94.3% in Yiyang, whereas the lowest was 37.4% in Changde (Table 1). The seropositivity of PRRSV between the sample locations (n = 6) was also statistically significant by using chi-square test (χ2 = 54.095, df = 5, p < 0.001). Moreover, the highest positive rate in different growth stages was 77.8% for boars, and the lowest was 18.9% for fattening pigs (Fig. 2B). Unlike CSFV, PRRSV antibody in piglets first increased from one week old to two weeks old, and then decreased gradually with increase of piglets' age (Fig. 2B).
Seroprevalence-specific rates of immunized pigs.
Vaccination efficacies against CSFV has been studied in Hunan province, and the positive rates of CSFV antibody was 82.2% by detecting 1320 serum samples in Hunan province (Table 1). By analysis of regional differences, the vaccination efficacy in Yongzhou was best with the sera-positive rate is 96.9%, but the positive rates of four regions (Changsha, Shaoyang, Changde, and Chenzhou) were below the average (Table 1). Further statistical analysis, the seropositivity of CSFV between the sample locations (n = 8) was statistically significant by using chi-square test (χ2 = 17.074, df = 7, p = 0.017). The vaccination efficacy was not uniform at different growth stages, the positive rate from high to low was boars (92.6%), sows (90%), piglets (75.9%), fattening pigs (69.3%), and nursery pigs (50.3%) (Table 2).
Table 2
Positive rate of CSFV antibody in immune pigs of different growth stage
Growth stage | No. of tested samples | No. of positive samples | Positive rate |
Piglets | 54 | 41 | 75.9% |
Nursery pigs | 145 | 73 | 50.3% |
Fattening pigs | 192 | 133 | 69.3% |
Sows | 835 | 751 | 90% |
Boars | 94 | 87 | 92.6% |
Total | 1320 | 1085 | 82.2% |
Vaccination efficacies against PRRSV were also studied in Hunan province, the positive rate of PRRSV antibody in sera was 84.4% by detecting 935 serum samples (Table 1). About the regional difference, the highest positive rate was 95.8% in Yiyang with the best vaccination efficacy, and the lowest was 74% in Hengyang (Table 1). The seropositivity of PRRSV between the sample locations (n = 8) was also significantly different using chi-square test (χ2 = 20.309, df = 7, p = 0.005). Among various growth stages, the positive rate of sows was highest (88.1%) implying that the vaccination efficacy reached a high level, the lowest rate was 28.6% in piglets, which indicated a poor vaccination efficacy (Table 3).
Table 3
Positive rate of PRRSV antibody in immune pigs of different growth stage
Growth stage | No. of tested samples | No. of positive samples | Positive rate |
Piglets | 14 | 4 | 28.6% |
Nursery pigs | 48 | 29 | 60.4% |
Fattening pigs | 68 | 56 | 82.4% |
Sows | 720 | 634 | 88.1% |
Boars | 85 | 70 | 82.4% |
Total | 935 | 793 | 84.8% |