Seroprevalence rates in unvaccinated pigs.
A total of 129 unvaccinated pigs from eight regions were sampled for CSFV antibody testing, and 77.5% (100/129) were positive for CSFV (Table 1). Furthermore, the Chenzhou and Yueyang regions showed the minimum and maximum positive rates for CSFV, i.e., 0 (0/10) and 100% (4/4), respectively, and the rate of CSFV seropositivity showed a significant difference among the sample locations (n=8) according to the chi-square test (χ2 = 43.648, df = 7, p < 0.001). The results showed no CSFV infection in fattening pigs (0/10); all the positive CSFV samples were from the piglets (100/100). It is worth noting that the CSFV antibody level in piglets decreased gradually with increasing piglet age (Fig. 2A).
For detecting PRRSV antibody, 636 serum samples from pigs not vaccinated against PRRSV were examined by ELISA, and the average rate of PRRSV-specific antibody positivity was 48.1% (Table 1). PRRSV appeared in the six regions of Hunan Province, the highest positive rate was 94.3% in Yiyang, whereas the lowest was 37.4% in Changde (Table 1). The rate of PRRSV seropositivity showed a significant difference among the sample locations (n=6) according to the chi-square test (χ2 = 54.095, df = 5, p < 0.001). Moreover, the highest positive rate among the different growth stages was 77.8% in boars, and the lowest was 18.9% in fattening pigs (Fig. 2B). Unlike for CSFV, the PRRSV antibody level in piglets first increased from one week old to two weeks old and then decreased gradually with increasing piglet age (Fig. 2B).
Seroprevalence rates in immunized pigs.
The efficacy of vaccination against CSFV was studied in Hunan Province, and the rate of CSFV antibody positivity was determined to be 82.2% by analysing 1320 serum samples from Hunan Province (Table 1). Analysing regional differences showed that the vaccination efficacy was the best in Yongzhou, with a seropositivity rate of 96.9%, while the positivity rates in four regions (Changsha, Shaoyang, Changde, and Chenzhou) were below the average (Table 1). On further statistical analysis, the rate of CSFV seropositivity showed a significant difference among the sample locations (n=8) according to the chi-square test (χ2 = 17.074, df = 7, p = 0.017). The vaccination efficacy was not uniform at different growth stages, and the highest to lowest positivity rates were as follows: boars (92.6%), sows (90%), piglets (75.9%), fattening pigs (69.3%), and nursery pigs (50.3%) (Table 2).
The seroprevalence of PRRSV-specific antibodies in immunized pigs was also studied in Hunan Province, and the rate of PRRSV antibody positivity in sera was found to be 84.4% by analysing 935 serum samples (Table 1). Regarding regional differences, the highest positivity rate was 95.8% in Yiyang, and the lowest was 74% in Hengyang (Table 1). The rate of PRRSV seropositivity showed a significant difference among the sample locations (n=8) according to the chi-square test (χ2 = 20.309, df = 7, p = 0.005). Among the various growth stages, sows showed the highest seropositivity rate (88.1%), while piglet showed the lowest (28.6%) (Table 3).