The assessment of efficacy of porcine reproductive respiratory syndrome virus inactivated vaccine based on the viral quantity and inactivation methods.

Kim H, Kim HK, Jung JH, Choi YJ, Kim J, Um CG, Hyun SB, Shin S, Lee B, Jang G, Kang BK, Moon HJ, Song DS.

Abstract

ABSTRACT:

BACKGROUND:

There have been many efforts to develop efficient vaccines for the control of porcine reproductive and respiratory syndrome virus (PRRSV). Although inactivated PRRSV vaccines are preferred for their safety, they are weak at inducing humoral immune responses and controlling field PRRSV infection, especially when heterologous viruses are involved.

RESULTS:

In all groups, the sample to positive (S/P) ratio of IDEXX ELISA and the virus neutralization (VN) titer remained negative until challenge. While viremia did not reduce in the vaccinated groups, the IDEXX-ELISA-specific immunoglobulin G increased more rapidly and to significantly greater levels 7 days after the challenge in all the vaccinated groups compared to the non-vaccinated groups (p < 0.05). VN titer was significantly different in the 106 PFU/mL PRRSV vaccine-inoculated and binary ethylenimine (BEI)-inactivated groups 22 days after challenge (p < 0.05). Consequently, the inactivated vaccines tested in this study provided weak memory responses with sequential challenge without any obvious active immune responses in the vaccinated pigs.

CONCLUSIONS:

The inactivated vaccine failed to show the humoral immunity, but it showed different immune response after the challenge compared to mock group. Although the 106 PFU/mL-vaccinated and BEI-inactivated groups showed significantly greater VN titers 22 days after challenge, all the groups were already negative for viremia.

Virol J. 2011 Jun 27;8(1):323. [Epub ahead of print]

Porcine reproductive and respiratory syndrome virus (PRRSV) influences infection dynamics of porcine circovirus type 2 (PCV2) subtypes PCV2a and PCV2b by prolonging PCV2 viremia and shedding.

Abstract

The objective of this study was to determine the effect of porcine reproductive and respiratory syndrome virus (PRRSV) infection on porcine circovirus type 2 (PCV2) subtypes a (PCV2a) or b (PCV2b) viremia and shedding characteristics in oral, nasal and fecal samples in experimentally infected pigs. Twenty-three, 2- to 6-week-old pigs were randomly divided into five groups: negative control (n=3), PCV2a-I (n=5), PCV2a-PRRSV-CoI (n=5), PCV2b-I (n=5), and PCV2b-PRRSV-CoI (n=5). Blood, oral, nasal and fecal swabs were collected in regular intervals from day post inoculation (dpi) 0 until dpi 70 and tested by quantitative real-time PCR for the presence and amount of PCV2 DNA and by ELISA for the presence of PCV2-specific antibodies. The results indicate that there were significantly (P<0.05) higher loads of PCV2a and PCV2b DNA in serum, oral swabs, nasal swabs and fecal swabs and a higher prevalence of detectable PCV2 antigen in tissues of pigs concurrently infected with PCV2 and PRRSV compared to pigs singularly infected with PCV2 further confirming that PRRSV enhances replication of PCV2. Moreover, PRRSV infection significantly prolonged the presence of PCV2 DNA in serum and increased the amount of PCV2 DNA in oral and nasal secretions and fecal excretions in the later stages of infection between dpi 28 and 70. Shedding patterns were similar between groups infected with PCV2a and PCV2b, indicating that there was no subtype-specific interaction with the PRRSV isolate used in this study. The results from this study highlight the interaction between PRRSV and PCV2 and the importance of controlling PRRSV infection in order to reduce PCV2 virus loads in pig populations.

Sinha A, Shen H G, Schalk S, Beach N M, Huang Y W, Meng X J, Halbur P G, Opriessnig T. Porcine reproductive and respiratory syndrome virus (PRRSV) influences infection dynamics of porcine circovirus type 2 (PCV2) subtypes PCV2a and PCV2b by prolonging PCV2 viremia and shedding. Veterinary microbiology 2011 [accepted].