VIRAEMIA AND SEROCONVERSION IN PIGLETS FOLLOWING VACCINATION WITH PRRSV-EU TYPE VACCINE - A FIELD OBSERVATION

摘要

One of the methods for controlling porcine reproductive and respiratory syndrome (PRRS) is to use modified live vaccines (MLV's). This report presents field observations on the profiles of seroconversion obtained by ELISA, and viraemia measured by RT-PCR, in piglets vaccinated with Porcilis PRRS (Intervet) in a farrow-to-finish herd with 400 sows where a Polish wild type PRRSV strain has circulated since 2001. In February 2003, a vaccination program started involving immunization of sows every 6 months and of piglets at around 40 d of age. Twelve piglets were ear-tagged at 14 d and bled every 2-3 weeks until 132 d of life. The majority of piglets had detectable maternal antibodies against PRRSV at day 14. As maternal antibodies waned, most (10 of 11) pigs were seronegative at the time of vaccination. However, one pig, which had the highest levels of maternal antibodies, remained positive (S/P >= 0.5) until day 43. After vaccination at 41 d of age, most of the pigs seroconverted between 21 and 42 dpost-vaccination (dpv). One pig did not seroconvert until the end of the study. Viraemia was not detected by PCR until 2 dpv, when vaccine virus was identified by nucleotide sequencing. Porcilis viraemia was detected intermittently up to 42 dpv. At 68 and 92 dpv viraemia caused by the wild type strain was detected in some animals. In summary, it can be concluded that vaccination program protected pigs up to 108 d of life against the infection with the local virulent strain. Yet, our findings of viraemiawith Polish field virus in vaccinated pigs also indicate that the high levels of sequence divergence between the Porcilis PRRS modified live vaccine and Polish field strains may reduce vaccine efficacy.