Evaluation of immunoprotection of SD-R against homologous and
heterologous strains
Twenty-six 28-day-old PRRSV-free piglets were obtained from two
PRRS-free farms in Harbin. Thirteen PRRSV-free piglets used to assess
homologous protection were randomly divided into three groups (A1-C1).
Other PRRSV-free piglets used to test heterologous protection were
randomly divided into three groups (A2-C2). Five piglets for each group
were used for immunization and inoculation (A1, B1, A2 and B2), except
for three piglets in negative control groups C1 and C2. Piglets in
groups B1 and B2 were inoculated intramuscularly with
105.0TCID50 SD-R. After 28 days
post-vaccination (dpv), piglets in groups A1, B1 and A2, B2 were
infected with 5th-passage SD
(4×105.0TCID50 per pig) and
5th-passage HLJWK108-1711
(4×105.0TCID50 per pig)
intramuscularly (2 ml) and intranasally (2 ml), respectively. The
animals were maintained in individual biosafety rooms. Clinical signs
and rectal temperatures were recorded daily. The body weights of the
piglets were measured weekly. Blood samples were periodically collected
from individual piglets and tested for viremia. All of the piglets were
euthanized at 21 dpi. Ten tissue samples were obtained from the hearts,
livers, spleens, lungs, kidneys, lymph nodes, tonsils, small intestines,
bladders, and stomachs for viral detection by
TaqMan®-based real-time fluorescence quantitative
RT–PCR (65).