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Abstract
The aim of this study was to understand the
pathogenesis of PRRS virus. Three groups of 3-, 21-, and
28-day-old specific pathogen free pigs were inoculated
intranasally with 105 TCID50 PRRS virus. The 3-day-old
group was sacrificed 3 days later. The 21- and 28-day-old
pigs were sacrificed 10 days later. The clinical signs, gross
and histopathological lesions were observed. The effect of
PRRS virus on the macrophages of various organs, including
monocytes, lung macrophages, Kupffer's cells, spleen
reticular cells, mesangial cells, microglia cells, Peyer's
patch and macrophages in the lung lymph node, were
examined detailedly by electron microscopy. Besides, virus
isolation and immunostaining were performed to prove that
the inoculations were successful. Bacterial contamination
was ruled out by bacterial isolation. In order to understand
whether the PRRS virus can exacerbate secondary infection,
pseudorabies virus and Salmonella cholerasuis were
inoculated after PRRS virus infection and the clinical signs
and pathological lesions were observed.
The results showed that the pigs did not show anorexia,
depression, tachypnea and abdominal respiration after PRRS
virus inoculation. Two 21-day-old pigs developed
polyserositis, and mild consolidation was observed in other
pigs' lungs. Hemorrhage was observed in the lung lymph node
of 21- and 28-day-old pigs. No visible gross lesion was found
in the viscera of 3-day-old pigs. In histopathologic
examination, it was observed in all inoculated pigs that the
alveolar wall was thickened and the lung parenchyma was
infiltrated by lymphocytes. Peripheral hemorrhage in lung
lymph node was found in 21- and 28-day-old pigs. In the pigs
which got polyserositis, the serosa of various organs,
including heart, liver, spleen, lung, intestine and adrenal
gland, were infiltrated by lymphocytes and neutrophils. Two
3-day-old pigs had focal hemorrhage in the epicardium and
urinary bladder respectively. Ultrastructural examination of
the thickened alveolar wall revealed that most cells were
endothelial cells, blood cells, fibroblasts and type II
pneumocytes.
In experiments of dual infection, no difference in the
morbidity, mortality and histopathological lesion was seen
between salmonella-inoculated and salmonella-PRRSV co-
infected pigs. The result indicated that PRRS virus did not
exacerbate the secondary infection of salmonella. However,
dual infection of PRRS virus and pseudorabies virus showed
higher morbidity and more severe histopathological lesion.
According to the results, it could be concluded that
PRRS virus only caused a mild effect on pig's lymphatic
tissues except peripheral hemorrhage was observed in the
lung lymph node. However, PRRS virus did exacerbate the
secondary infection of pseudorabies virus, but didn't
exacerbate the secondary infection of salmonella. Therefore,
it is worth to pay attention about the viral secondary infection
in PRRS virus infected pigs.
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