The purpose of this study was to assess the pathogenicity of a strain of PRRSV and in addition to test a commercial available PRRS-vaccine (Porcilis® PRRS) before infection with a challenge virus.
Through the outcome a new challenge model will be created for further experimental investigations.
The main investigated parameters in this study were respiratory signs and pathologic lesions in the lungs after the infection with PRRSV.
The challenge began on day -7 and lasted for 64 days. A total of 36, 3-week-old PRRSV-free piglets were allocated randomly into a control group, an infected group (inf-group) and a vaccinated/infected group (vac/inf-group). On day 0 vac/inf-piglets (n =12) were intramuscularly (Porcilis® PRRS) vaccinated and 35 days later the inf- (n = 12) and vac/inf-group (n = 12) were intranasally and intramuscularly challenged with a PRRSV-EU strain. The control group (n = 12) was kept as a non-vaccinated and non-challenged control group. They only received a physiological saline solution on the infection date.
Throughout the study the animals were clinically observed daily, whereby mainly dyspnoea, cough, eye and nasal discharge, behaviour, appetite and rectal temperature were examined. All three groups were weighed on fixed dates (-7, 0, 16, 35, 39, 44, 50, 56) and 18 animals each were necropsied on two different dates (day 44/45, day 56/57).
Significant differences were detected between the control and infected animals. There were differences in rectal temperature and daily weight gain. The macroscopic pathologic observation of the lungs showed that 10 of 12 animals showed tan mottled areas and areas of firm consistency in the lungs at the first and second necropsy. Some lungs were affected up to 100%. The vac/inf-group showed only macroscopic changes at the first observation date. Moreover, the histological lesions (pneumotic hypertrophy and hyperplasia, septal infiltration with mononuclear cells, necrotic debris, intraalveolar accumulation with inflammation cells, perivascular accumulation with inflammation cells) showed a reduction in all groups from the first to the second necropsy date. The vac/inf-group featured 37 % and the inf-group 33 % reduction of the histologic lungs lesions.
There were significant differences in "pneumotic hypertrophy and hyperplasia", "septal infiltration with mononuclear cells", "intraalveolar accumulation with inflammation cells" and "perivascular accumulation with inflammation cells" between the control and inf- as well as the vac/inf-animals. The histological lesion "necrotic debris" showed significant differences only between the control and infected animals.
This study demonstrated that this challenge virus is able to induce an infection because there were significant differences between the control and the inf- as well as the vac/inf-group. Therefore this virus can be used for further investigations. The vac/inf-group showed better daily weight gains and lesser lung lesions than the merely infected ones.
Nevertheless, no significant differences in the whole study could be demonstrated in any parameter between the inf- and vac/inf-piglets.