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Is the intradermal vaccination against PRRS as efficacious as the intramuscular one??

25 November 2020, at 9:00am

The advantages of the intradermal (ID) administration by a needle-less device are that it is less invasive, painless, safe, quick and easy. Furthermore, the ID administration could induce a stronger cellular response compared to the intramuscular (IM) due to the delivery through the ID route could induce T cell polarization favoring the induction of interferon gamma secreting cells (IFN-γ-SC). In PRRSV infection, interleukin 10 (IL-10) levels are reportedly associated with severity of clinical disease (van Reeth and Nauwynck, 2000) and can delay the immune response. Higher IFN-γ-SC in ID vaccinated pigs could be due to the lower IL-10 levels.

The objectives of the present study were to investigate the immune response and clinical protection of pigs vaccinated IM or ID with UNISTRAIN® PRRS (Laboratorios HIPRA) against challenge with HP-PRRSV2 (Thai strain) and coinfection with PRRSV1. Moreover, the second objective of this study was to learn more about safety of the vaccine by evaluation of IL-10 production as it can delay the immune response (Madapong et al., 2020).

Material and methods:

Forty-two, 3-week-old, PRRSV-free pigs were allocated into 7 groups as shown in Table 1. Following vaccination and challenge at 35 days post vaccination, pigs were monitored for PRRSV quantification by RT-qPCR, safety of the vaccine by IL-10, immune response including ELISA and IFN-γ-PC and macroscopic lung lesions.

Table 1: Groups distribution during the entire study
Table 1: Groups distribution during the entire study

Results

Following vaccination, there was no difference in antibody response among vaccinated groups. ID-vaccinated pigs had shorter viremic phase and lower RNA level compared to IM-vaccinated pigs. ID-vaccinated pigs had significant lower IL-10 levels (figure 2), and significant higher IFN-g-SC compared to IM-vaccinated pigs (figure 3). Following challenge, ID-vaccinated pigs had significantly lower PRRSV RNA and lung lesion compared to IM-vaccinated pigs at 7 days post challenge (DPC) (figure 4 and 5).

Figure 2. Quantification of IL-10 in the supernatant of stimulated PBMC with the vaccine strain following vaccination.
Figure 2. Quantification of IL-10 in the supernatant of stimulated PBMC with the vaccine strain following vaccination.
Figure 3. Evaluation of PRRSV-specific IFN- γ -secreting cells (SC) after stimulation with (A) homologous virus (vaccine virus), (B) heterologous PRRSV1 (AN06EU4204) and (C) heterologous HP-PRRSV2 (FDT10US23). Values are expressed as the mean±SEM.
Figure 3. Evaluation of PRRSV-specific IFN- γ -secreting cells (SC) after stimulation with (A) homologous virus (vaccine virus), (B) heterologous PRRSV1 (AN06EU4204) and (C) heterologous HP-PRRSV2 (FDT10US23). Values are expressed as the mean±SEM.
Figure 4. Microscopic lung lesions following challenge of the (A) non vaccinated/challenged, (B) IM vaccinated pigs, (C) ID vaccinated pigs and (D) non vaccinated/non challenge pigs. H&E staining. Bar =100 μm.
Figure 4. Microscopic lung lesions following challenge of the (A) non vaccinated/challenged, (B) IM vaccinated pigs, (C) ID vaccinated pigs and (D) non vaccinated/non challenge pigs. H&E staining. Bar =100 μm.
Figure 5. Macroscopic lung lesions following challenge at 7 DPC of the (A) non vaccinated/challenged, (B) IM vaccinated pigs, (C) ID vaccinated pigs and (D) non vaccinated/non challenge pigs.
Figure 5. Macroscopic lung lesions following challenge at 7 DPC of the (A) non vaccinated/challenged, (B) IM vaccinated pigs, (C) ID vaccinated pigs and (D) non vaccinated/non challenge pigs.

Conclusions

The results of the study suggested that:

  • Vaccination with UNISTRAIN® PRRS, either by IM or ID, can induce humoral and cell-mediated immune responses.
  • UNISTRAIN® PRRS administered by either IM or ID can provide heterologous protection against challenge with HP-PRRSV-2, either alone or in coinfection with PRRSV-1, as demonstrated by reduced lung lesions and viremia.
  • IL-10 production was delayed and lower in ID vaccinated pigs.

In conclusion, the ID route might represent an alternative to improve vaccine efficacy, as it induced lower IL-10 levels and more IFN-γ-SC.