Bartha-K61 vaccine protects nursery pigs against challenge with novel european and asian strains of suid herpesvirus 1

Abstract

The present study investigates the pathogenicity of two recently isolated strains of Suid herpesvirus 1 (SuHV1), the Greek strain Hercules and the Chinese strain HeN1, in unvaccinated pigs and in pigs vaccinated with a Bartha-K61 strain. In an experiment performed in negative pressure kiosks (isolators), 45-day old seronegative pigs previously oronasally /intramuscularly vaccinated with the Bartha-K61 vaccine strain, along with unvaccinated controls, were challenged either with the Hercules strain or the HeN1 strain of SuHV1. All animals were observed daily for clinical signs and body temperature and nasal swabs, faeces, blood and bodyweight were collected up to a maximum period of 20 days post-challenge (dpc). The results showed that, in the unvaccinated pigs, HeN1 strain was more virulent than the Hercules strain, with increased mortality, shorter time to death and higher group clinical score (p < 0.05). However, after vaccination with the Bartha-K61 vaccine, there was a drastic reduction in morbidity, mortality, bodyweight loss and virus excretion to almost a similar extent in both strains (p < 0.05). No significant differences were seen among the pigs of the two vaccinated groups compared to unvaccinated unchallenged controls, except a slight elevation in body temperature and in clinical score in the HeN1 vaccinees at 2 and 3 dpc, while bodyweight gain was similar to that of the negative control pigs. Our study showed that despite differences in virulence, the standard vaccination scheme with the Bartha-K61 strain could equally protect nursery pigs against both the European and Chinese strains.

Keywords: Aujeszky’s disease; Bartha-K61 vaccine; Pseudorabies; pig; variant.

Figure 1

Graphic display of the experimental study design including a timeline of vaccination, challenge, sampling (B-blood, NS-nasal, F-faecal swabs, BW-bodyweight) timepoints. Clinical signs and body temperature were recoded daily. Tissues (nasal mucosa, brain) were collected during pig death or final autopsy (doa = days of age; dpv = days post-vaccination; dpc = days post-challenge).

Figure 2

Clinical signs of unvaccinated or Bartha-K61 vaccinated pigs challenged with Hercules and HeN1 strains of SuHV1. A Rectal temperatures, B. Pig Daily Clinical Scores, C. Bodyweight increase. G1-Unvaccinated and unchallenged control pigs (green line; n = 4); G2-Unvaccinated and Hercules-challenged pigs (blue line; n = 5); G3-Unvaccinated and HeN1-challenged pigs (red line; n = 5); G4-Vaccinated and Hercules-challenged pigs (dashed violet line; n = 5); G5-Vaccinated and HeN1-challenged pigs (dashed orange line; n = 5). Different letters at the same day post-challenge show significant difference (p < 0.05).

Figure 3

Serology of unvaccinated or Bartha-K61 vaccinated pigs challenged with Hercules and HeN1 strains of SuHV1. A Serum neutralization (SN), B gB-ELISA titres, C. gE-ELISA titres. G1-Unvaccinated and unchallenged control pigs (green line; n = 4); G2-Unvaccinated and Hercules-challenged pigs (blue line; n = 5); G3-Unvaccinated and HeN1-challenged pigs (red line; n = 5); G4-Vaccinated and Hercules-challenged pigs (dashed violet line; n = 5); G5-Vaccinated and HeN1-challenged pigs (dashed orange line; n = 5). Different letters at the same day post-challenge show significant difference (p < 0.05).