Delayed type hypersensitivity response to PCV2 antigen in pigs born from unvaccinated or Circovac-vaccinated sows under Italian field conditions

none6siDelayed-type hypersensitivity (DTH) is revealing cellular mediated immunity towards an antigen and can be adapted for vaccine compliance tests. This study aimed to confirm this potential for PCV2 vaccination under Italian field conditions. First farm: thirty three-week-old just-weaned piglets born from unvaccinated sows were either vaccinated (n=15) with CIRCOVAC IM 0.5mL or left unvaccinated (n=15). Five weeks later, the pigs were intradermally inoculated with 0.1-0.2mL of CIRCOVAC antigen solution in the lower abdomen area. The diameter of skin reaction (erythema) at the point of inoculation was visually inspected 24h post-inoculation. Second farm: 30 five-week-old piglets born from CIRCOVAC-routinely-vaccinated sows were either vaccinated with CIRCOVAC or left unvaccinated. The DTH reaction was analogously assessed, both before vaccination and 5 weeks post-vaccination. Piglets born from vaccinated sows were bled at weaning and all experimental animals at 5 weeks post-vaccination . Antibodies were titrated using an in-house ELISA or a seroneutralization technique. First farm: only 33% of vaccinated piglets showed high anti-PCV2 ELISA titres following vaccination. Vaccinated pigs exhibited consistent and significantly higher seroneutralizing titres than unvaccinated pigs indicating a proper vaccine take. The proportion of pigs showing erythema (100% vs. 33%) and the average diameter (25±15 mm vs. 4±7 mm) was significantly higher (p<0.01) for the vaccinated animals. Second farm: piglets born from vaccinated sows consistently displayed high ELISA titres and a mild reaction (9±4mm) to the DTH test before vaccination. Five weeks later, ELISA titres were significantly decreased (p<0.01) in unvaccinated pigs compared to vaccinated ones. The diameter of the skin reaction strongly increased (p