PRRSV challenge in vaccinated pigs

In PRRS challenge studies a large amount of data is available and is often presented in tables to demonstrate the effect of challenge. All of the effects of challenge are happening in the pigs at the same time. Still it is a challenge to visualize the simultaneous events in an optimal way. This paper aims to visualize a number of simultaneous effects of PRRSV challenge in vaccinated pigs using a time spatial moving graph.

Three blinded, vaccination-challenge efficacy studies were performed using separate cohorts of pigs (n=56 per study) to evaluate duration of immunity conferred by a new European-derived, PRRSV modified live virus (MLV) vaccine (Ingelvac PRRSFLEX EU). Pigs received either vaccine (Group 1), or placebo (Groups 2 and 3). Groups 1 and 2 were subsequently challenged with heterologous European PRRSV isolate 205817 at 20, 24 or 26 weeks post-vaccination. Group 3 was the negative challenge control. Percentage of viremic pigs, viral load in blood and rectal temperature were measured daily from day of challenge until the end of study 10 days later. Primary endpoints were gross and histological lung lesion scoring and viral load in lung tissue 10 days following PRRSV challenge. Secondary endpoints included clinical observations and average daily weight gain.

Significantly lower mean histological lung lesion scores were observed in Group 1 versus Group 2 at 20 (p=0.0065), 24 and 26 weeks (p< 0.0001). Mean viral load in lung tissue was significantly lower in Group 1 versus Group 2 (p=< 0.0001) at each observation. Cumulative viral loads in serum during days 1–10 post-challenge were significantly lower in Group 1 than in Group 2 (p=< 0.0001) in all studies. A significant increase in average daily weight gain was observed in Group 1 compared with Group 2 at 20 weeks (p=0.0027) and 24 weeks (p=0.0004), but not at 26 weeks (p=0.1041).Simultaneous rectal temperature, blood viral loads, % of viremic pigs, and the end point histological lung lesions over 10 days post challenge, can be demonstrated using a time spatial moving graph.

These studies demonstrate duration of immunity was maintained for up to 26 weeks after PRRSV vaccination. This was confirmed by reduced gross and histological lung lesion in all studies, as well as reduced viral loads and a significantly lower number of viremic animals after artificial challenge. All improved parameters due to PRRSV MLV vaccination were effectively explained by using alternative visualisation tools.

Disclosure of Interest: None Declared.