Replication characteristics of eight virulent and two attenuated genotype 1 and 2 porcine reproductive and respiratory syndrome virus (PRRSV) strains in nasal mucosa explants

• PRRSV isolates were categorized based on viral shedding in nasal mucosa.
• PRRSV isolates were categorized based on the number of infected cells in nasal mucosa.
• Attenuated PRRSV strains showed a limited number of replication cycles.
• Two different patterns of infection were observed between type 1 and type 2 PRRSV strains.

Porcine reproductive and respiratory syndrome virus (PRRSV) can spread in between pigs via contact and airborne route. It was shown before that the highly pathogenic PRRSV strain Lena was able to replicate 10–100 times more in the nasal mucosa compared to the low pathogenic PRRSV strain LV. In this work, the replication characteristics of four type 1 (LV, 07V063, 08VA, 13V091), three type 2 (VR2332, MN-184, VN) and two attenuated (MLV-DV, MLV-VR2332) PRRSV strains were studied. After 72 hpi, mean virus titers reached 104.5–4.8 TCID50/ml for LV and 08VA, 105.2–5.4 TCID50/ml for VR2332 and Lena, and 105.8–6.3 TCID50/ml for 07V063, 13V091, MN-184 and VN strains, whereas attenuated strains remained below detection limit. The mean number of PRRSV-positive cells/mm2 at 72 hpi was 1.1 and 1.3 for the attenuated strains and LV, 13.3 for 08VA, 23.5 and 29.3 for VR2332 and 07063, 31.1 and 33.8 for 13V091 and Lena, and, 39.1 and 59.2 for MN-184 and VN respectively. All the LV and MLV-LV infected cells were Sn+, whereas all other strains also infected Sn− macrophages. In conclusion, (i) based on the virus shedding in the respiratory explants, PRRSV strains can be categorized as poor (MLV-DV, MLV-VR2332, LV, 08VA), moderate (Lena, VR2332) and strong (07V063, 13V091, MN-184, VN) secretors, and (ii) based on the number of infected cells isolates can be categorized as low (MLV-DV, MLV-VR2332, LV), moderately (08VA, VR2332), highly (07V063, Lena, 13V091) and hyper (MN-184, VN) virulent in the nasal mucosa.