Evaluation of a new commercially available PRRSV vaccine upon exposure to a recently isolated Belgian genotype 1, subtype 1 PRRSV strain (Flanders 13)

Recently a new live attenuated porcine reproductive and respiratory syndrome virus (PRRSV) vaccine became commercially available on the European market (Ingelvac PRRSFLEX EU, Boehringer Ingelheim). This vaccine is based on a genotype 1 subtype 1 strain. Subtype 1 strains cause reproductive disorders in breeders and limited respiratory problems in young pigs. In 2013, a more pathogenic genotype 1, subtype 1 strain was isolated from weaned pigs showing respiratory disorders on a Belgian farm (Flanders 13). In the present study, the degree of clinical and virological protection was assessed in pigs vaccinated with Ingelvac PRRSFLEX EU and challenged six weeks later with Flanders 13.

Twelve 4-weeks-old piglets from a PRRSV-negative farm were divided in 2 groups. Group Vac was vaccinated intramuscularly with Ingelvac PRRSFLEX EU and group Unvac was left unvaccinated. All piglets were challenged intranasally with PRRSV strain Flanders 13 (2 ml, 10⁵ TCID₅₀/dose) six weeks after (mock) vaccination. Blood was collected weekly during the experiment to follow the immune response (IPMA). After challenge, the animals were observed clinically for body temperature and respiratory disorders. Blood and nasal secretions were collected at challenge and at different days post challenge (dpc) in order to monitor viral replication and nasal shedding.

All vaccinated pigs seroconverted within two weeks after vaccination, whereas the control animals remained seronegative until challenge. Fever and other signs of disease were minimally observed in both groups upon challenge. After the peak viral load, a significant reduction in PRRSV titer was observed in the vaccinated group during the second week post challenge. The area under the curve (AUC) was significantly reduced in vaccinated animals compared to unvaccinated pigs, while the duration was slightly reduced. All pigs shed virus at 3 dpc with significantly lower PRRSV titers in nasal secretions in vaccinated group compared to unvaccinated controls. At 7 dpc, the mean PRRSV titer in vaccinated animals was also significantly lower. Vaccination shortened the duration of nasal shedding post challenge with 6.16 days and the mean virus titers in the nasal secretions (AUC) were significantly lower in vaccinated group compared to the unvaccinated group.

A sufficient protection was observed upon challenge with subtype 1 PRRSV strain Flanders 13 in pigs vaccinated with the new live attenuated vaccine Ingelvac PRRSFLEX EU. Viremia and nasal shedding of PRRSV Flanders 13 were significantly reduced (duration and viral titers) in vaccinated animals.

Disclosure of Interest: C. Bonckaert Conflict with: Boehringer Ingelheim paid for the study, C. Kraft: None Declared, G. Cluydts: None Declared, H. Nauwynck Conflict with: Boehringer Ingelheim paid for the study.