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• Pigs vaccinated at 1 day of age with Suvaxyn^® PRRS MLV had less viremia and nasal shedding than unvaccinated pigs following challenge on day 28 with a virulent field strain of porcine reproductive and respiratory syndrome virus (PRRSV-1).
• Study results confirm ability of Suvaxyn PRRS MLV to provide protection prior to weaning when given to day-old piglets in the presence of maternal passive immunity.
• Reducing viremia and shedding in weaned piglets is critical to curbing the spread of virulent PRRSV-1 field strains and associated mortalities and performance losses.

PRRSV causes reproductive disease in sows and is also associated with respiratory problems, secondary infections and reduced performance in growers and finishers. Mortality varies but can be extremely high in some cases.^2,3 New, highly pathogenic strains of the virus such as AUT15-33 present a significant threat to the swine industry, with the effects of PRRSV already costing European producers approximately €1.5 billion per year.⁴ Researchers from Zoetis and the University of Veterinary Medicine, Vienna, therefore conducted a study to evaluate the ability of Suvaxyn^® PRRS MLV to reduce viremia and viral shedding following experimental infection with PRRSV-1 AUT15-33.

Study design and results

In the study, 21 piglets were intramuscularly vaccinated with Suvaxyn PRRS MLV at 1 day of age according to label instructions, while 20 piglets were sham-treated and served as unvaccinated controls. At 28 days of age, all piglets were challenged intranasally with PRRSV-1 AUT15-33. After weaning, the vaccinated and unvaccinated pigs were commingled and observed for 2 weeks. Serum, nasal and oral swabs were collected every 2 to 3 days and analyzed by real-time quantitative polymerase chain reaction.

Serum and nasal swabs from the vaccinated piglets had significantly (p < 0.05) lower loads of PRRSV RNA than those from unvaccinated piglets on most sampling days (Figures 1 and 2). All of the unvaccinated piglets were viremic and had virus in nasal swabs, whereas only 71.4% of the vaccinated animals were viremic and 38.1% shed virus.

In addition, the percentage of days with viremia in the group of vaccinated pigs was 19.6% compared to 55.1% for the unvaccinated animals.

Reduced viremia and shedding cuts risk to herds

“Reducing viremia and shedding through vaccination is critical to curbing the spread of PRRSV-1 field strains among weaned piglets and limiting related losses,” explained Marta Cabana, DVM, PhD, a research and development scientist at Zoetis and principal investigator of the study.

“This work confirms the ability of Suvaxyn PRRS MLV to provide protection against virulent PRRSV-1 field strains, including AUT15-33, by weaning when administered at 1 day of age,” she added, noting that Suvaxyn PRRS MLV is the only commercial PRRSV-1 vaccine in the EU authorized for use in day-old pigs.

“Being able to vaccinate on day 1 helps close the gap in immunity between the loss of maternal antibodies around 3 to 4 weeks of age and the onset of vaccine immunity, ensuring pigs are protected from before weaning through slaughter.”⁵