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Research reported late last year challenged groups of pregnant sows with a virulent PRRS strain (NADC-8) at doses of either 100, 10,000 or 1 million tissue culture infectious doses (TCID₅₀). It found that each group of sows developed similar reproductive disease, with no differences in the clinical disease in the sows nor in fetal infection parameters.

The work demonstrates that only a minimal exposure dose is required to result in PRRSV induced reproductive disease. If a sow is exposed to sufficient virus to result in infection and viremia — which may occur with as little as one-to-10 infectious particles — then reproductive disease will ensue.

The good news is that the research also found that exposure dose has no significant impact on protection against reproductive disease in vaccinated animals. Groups of sows were vaccinated twice with a modified live PRRS vaccine (Ingelvac^® PRRS MLV), acclimated for 30 days, bred, and then challenged with either 100, 10,000 or 1 million TCID₅₀ PRRS virus (NADC-8) at 80 days of gestation. The researchers demonstrated that vaccination prevented fetal infection in 87 percent of the litters, with no significant difference between the challenge groups.

PRRS Virus

More on challenge dose

Effect of challenge dose and route on porcine reproductive and respiratory syndrome virus (PRRSV) infection in young swine. Yoon KJ, Zimmerman JJ, Chang CC, Cancel-Tirado S, Harmon KM, McGinley MJ. Vet Res 1999 Nov-Dec; 30(6):629-38.

To more information

The impact of exposure dose on PRRSV induced reproductive disease in vaccinated and unvaccinated sows. Yaeger, M. Proceedings of Swine Disease Conference for Swine Practitioners, Nov. 1999; 74-75.