Clin Vaccine Immunol. 2007 Jan 10; Protection Against Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) Infection through Passive Transfer of PRRSV-Neutralizing Antibodies is Dose-dependent. Lopez OJ, Oliveira MF, Alvarez Garcia E, Kwon BJ, Doster A, Osorio FA.
Previous work in our laboratory demonstrated that passive transfer of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV)-neutralizing antibodies (NA) protected pregnant sows against reproductive failure and conferred sterilizing immunity in sows and offspring. Herein, we report on the dose requirement for protection by passive transfer with NA in young weaned pigs.
Presence of a 1:8 titer of PRRSV-NA in serum consistently protected pigs against viremia. Nevertheless, their lungs, tonsils, buffy-coat cells and peripheral lymph-nodes contained replicating PRRSV similar to the infected control group. Likewise, these animals excreted infectious virus to sentinels similar to the infectivity control animals.
In an attempt to reach complete protective immunity equivalent to that previously observed in sows, the pigs were transferred with a higher titer of PRRSV-NA (level 1:32), and even then apparent sterilizing immunity was attained in only 50% of the animals.
In conclusion, the presence of anti-PRRSV NA in serum with a titer of 1:8 is enough to block viremia but not peripheral tissue seeding and transmission to contact animals. While a relatively low level of NA in blood is capable of conferring sterilizing immunity against PRRSV in sows, the amount of NA necessary to obtain full protection of a young weaned pig would be significantly higher, suggesting that differences exist in the PRRSV pathogenesis between both age groups.
In addition, the titer of NA could be a helpful parameter of protection in the assessment of PRRSV vaccines.