Field Efficacy of New PRRS Vaccine Against Local Thai PRRS Strain

Porcine Reproductive and Respiratory Syndrome (PRRSV) was first isolated in Thailand in 1996 from suckling and nursery pigs. A modified live PRRSV vaccine is an efficient and effective tool to decrease the mortality rate and increase nursery and growing-finishing pig performance. The PRRSV modified live virus vaccine belonging to the US genotype was registered and its use became common practice in Thai commercial swine herds in 2007. The objective of this field study was to compare the efficacy of two commercial PRRS vaccines, the Ingelvac PRRS® MLV vaccine and the Fostera PRRS® vaccine, in nursery pigs against local PRRS strain in Thailand.

A total of 40 piglets from four parity sows were randomized by size and weight, were divided into two groups, T01 and T02 with 20 piglets each. Both groups were vaccinated at 2 weeks of age. T01 pigs were injected with the Ingelvac PRRS® MLV while the T02 pigs were vaccinated with the Fostera PRRS®. Blood samples were collected on days 0, 28, 57 and 98 post-vaccination. Moreover, the blood samples were kept in plain tubes and allowed to clot at room temperature. After that, the sera were separated and stored at ≤ -20 °C until analysis. All samples were checked for PRRSV antigen in the serum and ELISA titer using the Reverse Transcription Polymerase Chain Reaction (RT-PCR) and IDEEX PRRS 3X ELISA Antibody tests, respectively.

All pigs in group T01 were found to have negative PRRSv antigen results on days 0, 28 and 98, respectively, these results were similar to the pigs in group T02. In addition, group T01 showed twelve of twenty samples positive (60%), while group T02 had only two of seventeen samples showing a positive result (11.8%) on day 57. In addition, pigs in group T01 had mean s/p ratios of; 2.359, 1.672, 1.0975 and 1.887 on days 0, 28, 57 and 98, respectively. Group T02 showed mean s/p ratios of; 1.799, 0.941, 0.762 and 1.017 on days 0, 28, 57 and 98, respectively. On day 28 post vaccination, three pigs in group T02 were sero-negative (negative is an s/p ratio < 0.4). However, some pigs in both groups were found to have a sero-negative result; three pigs in group T01 and five pigs in group T02 on day 57. On the last blood collection day, group T01 did not have a sero-negative result, while group T02 did show a sero-negative result for three samples.

PRRS vaccination was effective at reducing viremia, which the RT-PCR found that all pigs were negative at Day 0, and the mean serum s/p ratio of anti-PRRS antibody titers were high. In conclusion, the Fostera PRRS® vaccine had a more positive effect on reducing the viremia than the Ingelvac PRRS® MLV vaccine.

Disclosure of Interest: None Declared.