Porcine reproductive and respiratory syndrome virus (PRRSV) is costing farmers millions of dollars each year. Upon infection, farmers need to cull their herds due to slowed growth and reproductive issues. Although there is a vaccine available, it is not an ideal solution for this particular disease. The vaccine will not eradicate the virus, only lesson the impact of the disease on farms. Scientists are trying to determine the transmission of the disease, in order to solve the problem. A transmembrane protein CD169 has been identified as a receptor for PRRSV, and was thought to be a required gene for the virus to propagate. In a study conducted by Kansas State University and University of Missouri this theory was disproved. The scientists removed the CD169 gene, and found that the genetically modified pigs were still susceptible to the disease. 

The pigs were genetically modified to not express the CD169 protein by altering cells from fetal fibroblast cell lines of white pigs. If the receptor protein was removed, they hypothesized that the virus would be unable to infect the cells and the pig’s immune system could defend and kill the virus. To eliminate the protein, the scientists used homologous recombination as well as introduced premature stop codons in the DNA sequence of the gene to prevent expression of the protein. To see if the removal of the protein was successful, they used polymerase chain reaction (PCR), which is a method used to amplify DNA sequences. Once the scientists confirmed that the protein was missing, they infected pigs with the virus. After a period of time they tested the pigs for clinical signs of the disease including body conditions, respiratory signs and general activity. It was found that the absence of the CD169 gene did not affect PRRSV and the pigs still became sick with the disease. The discovery that the CD169 gene does not affect the virus will be useful information in determining the pathway for the virus, and will help determine the transmission that PRRSV takes.