A porcine animal or a porcine cell comprising at least one modified chromosomal sequence in a gene encoding a CD163 protein, wherein the modification reduces the susceptibility of the animal, or cell to infection by a porcine reproductive and respiratory syndrome virus (PRRSV), as compared to the susceptibility of an animal or cell that does not comprise a modified chromosomal sequence in a gene encoding a CD163 protein to infection by PRRSV and wherein the modified chromosomal sequence comprises a modification selected from the group consisting of: a 2 base pair insertion between nucleotides 3,149 and 3,150 as compared to reference sequence SEQ ID NO: 47, with a 377 base pair deletion from nucleotide 2,573 to nucleotide 2,949 as compared to reference sequence SEQ ID NO: 47 on the same allele; a 1506 base pair deletion from nucleotide 1,525 to nucleotide 3,030 as compared to reference sequence SEQ ID NO: 47; a 7 base pair insertion between nucleotide 3,148 and nucleotide 3,149 as compared to reference sequence SEQ ID NO: 47; a 1280 base pair deletion from nucleotide 2,818 to nucleotide 4,097 as compared to reference sequence SEQ ID NO: 47; a 1373 base pair deletion from nucleotide 2,724 to nucleotide 4,096 as compared to reference sequence SEQ ID NO: 47; a 1467 base pair deletion from nucleotide 2,431 to nucleotide 3,897 as compared to reference sequence SEQ ID NO: 47; a 28 base pair deletion from nucleotide 3,145 to nucleotide 3,172 as compared to reference sequence SEQ ID NO: 47; a 1387 base pair deletion from nucleotide 3,145 to nucleotide 4,531 as compared to reference sequence SEQ ID NO: 47; a 1382 base pair deletion from nucleotide 3,113 to nucleotide 4,494 as compared to reference sequence SEQ ID NO: 47, wherein the deleted sequence is replaced with an 11 base pair insertion beginning at nucleotide 3,113; a 1720 base pair deletion from nucleotide 2,440 to nucleotide 4,160 as compared to reference sequence SEQ ID NO: 47; and a 452 base pair deletion from nucleotide 3,015 to nucleotide 3,466 as compared to reference sequence SEQ ID NO: 47. a 2 base pair insertion between nucleotides 3,149 and 3,150 as compared to reference sequence SEQ ID NO: 47, with a 377 base pair deletion from nucleotide 2,573 to nucleotide 2,949 as compared to reference sequence SEQ ID NO: 47 on the same allele; a 1506 base pair deletion from nucleotide 1,525 to nucleotide 3,030 as compared to reference sequence SEQ ID NO: 47; a 7 base pair insertion between nucleotide 3,148 and nucleotide 3,149 as compared to reference sequence SEQ ID NO: 47; a 1280 base pair deletion from nucleotide 2,818 to nucleotide 4,097 as compared to reference sequence SEQ ID NO: 47; a 1373 base pair deletion from nucleotide 2,724 to nucleotide 4,096 as compared to reference sequence SEQ ID NO: 47; a 1467 base pair deletion from nucleotide 2,431 to nucleotide 3,897 as compared to reference sequence SEQ ID NO: 47; a 28 base pair deletion from nucleotide 3,145 to nucleotide 3,172 as compared to reference sequence SEQ ID NO: 47; a 1387 base pair deletion from nucleotide 3,145 to nucleotide 4,531 as compared to reference sequence SEQ ID NO: 47; a 1382 base pair deletion from nucleotide 3,113 to nucleotide 4,494 as compared to reference sequence SEQ ID NO: 47, wherein the deleted sequence is replaced with an 11 base pair insertion beginning at nucleotide 3,113; a 1720 base pair deletion from nucleotide 2,440 to nucleotide 4,160 as compared to reference sequence SEQ ID NO: 47; and a 452 base pair deletion from nucleotide 3,015 to nucleotide 3,466 as compared to reference sequence SEQ ID NO: 47.