A genetic marker allele conferring resistance to Ascaris suum in pigs

Mapping of quantitative trait loci (QTLs) has helped dissecting the genetics underlying the variation in resistance to helminth infections. In pigs, two single nucleotide polymorphisms (SNP TXNIP and SNP ARNT), both on chromosome 4, have been reported to be associated with Ascaris suum worm burden. In the present study we selected pigs with two SNP TXNIP genotypes (AA; N=24 and AB; N=24) which from eight weeks of age were experimentally infected with A. suum until necropsy at week 8 post first infection (p.i.) to test the hypothesis that pigs with the AA genotype would have lower worm burdens than pigs of the AB genotype. We used different indicators of resistance (worm burden, faecal egg counts, number of liver white spots and A. suum-specific serum IgG antibody levels) of which the first two traits were considered core traits and the last two traits were associated traits. Pigs of the AA genotype had lower mean macroscopic worm burden (2.4 vs. 19.3), lower mean total worm burden (26.5 vs. 70.1) and excreted fewer A. suum eggs at week 8 p.i. (mean number of eggs/g faeces: 238 vs. 1259) than pigs of the AB genotype. However, none of these differences were significant (P- values of 0.06, 0.06 and 0.14, respectively). In addition, pigs of the AA genotype had lower (though not significant) serum IgG antibody titres to three different A. suum antigens. There was no significant difference between genotypes in the number of liver white spots. The pigs were also genotyped at another locus (SNP ARNT) which showed a similar trend. The data presented here provide suggestive evidence that resistant pigs can be selected using a genetic marker, TXNIP, and that it is the B allele which is conferring susceptibility to A. suum infection. Our work confirmed that SNP ARNT is another diagnostic marker candidate for A. suum resistance and provides further support to the QTL on porcine chromosome 4 detected previously.