Detection of a quantitative trait locus associated with resistance to Ascaris suum infection in pigs

Helminths almost invariably have an over-dispersed distribution in the host population. Human and animal studies have provided evidence suggesting that a large part of this variation is due to host genetic factors. Recently, the heritability for roundworm (Ascaris suum) infection levels in pigs was estimated to be 0.45. We used single nucleotide polymorphism markers to perform a whole-genome scan on 195 pigs experimentally infected with A. suum. A putative quantitative trait locus for worm burden on chromosome 4 covering ∼2.5 Mbp was identified by measured genotype analysis, although none of the SNPs reached genome-wide significance. To validate the putative quantitative trait locus, we genotyped two of the SNPs within the region in unrelated, informative animals exposed to experimental or natural infections and from which we had worm counts and/or faecal egg counts; the validation studies showed that one of the SNPs (TXNIP) was associated with total worm burden (P < 0.001) and adult worm burden (P < 0.0001), whereas the other SNP (ARNT) was associated with adult worm burden (P < 0.025) in these populations. We were thus able to confirm the existence of the quantitative trait locus on chromosome 4. This is to our knowledge the first report of a quantitative trait locus associated with helminth burden in pigs.

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► A whole-genome scan was performed on 195 pigs experimentally infected with Ascaris suum.
► A putative quantitative trait locus (QTL) for worm burden on chromosome 4 covering ∼2.5 Mbp was identified.
► The QTL was validated in unrelated pigs exposed to experimental or natural infections.
► Two single nucleotide polymorphism (SNP) markers were associated with worm burden in experimentally infected pigs.
► Four candidate genes which might be involved in the pig’s response to A. suum infections are presented.