Effect of Ovar‐DRA and Ovar‐DRB1 genotype in small ruminants with haemonchosis

Abstract

The effect of Ovar-DRA and Ovar-DRB1 genotypes on faecal egg count (FEC) was determined in sheep and goats infected with Haemonchus contortus. One hundred and forty-three sheep from 3 different breeds (St. Croix, Katahdin and Dorper) and 150 goats from three different breeds (Spanish, Boer and Kiko) were used. Parasitological (FEC), haematological (packed cell volume) and immunological (IgA, IgG and IgM) parameters were measured. Sheep populations showed a higher FEC and humoural response than goat breeds. Genotypes were determined by high-resolution melting assays and by conventional PCR. For Ovar-DRA, sheep and goats carrying the AA genotype showed significant lower FEC than AG and GG genotypes. The additive effect was found to be 115.35 less eggs per gram of faeces for the A allele for goats. For Ovar-DRB1, only in sheep, the GC genotype was associated with low FEC. The additive effect was 316.48 less eggs per gram of faeces for the G allele, and the dominance effect was 538.70 less eggs per gram of faeces. The results indicate that single nucleotide polymorphisms within Ovar-DRA and Ovar-DRB1 could be potential markers to be used in selection programmes for improving resistance to Haemonchus contortus infection.

Association of MHC class II haplotypes with reduced faecal nematode egg count and IgA activity in British Texel sheep

“…12,13 Several groups have shown associations between genetic variants in the MHC and faecal egg counts. 5,[14][15][16][17] In particular, the DRB1*11:01 allele has been associated with lower faecal egg counts in Scottish Blackface 5 and Suffolk sheep. 15 However, this association was not confirmed in a population of Texel sheep.…”

“…The association between the MHC and nematode infection of sheep is one of the most convincing examples of an association with a major disease of livestock . Several groups have shown associations between genetic variants in the MHC and faecal egg counts . In particular, the DRB1*11:01 allele has been associated with lower faecal egg counts in Scottish Blackface and Suffolk sheep .…”

A novel technique for retrospective genetic analysis of the response to vaccination or infection using cell-free DNA from archived sheep serum and plasma

“…MHC genotype can impact on host responses to parasitic disease by influencing the range of antigenic peptides presented for recognition by the adaptive immune system. Numerous studies have shown the relevance of MHC diversity on resistance or susceptibility to infection with nematode parasites in many species including mice [25,26], sheep [8][9][10][11][12] and cattle [27]. However, MHC genotyping has relied on the availability of cell or tissue samples for DNA extraction.…”

“…No specific DRB1 alleles have previously been associated with resistance to H. contortus infection although microsatellite [10] and single nucleotide polymorphisms within Ovar-DRB1 have been identified in resistant and susceptible sheep from St. Croix, Katahdin and Dorper breeds [12]. One DRB1 allele (11:01) has been associated in Suffolk sheep with lower worm burdens and higher mast cell and plasma platelet counts following infection with the GIN Teladorsagia circumcincta [36] and with reduced faecal egg count in Texel breed sheep [41].…”

“…Previous studies have identified associations between MHC diversity and resistance or susceptibility to gastrointestinal nematodes (GIN) infection in different sheep breeds [8][9][10][11][12]. MHC influence on the response to GIN vaccination has not been examined.…”