An amino acid motif present in 5 BoLA-DRB3 alleles is a highly significant genetic marker of susceptibility to bovine dermatophilosis

In Martinique Island (F.W.I.), zebu Brahman cattle suffer from severe dermatophilosis infections, inducing a loss in productivity and a 15% mortality. Currently, no vaccine is expected and chemoresistance phenomena decrease the means of control. Considering a 6-year long ecopathological survey on 568 animals from several herds, we classified 118 unrelated animals of both sexes, reared in the same environmental conditions, in two extreme groups. The most resistant individuals (n=45) were never infected whereas the susceptible individuals (n=73) showed severe clinical signs and died. The polymorphism in exon 2 of the BoLA-DRB3 gene was analysed using the PCR-RFLP technique. Comparing the allele frequencies within both extreme groups, we identified 2 PCR-RFLP patterns (FDA and GEA) corresponding to the five official alleles DRB3.2*0301, DRB3.2*0302, DRB3.2*0901, DRB3.2*0902 and DRB3.2*1202, which are the only ones, amongst the 75 official DRB3.2 alleles, having a particular amino acid motif ES (glutamic acid-serine) in positions 20 and 22 of exon 2 of this gene. The difference of frequences of this ES motif (S.fq.=0,589 vs R.fq.=0,004) is highly significant (x square = 32,7; P value<0.0001) indicating that it is a strong marker of susceptibility to this disease. However, amongst the 568 typed animals, 45 of them had this ES marker of which 43 (95,6%) were classified as susceptible. A eugenic selection based on the elimination of animals having this prediction marker of susceptibility has been giving excellent results for 2 years in several herds with a very significant decrease of the disease prevalence from 0.768 to 0.198. Family studies are in progress to study the transmission of this marker. (Résumé d'auteur