Genetic epidemiology and familial risk factors for paratuberculosis seropositivity in beef cattle

摘要

Paratuberculosis is an intestinal infection of ruminants caused by Mycobacteriumavium subsp. paratuberculosis (MAP). Genetic associations with paratuberculosis havebeen described in Holstein cattle. The objectives were to describe the associationbetween paratuberculosis status of the dam and her offspring in beef cattle, developmethods to assess familial aggregation of paratuberculosis in cattle of unknownpedigree, and model the paratuberculosis status of beef cattle given familial and herdlevelcovariates. Texas beef cattle were tested for paratuberculosis using serum antibodyand microbiologic culture of feces. Available pedigree data were used to confirmfamilial relationships.The association between the paratuberculosis ELISA status of the dam and heroffspring was assessed using mixed-effects models. Increased odds of being classified asa ?suspect? or greater based on ELISA results were observed if the dam was classified asa ?suspect? or greater. A positive linear association was observed between the ELISAvalue of the dam and her offspring. Analysis of pedigree data using conditional logistic regression identified ancestors associated with significantly increased odds of beingclassified as ?low positive? or greater.Microsatellite markers were used to classify cattle into genetically similar groupsusing allele frequency data. Nine clusters of genetically similar cattle were identifiedamong paratuberculosis test positive cattle, herd matched controls, and pedigreed cattle.Clusters were validated using animals of known pedigree. Increased odds ofparatuberculosis seropositivity were observed for some clusters compared to the clusterwith the lowest seroprevalence.A predictive model was developed using a Bayesian framework to assess theassociation between antibody status of the dam and her offspring adjusted for herd-levelrisk factors. Predictors associated with highly probable increased odds of seropositivityincluded herd seroprevalence and herd fecal prevalence of MAP. The associationbetween dam and offspring ELISA status was small (OR 1.35) and not highly probable.The results of this work support familial aggregation of paratuberculosis ELISAstatus, but herd-level risk factors appear to be more important in predicting ELISAstatus. A large proportion of observed serological reactions were not supported by fecalculture results; therefore, observed associations might be limited to humoral responses toMycobacterium spp.