G'day Bella.The link suggested by Lanasvet is excellent & well worth the read.This is my" feeling" on ovine johne's disease ,OJD as we call it in OZ."Ovine" means sheep (maggot taxies),the best way to manage" most" deer herd health issues is keep them as far from sheep as possible.I have only heard of one group of deer (fallow) going clinical in this country.They were kept under high density,under nutritional stress & surprise, surprise,shared pasture with sheep.This is only my opinion,I feel that animals may carry OJD,however it only goes clinical when an animal is under stress(nutritional,environmental,capture,transport,etc).I would like to know, if it gets passed on when it doesn't go clinical? Down here OJD is reportable so we can try to manage it, and regions are rated as to their potential risk so potential purchasers can weigh the pros & cons & manage their own risk.I have had my animals tested & its a few anxious weeks waiting for a negative.I would strongly suggest if you suspect OJD test for it & then make some thoughtful decisions.Once it is on your pasture I think it may just be a matter of management.This was a red hot topic in 2005 when the drought was really biting (nutritional stress),in the last 12 months, silence.This is just my opinion so if you have issues consult your vet. Sharkey