However, to date this research has not been confirmed and the organism has not been cultured from human cases. The jury is still out on this one. There is a cattle strain, a sheep strain and an intermediate strain. While cattle are susceptible to all three strains, they are usually not infected with the sheep strain. Sheep usually get only the sheep strain but can also succumb to the intermediate strain.
Goats usually have the cattle strain.
The Clinical Disease Johne's disease in a flock or herd behaves very much like an iceberg. The disease that a shepherd may see in the flock represents only a small proportion of sheep that are actually infected. Sheep can become infected at any age, but if infected while a lamb or fetus, then the disease manifests itself as young as 18 months. An astute shepherd may notice nothing more than a ewe that seems to be a little thinner than the rest of the flock. Sometimes another stress such as lambing or mastitis will hasten the onset of more severe clinical disease.