More warnings in the U.S. were issued about this spreading infectious disease. Immunology was a new scientific discipline and immunologists focused on the biology of the infection and developed more tools for diagnosis.

"Johne's disease may become very prevalent and troublesome in the United States unless more attention is given to its diagnosis and control."

Warnings from the U.S. Department of
Agriculture (circularmo. 873, page 3, 1951)

Also in 1951 an astute Dutch scientist, Jacob Jansen, observed an association between soil pH and the incidence of Johne's disease (J.Am.Vet.Med.Assoc. 112:52-54,1951). This is the first reported observation that environmental factors may influence occurrence of the disease.

Vaccination as a means to control paratuberculosis was the subject of many studies in the1950s. In addition, various strains of M.paratuberculosis were recognized during that decade including pigmented variants and strains that failed to grow on artificial culture media.

The young scientific discipline of immunology brought its techniques to bear on the study of paratuberculosis in the 1960s. More diagnostic tests, such as the leukocyte migration and fluorescent antibody tests, were devised and evaluated. The 1960s saw renewed efforts to find an acceptable laboratory animal model of Johne's disease. Important epidemiological observations were made in this era: 1) clinically normal but infected animals (carriers) actively excreted M. paratuberculosis in their feces, and 2) M. paratuberculosis could be found in the semen of infected bulls and the uterus of infected cows indicating the possibility of intra- or trans-uterine infection of fetuses.