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