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Armed with new diagnostic tools, scientists found
the infection to be in many countries and many animal species.
Experimental infection studies discovered the surprising age-dependent
susceptibility to M. paratuberculosis infection.
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Paratuberculosis was described
in South America and on the Indian continent during the 1930s,thereby completing
evidence of the worldwide distribution of the disease. That decade brought about
a broader realization that paratuberculosis jeopardized the cattle industry. A
major achievement of the 1930s was the observation of age-dependent resistance
of animals to infection by M. paratuberculosis.
In the 1940s, paratuberculosis was recognized to be a problem not only in
domesticated livestock, but in wildlife as well. Paratuberculosis was observed
to have many similarities with human leprosy. Continued evaluation of diagnostic
tests led to the discovery of cross-reactivity, resulting in false-positive
tests, with bacteria in the genus Corynebacterium and other antigenically-related
bacteria.
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