Report on the Agricultural Experiment Stations, 1953 Page: 25
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LIVESTOCK PRODUCTION AFFECTED BY ANIMAL DISEASES 25
The natural reservoir of Listeria mzonocytogenes has never been
determined. This has retarded the study of the disease in both animals
and man. There is increasing evidence that the micro-organism is
widely distributed in nature, perhaps in the form of a soil bacterium
or as a saprophyte, and that only under specific conditions does it
occur as a pathogen. It was felt at the Michigan station that failure
to isolate this organism from sources other than the animal body,
reflected a failure to recognize it in its nonpathogenic form. A study
of the dissociation pattern of L. mfonocytogenes is in progress in an
effort to identify the various colonial forms in which this bacterium
might occur. So far nine colonial forms have been identified, some
rough and others smooth. Only the smooth form is highly pathogenic
for laboratory rabbits when inoculated intravenously.
Biochemically, the rough forms are very similar to the smooth, and
several of those tested produced high-agglutinating antibody titers
against the smooth form when inoculated intravenously into rabbits;
however, on subsequent challenge they afforded no protection. Additional
investigations are in progress at this and other stations to
provide needed information on effective methods of diagnosis, mode
of transmission, methods of treatment, and a system of control for
Bluetongue in California sheep
In September 1952 a disease of sheep which causes severe mouth
lesions, weight loss, and costly decline in wool quality made its appearance
in California flocks. Affected sheep exhibited symptoms
almost identical to those observed in flocks of Texas and Utah where
it is known as sore-muzzle. As a result of studies of this disease, a
virus has been isolated and identified as that causing bluetongue, a
disease known in South Africa since the turn of the century, where
it has been a cause of serious economic loss. California station veterinarians
are now attempting to reduce the virulence of the virus by
passing it through eggs and thus making it possible to produce a
modified live virus vaccine similar to the one being used with great
success in South Africa. In the continuing experiment, virus will be
imported from sore-muzzle sheep of Texas and Utah to determine
whether all the disease strains in the United States are the same. . If
the strains differ, all will be incorporated in the vaccine. Entomologists
of this station are searching for the vector, or vectors, of the
bluetongue virus, which in South Africa has been shown to be a gnat.
External parasites of domestic animals exact a continuing toll from
livestock. Flies have been accepted in the past as a natural nuisance
on and around livestock and a few lice or ticks often go unnoticed,
but the annual loss from total tick, mite, or insect depredations is
heavy. When external parasites carry disease or occur in such numbers
as to cause epidemics, known controls are applied if they are
practical under local conditions. Such measures are based on research
aimed to protect farmers from reduced production through the lowered
efficiency of their animals. The following are examples of successful
external parasite control measures growing out of station research.
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United States. Office of Experiment Stations. Report on the Agricultural Experiment Stations, 1953, book, 1953; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc5989/m1/27/: accessed April 30, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.