Rabies diagnosis in animals - Pasterov zavod

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Rabies diagnosis in animals


The direct fluorescent antibody test (DFA) is most frequently used to routine diagnose of rabies. This test can be performed on brain tissue of animals suspected of being rabid. The rapid and accurate laboratory diagnosis of rabies infections in animals is essential for timely administration of postexposure prophylaxis. Within a few hours, a diagnostic laboratory can determine whether or not an animal is rabid and inform the responsible medical personnel. The laboratory results may save a patient from unnecessary physical and psychological trauma, if the animal is not rabid. All rabies laboratories in the Yugoslavia (3) perform this test on animals suspected of having rabies.

The DFA test is based on the principle that an animal infected by rabies virus will have rabies virus antigen present in its tissue. Because rabies is present in nervous tissue (and not blood like many other viruses) the ideal tissue to test for the presence of rabies antigen is brain. The most important part of a DFA test is flouresecently-labelled anti-rabies antibody. Pasteur Institute in Novi Sad produced fluorescent-labelled anti-rabies antibody on hamsters and goat. When labeled antibody is added to rabies-suspect brain tissue, it will bind to rabies antigen if it is present. Unbound antibody can be washed away and the areas where the antigen has bound antibody will appear as a bright fluorescent apple green color when viewed with a fluorescence microscope. If rabies virus is absent there will be no staining. The rabies antibody in the DFA test is primarily directed against the nucleoprotein (antigen) of the virus. Rabies virus replicates in the cytoplasm of cells, and infected cells may contain large round or oval inclusions containing collections of nucleoprotein (N) or smaller collections of antigen that appear as dust-like fluorescent particles if stained by the DFA procedure.

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