FEBRILE ANTIGENS

Febrile Antigen  tests are used in the detection of antibodies produced in certain febrile  diseases such as salmonellosis, brucellosis and rickettsial diseases. Febrile  antigen tests are serological applications of the classical Widal reaction for  the diagnosis of typhoid fever and the Weil-Felix test reactions where antigens  prepared from Proteus organisms are used to detect related rickettsial  antibodies.

Serological  diagnosis of patients suspected of having infectious diseases characterized by  persistent fever is dependent upon demonstration of an agglutination reaction  between the appropriate antigen and antibody.

The natural  response to the invasion of pathogenic organisms is the production of  antibodies. This immune response is highly individualized and in addition to  the host’s physiological status and genetic capabilities, a number of other  factors are involved in the production of antibodies to the particular  stimulus. These include the antigenicity of the organism, the total amount  introduced to the host and the route of introduction, and whether the host has  had previous exposure to the organism. These factors will determine the rate of  antibody formation, the amount of antibodies produced and their persistence in  the circulatory system.

The patient’s  serum is tested directly for specific antibodies by either slide or tube  agglutination test. These tests are qualitative and semi-quantitative. The  rapid slide test is used primarily as a screening procedure especially useful  when large numbers of sera must be examined. The tube test should be used to  confirm positive results obtained by the slide test.