Weil Felix Reaction
It is a heterophile agglutination test used for the serodiagnosis of typhus fever. It is based on the principle that the agglutinins present in the serum of patients suffering from typhus fever agglutinate agglutinogens (O antigens) of certain non motile strains of proteus. (OX 19, OX 2 OX K). It is commonly done as a tube agglutination test, but can also be done as rapid slide agglutination test in screening.
The basis of this test is the sharing of an alkali stable carbohydrate antigen between certain non motile proteus strains and some rickettsiae .
The test becomes rapidly positive during infection and reaches titres of upto 1:1000 to 1:5000 in second week. The titres fall rapidly during convalescence. False positive reaction can occur in infections by proteus, typhoid fever and liver disease. Hence demonstrating a rise in titre is more reliable method for diagnosis of rickettsial disease.
The test is negative or weakly positive in Brill Zinsser disease. It is negative in rickettsial pox, trench fever, Q fever.