<prompt> Specific test for diagnosis of rickettsial infection -Weil - felix reactionAgglutination of ricketssial suspensionPaul bunnell testRose waaler test  <response>: Ans. is b i.e., Agglutination of ricketssial suspension Both epidemic typhus and endemic typhus are positive for OX-19 antigen - Thus Weil Fleix reaction cannot differentiate between the two.Serological diagnosis of Rickettsial infection Serological diagnosis may be made by :-i Heterophile Weil-Felix reaction.ii Specific tests using rickettsial antigens.A Weil-Felix reaction This reaction is an agglutination test in which sera are tested for agglutinins to O antigens of certain nonmotile proteus strains OX -19, OX - 2 and OX - K. The basis of the test is the sharing of an alkali - stable carbohydrate antigen by some rickettsiae and by certain strains of proteus, P. vulgaris OX - 19 and OX - 2 and P. mirabilis OX - K. The test is usually done as a tube agglutination, though rapid slide agglutination methods have been employed for screening.1 Scrub typhus is positive with OXK.2 Epidemic typhus and endemic typhus are positive for OX-19.3 Rocky mountain spoted fever is positive with OX-19 and OX-2.4 Q fever, trench fever and rickettsial pox do not show positive test with any of the three antigen. Thus Weil Felix test is not useful in these disease.DiseaseOX-19OX-2OX-KRocky Mountain spotted fever-Rickettsial pox---Epidemic typhus--Bril - Zinsser disease---Scrub typhus--Endemic typhus--Trench fever---Q fever---B Specific tests using rickettsial antigens Following antigens are used:-i Group specific soluble antigen - More commonly used.ii Type specific washed rickettsial antigen - Necessary for differentiation between epidemic and endemic typhus. Tests used to detect these antigens are :-i Complement fixation test most commonly used.ii Agglutination of rickettsial suspensions.iii Passive agglutination of red cells sensitized by ESS erythrocyte sensitising substanceiv Toxin neutralisationv Immunofluorescensevi Radioisotope precipitation 