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What is Specific test for diagnosis of rickettsial infection - and explain in detail?
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 substance)iv) Toxin neutralisationv) Immunofluorescensevi) Radioisotope precipitation