Ricketsial disease with positive Weil-Felix reaction by only OX-19 ?

Ans. is 'a' i.e., Epidemic typhus Weil felix reaction This reaction is an agglutination test in which sera are tested for agglutinins to 0 antigens of ceain 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 ceain 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.