Answer 87 - Rickettsiae
Rickettsiae:
True a. cannot be cultured on artificial media
True b. may cause an eschar
True c. are spread by arthropods
True d. are usually sensitive to tetracyclines
False e. cause melioidosis
They grow in chick eggs and in tissue culture. Laboratory diagnosis relies on paired serological tests (IFAT or ELIZA). The Weil-Felix test is a non-specific, non-sensitive serological test that is sometimes used in the diagnosis of rickettsial disease. Treatment should be started when a clinical diagnosis is made.
Escars occur in tick typhus, scrub typhus and rickettsial pox but not in epidemic typhus. Similar skin lesions may be seen in anthrax, plague and trypanosomiasis (trypanosomal chancre).
Riskettsiae are sensitive to tetracyclines, chloramphenicol and quinolones. As treatment is usually empirical it is often necessary to also cover typhoid.
Tetracycline does not cover typhoid.
Melioidosis is caused by Pseudomonas pseudomallei.
