[Immunohistochemical diagnosis of Mediterranean spotted fever: detection of rickettsial antigens in the initial skin lesions].

In eight patients with Mediterranean spotted fever we evaluated the yield of the direct immunofluorescence technique against rickettsial antigens for the early laboratory diagnosis of the disease. Frozen sections of biopsy specimens of the initial lesion (tache noire) taken on the admission day were processed by a fluorescent conjugate reactive against Rickettsia conorii. In seven cases, coccobacillary formations consistent with rickettsiae were observed in the studied specimens. The results were negative in the controls and in three of six samples of exanthema elements obtained from six simultaneously studied patients with Mediterranean spotted fever. Our data demonstrate the diagnostic value of direct immunofluorescence applied on the tache noire. This technique is particularly useful in the initial stages of the disease, before the clinical and serological features have completely developed.