Diagnosis of rickettsial diseases: A perspective

Abstract

Rickettsioses have nonspecific clinical manifestations, making them difficult to diagnose in a clinical setting. Laboratory testing is usually needed to confirm the diagnosis. Rickettsial isolation is a sensitive and specific diagnostic technique, but the hazards associated with handling pathogenic rickettsiae usually preclude isolation attempts in most laboratories. Rickettsiae can also be detected in infected tissues by fluorescein-labeled antisera or by immunoperoxidase staining, but these techniques lack sensitivity, except when applied to postmortem tissue specimens. However, rickettsial DNA can be detected in acute phase blood specimens by polymerase chain reaction (PCR) technology, and this technique offers the prospect of prompt diagnosis and treatment. Serologic testing remains the most frequently used approach to diagnosis, although antibody tests usually fail to identify rickettsioses early enough to affect the management of individual patients. Available serologic techniques vary considerably in their sensitivity and specificity. Enzyme-linked immunosorbent assays (ELISA) are extremely sensitive, but the general unavailability of specific diagnostic antigens reduces the specificity of this and other serologic techniques. Molecular characterization of rickettsial antigens may soon allow the production of peptide antigens that are specific for each species and could maximize the specificity of test results. No diagnostic technique has any value unless it is applied successfully to the appropriate patient population. Improved surveillance of rickettsial diseases is urgently needed to identify specific areas in which rickettsioses are endemic. Such surveillance data would promote awareness of rickettsioses among local physicians and increase the probability that individual patients with rickettsioses would be identified promptly and receive appropriate therapy early in the course of their illness.

Diagnosis of Q Fever

“…Interpretation of results of serological testing. The predictive value of positive and negative results is affected by the prevalence of the disease, creating a certain degree of background antigen stimulation in the studied population (115). Therefore, the determination of cutoff values is very important for the interpretation of the serological results (Table 3).…”

Epitope mapping of the Sta58 major outer membrane protein of Rickettsia tsutsugamushi

“…Of interest also is the finding that the reactive peptides bind primarily to IgM in the sera, perhaps reflecting recent infection with R tsutsugamushi. Should some of these epitopes indeed prove to be scrub typhus specific, they may be valuable as pure diagnostic antigens in order to improve the sensitivity and specificity of serologic diagnosis (8). It should also be pointed out that the present study has not directly addressed the question of the absolute specificity of the peptides through absorption studies with native antigen or free peptides and that specificity is inferred from nonreactivity of normal sera and sera from patients with other illnesses common to the region.…”

Optic Neuropathy From Bacteria

“…66 Serology, the usual method for confirmation of the clinical diagnosis, is retrospective regardless of the method used, because serum antibodies to Rickettsia rickettsii only become detectable during convalescence. [67][68][69][70][71] Although new immunologic tests, including restriction-endonuclease length polymorphism analysis using the PCR, are constantly being developed to both rapidly and accurately diagnose Rocky Mountain spotted fever [72][73][74][75][76][77] early clinical diagnosis remains essential if one is to treat the condition effectively.…”