Presence of Cross-Reactions with Other Viral Encephalitides in the Indirect Fluorescent-Antibody Test for Diagnosis of Rabies

Abstract

The antemortem diagnosis of rabies in humans employs techniques that require accuracy, speed, and sensitivity. A combination of histochemical analysis, in vitro virus isolation, immunological methods, and molecular amplification procedures are utilized in efforts to diagnose the disease. Modern medicine now offers potentially life-saving treatment for a disease that was considered invariably fatal once clinical signs develop. However, medical intervention efforts require a rapid and accurate diagnosis as early in the course of clinical disease as possible. Indirect fluorescent-antibody (IFA) testing on cerebrospinal fluid and serum specimens provides rapid results, but the specificity of the assay has not been well studied. Because false-positive IFA results could significantly affect patient treatment and outcomes, it is critical to understand the specificity of this assay. In this study, IFA testing was performed on 135 cerebrospinal fluid and serum specimens taken from patients with viral encephalitis or a presumed viral infection involving an agent other than rabies virus. Results indicate that false-positive results can occur in interpreting the rabies IFA test. Staining patterns morphologically similar to antirabies staining were observed in 7 of the 135 cerebrospinal fluid specimens examined. In addition, a majority of the cerebrospinal fluid specimens tested from patients with encephalitis presented immunoglobulin that bound to antigens present in the cell culture substrate. Of marked concern was the frequent presence of cross-reactive antibodies in encephalitis cases associated with West Nile and Powassan flaviviruses. Because IFA testing for rabies on human specimens may result in false-positive results, it should not be used as the sole basis for initiating antirabies treatment. Rapid accurate antemortem rabies diagnosis in humans has been imperative for palliative patient care and for treatment of individuals potentially exposed to the patient. The Milwaukee protocol (1) was introduced as a potentially life-saving treatment for human rabies, and the sooner the protocol is initiated the greater the chances of success. This paradigm demands speed and accuracy from the rabies diagnostician. The test most likely to provide a quick rabies diagnosis is the direct fluorescent-antibody (DFA) test (see Protocol for Postmortem Diagnosis of Rabies in Animals by Direct Fluorescent Antibody Testing [www.cdc.gov /rabies/pdf/RabiesDFASPv2.pdf]) performed on a nuchal skin biopsy specimen from the patient. However, since the results of this test may be negative in earlier stages of the disease, other procedures are relied upon and are carried out concurrently with the DFA test. The indirect fluorescent-antibody (IFA) test performed with cerebrospinal fluid (CSF) and serum specimens from rabiessuspect patients can yield results within a few hours. To perform an IFA test, serial dilutions of serum or CSF samples are placed on fixed, rabies virus-infected, cultured cells. If the serum or CSF contains antibodies to rabie...

Duration of serum antibody response to rabies vaccination in horses

“…Use of prevaccination RVNA values and serologic responses 3 to 7 weeks after vaccination to infer the prior vaccine history was potentially misleading because vaccinated horses may have had RVNA values that were lower than the LOD of the assay used, and unvaccinated horses may have had cross-reactive antibodies or other nonspecific inhibitors of virus that can mimic specific antibody in laboratory testing. [37][38][39][40] In addition, interpretation of serologic data to determine grouping may have introduced some degree of bias.…”

Virology, Immunology and Pathology of Human Rabies During Treatment

“…2,26,27 Confirmation of the diagnosis of the 2011 India survivor is uncertain while the diagnosis of the California and Texas survivors relied on immunofluorescence assays that have been challenged. 28 The 2011 California survivor did not mount a RABV-neutralizing antibody response. 26 The putative rabies survivor in Texas showed mild symptoms, like the India survivor, and did not show consistent RABV-neutralizing antibody in serum or CSF, like the California survivor.…”

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“…The activity and specificity of the antigenic fractions most satisfying the requirements were evaluated in ELISA [10] and IFA [11] using certified diagnostic kits.…”