CDC develops easy, accurate rabies test

Published on June 13, 2018

A new assay could improve rabies diagnosis in animals and reduce unnecessary use of postexposure prophylaxis in humans exposed to potentially rabid animals.

The PCR assay, which uses brain tissue from animals submitted for rabies testing, is easier to perform than the standard direct fluorescent antibody test and is accurate even when performed on deteriorated tissue, according to the Centers for Disease Control and Prevention.

A May 16 CDC announcement states that the assay could help doctors and human patients decide who needs postexposure prophylaxis, which can cost more than $3,000. The study results (PLOS One 2018;13:e0197074) indicated the LN34 pan-lyssavirus real-time PCR assay had high sensitivity and produced no false-negative results and fewer false-positive or inconclusive results than the DFA test.

The study involved 3,000 samples of brain tissue collected from 60 mammal species on five continents. About 1,000 tested positive for rabies with the DFA test. The LN34 assay results were used to identify one false-negative and 11 false-positive DFA test results.

DFA testing requires good-quality tissue kept at cold temperatures, a fluorescent microscope, and a technician who can distinguish between rabies antigen and unrelated fluorescence, the article states. In contrast, the LN34 real-time PCR assay requires specific equipment, training, and experience that diagnostic laboratories throughout the world already use for routine infectious disease diagnostic testing. Thus, implementing a rabies assay would be a minimal burden.

Most rabies deaths occur in developing areas, and diagnostic testing could increase in these areas if samples could be stored at room temperature, as is the case for the PCR assay. Storing samples in nucleic acid stabilization buffers could potentially be even better.

The article authors estimate that laboratories using the LN34 assay could detect the presence of as few as eight copies of the rabies virus genome. Three laboratories also tested a panel of 20 samples with the LN34 assay and produced matching results, despite degradation in shipping and differences in laboratories and laboratory personnel.

The CDC announcement also states that the World Health Organization and World Organisation for Animal Health (OIE) are considering whether the PCR assay should be used for primary rabies diagnosis.

In the announcement, Crystal Gigante, a microbiologist in the CDC Division of High-Consequence Pathogens and Pathology and the article's first author, said, "Quickly knowing who needs to receive rabies treatment—and who does not—will save lives and families' livelihoods."