May 16th 2018

A new rabies test developed at the CDC could mean people exposed to potentially rabid animals would forego the weeks-long regimen of shots to prevent the deadly disease.

A new rabies test developed at the CDC could mean people exposed to potentially rabid animals would forego the weeks-long regimen of shots to prevent the deadly disease. The test, designed for use in animals, can more precisely diagnose rabies infection, according to a study published today inPLOS One.

The current gold-standard for rabies testing in animals is the direct fluorescent antibody (DFA) test, which can only be interpreted by laboratory workers with special skills, extensive training, and a specific type of microscope. The new LN34 test is simpler, and easier to use than current tests.

During the pilot study, the LN34 test produced no false negatives, fewer false positive results, and fewer inconclusive results, than the DFA. The new test could allow doctors, and patients to make better informed decisions about who needs treatment for rabies, which is nearly always fatal once symptoms start.

LN34 testing uses PCR, a testing platform that labs worldwide already use to identify flu, HIV, and tuberculosis. In contrast, DFA testing requires a fluorescent microscope, an instrument not always available in settings with less public health infrastructure. The LN34 test can be used on animal tissue that is fresh, frozen, decomposed, or that has been fixed in blocks of paraffin to inactivate the virus.The DFA test can be run only on fresh brain tissue samples that have been kept cold, which can be difficult in areas without reliable electricity.

Currently, testing facilities in many countries in Africa and Asia most affected by rabies are not able to easily rule out the disease in animals that have bitten someone. In these countries, equipment for testing and rabies vaccine supplies are often held in centralized urban areas, several days’ travel from where someone is bitten—and rabies vaccine can cost several months’ salary. The new test could help improve rabies testing in resource-poor countries, as well as the United States.

“Many of the areas hardest hit by rabies are also the areas least prepared to run current tests to diagnose it,” said Crystal Gigante, a microbiologist in CDC’s Division of High-Consequence Pathogens and Pathology and a study author, in a statement. “The LN34 test has the potential to really change the playing field. Quickly knowing who needs to receive rabies treatment—and who does not—will save lives and families’ livelihoods.”

In the recent study, staff at 14 labs worldwide assessed nearly 3,000 animal brain samples, of which more than 1,000 were known to be infected with rabies virus. The samples came from more than 60 mammal species that get rabies, including dogs, raccoons, skunks, foxes, and bats.

LN34 correctly identified all DFA-positive samples as positive. In addition, it produced definitive findings for 80 samples that had been inconclusive, or untestable by the DFA test—and 29 of those were positive for rabies. Of the 3,000 samples tested, the LN34 identified one false negative, and there were 11 false positive DFA test results. Only one sample was indeterminate using both tests.

Currently, the DFA test is the only internationally approved test to confirm rabies in animals. However, the World Health Organization and the World Organization for Animal Health are considering adding PCR-based tests, such as the LN34 test, as a primary resource. The CDC is working with the Association of Public Health Laboratories to develop rabies testing guidance that will help clinicians, and laboratory staff decide which tests to run in different scenarios and which tests can be used to confirm rabies, either singly or in combination with other tests.

Reference

New rapid rabies test could revolutionize testing and treatment [news release]: Atlanta, GA; May 16, 2018. CDC website. https://www.cdc.gov/media/releases/2018/p0516-rapid-rabies-test.html. Accessed May 16, 2018.

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