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Rabies: CDC develops new rapid test, could lead to fewer shots



A new rabies test developed at the Centers for Disease Control and Prevention (CDC) could mean that people who are potentially exposed to rabies can forego weeks of vaccination to prevent the deadly disease ,

  Rabies virus Image / CDC
Rabies virus
Image / CDC

The new test, developed for use in animals, can now be found in PLOS One according to a study to diagnose a rabies infection easier and more accurate. The new LN34 test is easier and easier to use than current tests. During the pilot study, no false-negative, less false-positive and less-than-inconclusive results were achieved. It could enable physicians and patients to make better-informed decisions about who has to treat rabies, which is almost always fatal when the symptoms begin.

The LN34 test can also be performed on test platforms that are already widely used in the US and worldwide for any additional training. And it provides results even of decomposing animal brain tissue. The current gold standard for animal rabies testing is the Direct Fluorescence Antibody (DFA) test, which can only be interpreted by laboratories with special abilities, extensive training and a specific type of microscope.

The new test could help improve rabies testing in the United States and in resource-poor countries. Currently, in many countries in Africa and Asia most affected by rabies, testing facilities can not easily exclude the disease in animals that have bitten someone. In these countries, kits for testing and rabies vaccines are often kept in centralized urban areas, away from where someone is bitten for several days – and the rabies vaccine can cost several months' salaries. Knowing whether an animal that bites someone is rabid is valuable information.

"Many of the areas most affected by rabies are also the least eager to perform current tests to diagnose them," said Crystal Gigante, a microbiologist in the CDC department of high-consequence pathogens Pathology and the first author of the study. "The LN34 test has the potential to really change the playing field, knowing quickly who has to receive rabies treatments – and who will not – saving lives and livelihoods for families."

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In the current study, staff from 14 labs worldwide evaluated nearly 3,000 animal brain samples from America, Europe, Africa, and Asia, of which more than 1,000 were known to be infected with rabies virus. The samples came from more than 60 species of mammals that received rabies, including dogs, raccoons, skunks, foxes and bats.

LN34 correctly identified all DFA-positive samples as positive. In addition, final results were obtained for 80 samples that were not clear or provable with the DFA test – and 29 were positive for rabies. Of the 3,000 samples tested, the LN34 identified one false negative and 11 false positive DFA test results. With both tests, only one sample was indefinite. This study is the largest so far to validate the use of this type of test (a real-time RT-PCR) for the diagnosis of rabies in animals.

New rabies test … Greater flexibility

LN34 tests with PCR, a test platform that is already being used worldwide for testing for influenza, HIV and tuberculosis. In contrast, DFA testing requires a fluorescence microscope, an instrument that is not always available in environments with less public health infrastructure. The LN34 test can be used on animal tissue that is fresh, frozen, degraded or fixed in blocks of paraffin to inactivate the virus.

The DFA test can only be performed on fresh brain tissue samples that have been stored cold, which can be difficult in areas without reliable electricity. Surprisingly, the researchers found that LN34 was able to detect minute amounts of rabies virus genetic material, even in samples that were so old that they had liquefied. In addition, the condition of the sample did not affect the accuracy of the test.

Rabies kills around 60,000 people annually, mainly in Africa and Asia. It can take months for a person to develop contact with a rabid animal. Once the symptoms appear, rabies is almost always fatal. Therefore, it is crucial for the survival of a patient to identify cases and to begin treatment early. With a quick, easy-to-use and accurate test, you can see if an animal biting someone is rabid and can help doctors decide if someone needs preventive treatment.

LN34 could also provide benefits for testing in the United States. Currently, when rabies tests are ambiguous, the bitten person is usually given as part of the post-exposure prophylactic rabies vaccine, at a cost often over $ 3,000. LN34 could reduce the number of inconclusive and false positives, avoiding unnecessary vaccinations. Experts estimate that rabies testing, prevention and control costs between $ 245 and $ 510 million annually in the United States. About 40,000-50,000 people receive rabies PEP annually in the US.

New rabies test can become part of international standard

Currently, the DFA test is the only internationally recognized test for confirming rabies in animals. However, the World Health Organization and the World Organization for Animal Health are considering adding PCR-based tests such as the primary diagnosis LN34 test (which means they could be used as stand-alone tests to confirm rabies)

CDC works with the Association of Public Health Laboratories to develop rabies test guidelines that will help clinicians and laboratory staff decide which tests to run in different scenarios and which rabies confirmation tests can be used, or in combination with other tests.


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