A new rabies test developed at the Centers for Disease Control and Prevention (CDC) could mean that people exposed to animals potentially rabbis could renounce a regime of weeks' strokes to prevent the deadly disease.
The new test, designed for use in animals, can more easily and accurately diagnose infection anger, according to a study published today on PLOS One . The new LN34 test is simpler and easier to use than current tests. During the pilot study, it did not produce false negatives, less false positives and less inconclusive results. It could allow doctors and patients to make more informed decisions about who needs treatment for rabies, which is almost always fatal when the symptoms begin.
The LN34 test can also be performed on test platforms already widely used in the United States and around the world, without any extra training. It also produces results from the decomposition of animal brain tissue. The current gold standard for rabies testing in animals is the direct test of fluorescent antibodies (DFA), which can be interpreted only by laboratory workers 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, testing facilities in many African and Asian countries most affected by rabies are not able to easily rule out the disease in animals that have bitten someone. In these countries, the equipment for testing and supplying of rabies vaccines are often kept in centralized urban areas, several days of travel from where someone is bitten – and the rabies vaccine can cost several months of salary. So knowing if an animal that has bitten someone is rabid is a valuable information.
"Many of the areas most affected by rabies are also the least prepared areas for running current tests to diagnose," said Crystal Gigante, a CDC division microbiologist of pathogens and high-sense succession pathologies and the study's lead author. "The LN34 test has the potential to really change the playing field, to quickly know who needs treatment against rabies and who will not – save lives and livelihoods of families."
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In the recent study, the staff of 14 laboratories around the world evaluated about 3,000 animal brain samples from the Americas, Europe, Africa and Asia, of which more than 1,000 were known to be infected from rabies virus. The samples came from over 60 species of rabies, including dogs, raccoons, skunks, foxes and bats.
LN34 correctly identified all positive samples of DFA as positive. Furthermore, it produced definitive results for 80 samples that were inconclusive or untestable by the DFA test – and 29 of these were rabies positive. Of the 3000 samples tested, LN34 identified a false negative and 11 false positive results for the DFA test. Only one sample was indeterminate using both tests. This study is the largest ever used to validate the use of this type of test (a real-time RT-PCR) to diagnose rabies in animals.
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The LN34 test uses PCR, a testing platform that laboratories around the world already use to test the influence , HIV and tuberculosis. In contrast, DFA tests require a fluorescence microscope, an instrument not always available in environments with fewer public health infrastructures. The LN34 test can be used on fresh animal tissues, frozen, decomposed or fixed in paraffin blocks to inactivate the virus.
The DFA test can only be performed on cold stored fresh brain tissue samples, which can be difficult in areas without reliable electricity. Surprisingly, the researchers found that LN34 was able to detect tiny amounts of rabies virus genetic material, even in such old samples as to be liquefied. Furthermore, the sample condition did not affect the accuracy of the test.
Rabies kills about 60,000 people every year, mainly in Africa and Asia. The disease can take months to develop as a result of a person's contact with a rabid animal. When symptoms appear, anger is almost always fatal, so identifying cases and initiating treatment in advance is critical to a patient's survival. Having a quick, easy to perform and accurate test to tell if an animal that has bitten someone is rabid could help doctors decide if someone needs preventive treatment.
LN34 could also offer benefits for testing in the United States. Currently, if anti-rabies tests are inconclusive, the vise is usually vaccinated against rabies as part of post-exposure prophylaxis, at an individual cost often exceeding $ 3,000. LN34 may reduce the number of inconclusive tests and false positives, eliminating so the unnecessary use of the vaccine. Experts estimate that rabies testing, prevention and control cost $ 245 to $ 510 million annually in the United States. About 40,000 to 50,000 people receive PEP from rabies in the United States each year.
The new rabies test can become part of the international standard
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 the addition of PCR-based tests, such as the LN34 test, for primary diagnosis (in the sense that they could be used as independent tests to confirm rabies, rather than being used with the DFA test).
CDC is working with the Association of Public Health Labs to develop guidelines on anti-rabies testing that will help clinicians and laboratory staff to decide which tests to perform in different scenarios and which tests can be used to confirm the anger, individually or in combination with other tests.