Nadia, the Bronx Zoo tiger recently diagnosed with coronavirus, did NOT deprive a potentially infected person from getting a COVID-19 test
There’s been some public blowback against officials for giving Nadia, an ailing Malayan tiger who lives at the Bronx Zoo, a test for coronavirus. Considering that tests for COVID-19 are so severely limited for humans, why should a sick tiger get a test before a sick person does?
Although councilman Ritchie Torres voiced a common frustration, this sentiment reflects the confusion surrounding COVID-19 testing because there are two main differences between COVID-19 tests for humans and those used for animals. The first difference lies in the test itself, and second difference is the labs that administer these tests.
Nadia the tiger was not diagnosed with a human COVID-19 test
“Testing performed on animals is based on the published tests used in people, however the National Veterinary Services Laboratories uses reagents not required when testing people”, said Lyndsay Cole, Assistant Director of Public Affairs with the USDA Animal and Plant Health Inspection Service (USDA-APHIS), which is the facility that confirmed Nadia the tiger’s initial positive COVID-19 test.
The conditions under which a sample is collected can make all the difference in its usefulness.
“PCR can be amazingly sensitive but false positives are a problem in uncontrolled environments like hospitals with sick employees”, said Edward Dubovi, Professor of veterinary medicine at Cornell University, which initially discovered that Nadia was infected with SARS-CoV-2. Professor Dubovi is expert in several areas, including viral diseases of domestic animals that impact endangered wildlife.
Although the USDA is not recommending routine coronavirus testing of animals, a small number of animals in the United States have been tested by the USDA’s National Veterinary Services Laboratories, and all those tests came back negative — except Nadia’s.
But a positive PCR test does not mean the virus is actually present.
“PCR positive does not mean infectious virus was found, which muddies the water as to the period of time when infectious virus is shed. RNA signals exist in some situations long after the infectious virus is gone”, Professor Dubovi explained in email.
An active — or very recent — infection with coronavirus can be detected using a highly sensitive PCR-based test that detects the RNA of the SARS-CoV-2 virus.