Can we get rapid tests for avian influenza?

During the coronavirus pandemic, humans weren’t the only ones who suffered massive amounts of infections. Birds were also struck heavily: avian influenza spread like wildfire, both among poultry and wild birds. Inspired by the rapid tests developed for humans, the North Holland veterinarian Miriam Bosman wondered whether it was possible to rapidly track down avian influenza in a similar manner. She had the idea of trying an antigen test for humans on birds – and this appeared to work. The test, which is normally used to detect Influenza A, was promising enough to draw the attention of the national avian influenza platform of Rijksoverheid.

Denise Smit, policy officer of Animal Health & Antibiotics Policy at the Ministry of Agriculture, Fisheries, Food Security and Nature (LVVN) and veterinarian, explains that the ministry opted for a consciously curious approach to this development. ‘You could ignore these kinds of developments. However, in light of our duty to inform and protect, we thought it was important to ascertain how well a human test like this could work. And who knew? Maybe these animal ambulance employees were onto something.’

User-friendly and sensitive

Fimme van der Wal, researcher at WBVR, headed the study. ‘It is not too surprising that a human rapid test works for avian influenza. After all, they are both Influenza A viruses.’ The first stage of the study was aimed at finding a readily available, user-friendly and, of course, reliable rapid test. ‘The rapid test will never fully replace the PCR-test in our reference laboratory. The consequences of a positive test are simply too significant. However, if a human rapid test were sensitive enough, it could supplement the current protocol.’

Van der Wal and his colleagues started by gathering information about available rapid tests for Influenza A. ‘There are tests for people, and then there are specialised tests for avian influenza. We proceeded by making a selection. Since the test might be performed at farms, as a sort of pre-screening process, we were looking for a straightforward, convenient test.’ A test that required pouring half a vial into another, after which a loose strip had to be placed in the latter vial and consulted for the result was immediately scratched off the list. ‘It had to be as easy as the well-known self-tests for the coronavirus’

In their selection, the researchers had a preference for European or North American tests. Products from Asia were subject to more severe risks when it came to supply security. Still, the researchers selected two tests of Asian origin: the human test used by Miriam Bosman and a specialised avian influenza test.

Testing different rapid tests

Five tests made it to the laminar flow cabinet for the first trials. ‘A laminar flow cabinet is an open cabinet with an airflow that ensures a clean work environment,’ Van der Wal explains. At first, we researched rapid tests using virus dilutions – avian influenza from a freezer, diluted with increasing amounts of a buffer substance. The researcher places the tests in a row and, based on strict instructions and using a timer, drops ever weaker dilutions onto the test.’ If a rapid test still yields the correct result even when the virus is highly diluted, its sensitivity is high.

Three tests scored well in this stage of the trials. Clungene, the Chinese rapid test that Miriam Bosman had used earlier, performed best. ‘That is quite interesting. Clungene scored slightly better than tests specifically designed to detect avian influenza.’ For the second phase of the trials, Van der Wal and his colleagues were able to cooperate with a study in which chickens and ducks were infected with avian influenza. ‘We received swabs of the airways and the cloaca, just like those that would be taken at a poultry farm. We used those to perform a second set of trials.’ Clungene once more performed well in these trials.

Less reliable than PCR tests

Although Clungene performs well, it is not better than the golden standard: the PCR test. ‘The far more sensitive PCR test offers definite results, just like it did during the pandemic. That won’t change’, Van der Wal stresses. ‘If we extrapolate the results of the chicken and duck swabs and compare them to the PCR results over the past year and a half, the rapid test has a correct assessment rate of about 90%.’ However, the researcher emphasises, these are lab results, which means the rapid test was studied under ideal circumstances.

To determine the actual reliability of a rapid test, field research is needed. Van der Wal and his colleagues advised the Ministry of LVVN to test Clungene on poultry in a practical setting, parallel to the sampling that is already taking place for PCR testing. ‘The results will likely be different at a farm. While a small line can be recognised quite easily in a well-lit laboratory, this might be harder in the field.’ How hard this is exactly will need to be determined during the field tests.

Prioritising

‘At this time, two pilots are in progress. One is being carried out with chickens by employees of the Dutch Food Safety Authority, and the other with wild birds by employees of WBVR and the Dutch Wildlife Health Center,’ Denise Smit explains. ‘Currently, whenever there is a suspected case of avian influenza, rapid tests are performed in addition to the regular PCR tests. These tests are then compared, and the results are added to a database.’ Smit expects that these studies will run until late 2025. ‘This does depend on the amount of data we can collect, of course. The last outbreak among poultry occurred in December last year.’

If the Clungene rapid test performs well in these field studies, it could supplement the current protocols surrounding avian influenza. ‘It would allow us to prioritise, for example,’ Smit says. ‘If there are lots of suspected cases, an initial round of rapid tests could help determine which farms should be investigated first. Positive rapid tests could mean greater urgency for the PCR tests. In the wild, rapid tests could help determine which birds need to be treated and which birds should be isolated. After all, some animals may show symptoms resembling avian influenza while they actually suffer from a different, treatable disease.

The potential use of rapid tests does not change anything with regard to the existing safety recommendations. ‘Suspicious cases should be reported, and anyone who comes into contact with potentially infected birds should use the proper protective equipment, even if a rapid test took place.’ The PCR will always have the last word.