Rapid tests bird flu support PCR analysis

Avian influenza is caused by an influenza virus. The disease occurs in both wild and domestic birds in the Netherlands. Diagnostics at Wageningen Bioveterinary Research (WBVR, part of Wageningen University & Research) for detection of genetic material of avian flu is done with PCR tests. A potentially deployable rapid test can provide authorities with an initial indication to support clinical signs in birds. For this, however, a rapid test must meet specific requirements. Commissioned by the Ministry of Agriculture, Nature and Food Quality (LNV), WBVR examined a selection of user-friendly rapid tests for influenza virus for sensitivity and specificity.

Demonstrating virus

In a first study, rapid tests were used to demonstrate influenza virus in laboratory samples. For this purpose, samples with different virus dilutions of the H5N1 influenza virus were used. From this study, rapid tests were selected that met pre-established criteria and ultimately came out the most sensitive. “A tricky issue with all rapid tests is that low amounts of virus results in very light-coloured lines on the rapid test,” said the researchers. When used on site, weak lines can go unseen while the samples are still positive in PCR.

In the laboratory, the three most sensitive rapid tests were found to detect all influenza viruses studied. In this study, 16 H subtypes were tested, including the high- and low-pathogenic subtypes H5 and H7. “However, the tests do not distinguish between the subtypes,” the researchers stress.

PCR versus rapid test

The sensitivity and specificity of three rapid tests from the laboratory study were also tested with samples from infected poultry. In infected chickens, the best rapid test matched the PCR result in 93 per cent of cases. In uninfected chickens, the rapid test was correctly negative in 94 per cent of cases.

PCR results of samples positive with the most sensitive rapid test, were compared with PCR results of positive poultry samples from the field. The comparison showed that about 90 per cent of PCR-positive field samples would be positive in a rapid test.

Conditions

The WBVR study shows that rapid tests can detect bird flu in many cases, but are less reliable than PCR tests. As a result of the study conducted, the Ministry of Agriculture, Nature and Food Quality (LNV) is now committed to collecting more information on the use of the rapid test in the field. “For example, the rapid tests do not distinguish between subtypes of influenza. Additional diagnostics, such as PCR, must always be used for this. Furthermore, the rapid test was not always found to give the correct result in the study. The use of rapid tests should therefore be subject to clear conditions by the authorities,” according to the WBVR researchers.