Species-Agnostic Tools for HPAI H5N1 Antibody and Antigen Detection in Dairy Cows, Chickens, and Humans

Viruses that jump between species are a constant concern for public health, particularly when they move from birds to mammals. One such virus, known as High Pathogenicity Avian Influenza H5N1, has long caused severe illness in bird populations. Recently, however, this virus has begun appearing in unexpected places, including dairy cows and humans. Because the virus can spread silently and infect a wide variety of animals, scientists need reliable ways to track it. The challenge is that different animals produce different biological samples, and traditional tests often require specific tools for each species or rely on dangerous, live viruses to work. To solve this, researchers are looking for a single, flexible method that can detect the virus or the body's immune response to it, regardless of whether the sample comes from a cow, a chicken, or a person.

A team of scientists has developed exactly this kind of flexible tool. They created two new tests designed to work across species without needing to be re-engineered for each animal. One test looks for the virus itself, specifically a protein called the nucleoprotein, which acts as a core building block for the virus. The other test looks for antibodies, which are Y-shaped proteins the immune system creates to fight off an infection. By using a highly sensitive electronic detection system, the researchers built a "sandwich" test to catch the virus protein and a "bridging" test to catch the antibodies. The goal was to see if these tests could accurately identify infections in milk and blood from dairy cows, as well as blood from chickens and humans, using the same basic setup for all of them.

The researchers began by testing milk from dairy herds that were known to have the virus. They found that the new tests worked remarkably well. In milk from infected cows, they detected the viral protein in more than half of the samples, with concentrations reaching levels as high as 20 micrograms per milliliter. They also found antibodies in the milk, indicating the cows' immune systems were fighting back. Interestingly, the two tests told different parts of the story. Some samples had the virus protein but no antibodies, suggesting the cows were in the early stages of infection. Other samples had antibodies but no virus protein, suggesting the cows had already cleared the infection. When the researchers combined the results of both tests, they were able to identify nearly every infected cow, missing only one. None of the milk samples from healthy, uninfected cows tested positive, proving the tests did not falsely flag healthy animals.

The team then turned their attention to blood samples from the same infected cows. Here, they compared their new antibody test against a standard, older method that requires handling live viruses. Their new test found antibodies in every sample where the old method found them, but it also found antibodies in twelve additional samples that the old method had missed. This suggests the new test is more sensitive and can spot infections that the traditional method might overlook. Crucially, the test did not produce false alarms in blood samples from healthy cows, maintaining a high level of accuracy.

To ensure these tools worked beyond mammals, the researchers tested them on chickens. They used blood from birds that had been vaccinated against the virus and compared them to birds that had not. The test correctly identified antibodies in every vaccinated chicken, regardless of which specific vaccine formula was used, while correctly ignoring the unvaccinated birds. This is significant because some of the vaccines used in chickens do not always trigger a strong enough response to be detected by older, standard tests. The new method, however, saw the immune response clearly, showing it could be a powerful tool for monitoring bird populations.

Finally, the team tested the system on humans, a critical step given the risk of the virus spreading to farm workers. They used blood samples from people who had received experimental vaccines and compared them to blood from healthy people with no known exposure. A major hurdle in human testing is that many people have antibodies to a different, common flu virus that can sometimes trick the test into giving a false positive. To solve this, the researchers added a blocking agent to the test that neutralizes these common antibodies. With this blocker in place, the test perfectly separated the vaccinated individuals from the healthy ones. It detected the specific antibodies in the vaccinated group while keeping the results for the healthy group clean and negative.

The work demonstrates that a single, adaptable testing platform can effectively monitor the spread of this virus across different species. By detecting both the virus and the immune response in milk and blood, these tools offer a way to track infections from the moment they start until the animal recovers. The ability to use the same test on cows, chickens, and humans simplifies the process of surveillance, making it easier to understand how the virus moves through different populations. This approach provides a clearer picture of the virus's reach, offering a practical way to protect animal health, the food supply, and human safety without needing complex, species-specific equipment for every new outbreak.