On Jul. 6, 2023, University of Illinois Urbana-Champaign researchers reported they can detect exposure to the SARS-CoV-2 virus in any animal species. The new coronavirus test focuses on antibodies against a protein, called the N-protein, that is embedded in the virus’s nucleocapsid – a structure made up of proteins and nucleic acids contained within a viral membrane.

The virus that causes COVID-19 in humans also infects a variety of animals, said University of Illinois Urbana-Champaign pathobiology professor and virologist Ying Fang, who led the new research. So far, the virus has been detected in cats, dogs, rodents, deer, apes and a variety of farm and zoo animals. The virus also mutates in these hosts, potentially leading to new variants that can endanger their – and human – health.

The new coronavirus test focuses on antibodies against a protein, called the N-protein, that is embedded in the virus’s nucleocapsid – a structure made up of proteins and nucleic acids contained within a viral membrane. The N-protein makes a better target than the membrane-bound viral proteins that are usually used in tests for antibody responses, Fang said.

The team used an N-protein-based blocking ELISA protocol for their test. This method involves coating an ELISA plate with the N-protein, then adding a serum sample of whatever animal is being tested. If the animal has been infected with the coronavirus, its serum will contain anti-N-protein antibodies, which will bind to the N-protein-coated plate. The scientists then wash the plate and add a secondary biotin-tagged monoclonal antibody that targets the N-protein.

If the animal is positive for coronavirus infection, its antibodies will block the secondary antibodies from binding to the N-protein. If the animal has not been infected, the monoclonal antibodies will attach to the coated plate and generate a color signal when specific chemicals are added to the plate.

The researchers validated their test using samples from various animals with known SARS-CoV-2 infection status, finding the tests had more than 97% sensitivity and 98% specificity. Further tests in domestic cats showed that the assay was able to detect infection within seven days of exposure to the virus.

The development of accurate cross-species coronavirus tests provides a useful tool for SARS-CoV-2 field surveillance in animal populations, helping scientists identify potential new animal reservoirs to prevent future disease outbreaks, Fang said.