An alpha-coronavirus capable of entering human cells has been identified in African heart-nosed bats (Cardioderma cor). This virus uses the CEACAM6 protein, which is widely present in human lungs, increasing the likelihood of animal-to-human transmission.

The Role of CEACAM6 Protein

CEACAM6 is found in human lungs more frequently than classic coronavirus receptors and is also present in the intestines. The highest concentration of CEACAM6 is observed in goblet cells of the bronchi and in alveolocytes—cells that are the first to interact with respiratory infections. Additionally, CEACAM6 facilitates the attachment and development of infections caused by Escherichia coli in Crohn's disease, as well as by the fungus Candida albicans.

Study of Viral Proteins

During the research, 40 samples of alpha-coronavirus spike proteins—the proteins that allow the virus to attach to cells—were analyzed. Only the KY43 strain was able to infect human lung and intestinal cells. Using protein interaction analysis and RNA interference methods, it was confirmed that the virus specifically binds to CEACAM6. Removing this protein blocked infection, while adding artificial CEACAM6 made infection possible again.

Structural Features of the Interaction

X-ray structural analysis showed that the region of the virus responsible for cell attachment envelops one of the CEACAM6 domains, forming a hydrophobic pocket where fat-soluble parts of molecules are located. A similar domain is used by mouse hepatitis beta-coronaviruses (MHV), but they bind to a different protein in the family—CEACAM1.

Distribution and Evolution of the Virus

Blood analysis of 368 residents from Kenya’s Tana River and Taita-Taveta counties, where heart-nosed bats live, showed no signs of active virus transmission to humans. Only isolated cases of elevated antibody levels were found, likely due to cross-reactions with other coronaviruses. Related viruses that bind to CEACAM6 have been found not only in Kenya but also in Russia and China. Genetic analysis revealed that the ability to bind to CEACAM6 arose independently at least twice in different evolutionary lineages, indicating a high potential for this group of viruses to adapt to humans.

Potential Risks and Importance for Monitoring

Currently, only African virus isolates can recognize human CEACAM6. Asian variants use the bat version of CEACAM6, but not the human one. However, changes in just a few amino acids of the spike protein could expand the range of hosts. This highlights the need to consider not only classic receptors when monitoring zoonotic threats.