by Peter Kasson, Professor of Molecular Physiology and Biomedical Engineering, University of Virginia
COVID-19, flu, mpox, noroviral diarrhea: How do the viruses that cause these diseases actually infect you?
Viruses cannot replicate on their own, so they must infect cells in your body to make more copies of themselves. The life cycle of a virus can thus be roughly described as: get inside a cell, make more virus, get out, repeat.
Getting inside a cell, or viral entry, is the part of the cycle that most vaccines target, as well as a key barrier for viruses jumping from one species to another. My lab and many others study this process to better anticipate and combat emerging viruses.
How viruses enter cells
Different viruses travel into the body in various ways – via airborne droplets, on food, through contact with mucous membranes or through injection. They typically first infect host cells near their site of entry – the cells lining the respiratory tract for most airborne viruses – then either remain there or spread throughout the body.
After the virus binds to the cell, specific molecules on the cell’s surface or within the cell’s recycling machinery activate viral coat proteins for entry. An example is the SARS-CoV-2 spike that COVID-19 vaccines target. These proteins need to modify the cell membrane to allow the viral genome to get through without killing the cell in the process. Different viruses use different tricks for this, but most work like cellular secretion – how cells release materials into their environment – in reverse. Specialized viral proteins help merge the membranes of the virus and the cell together and release the viral core into the interior of the cell.