What do COVID, Ebola, Hepatitis C, Influenza and Rabies all have in common? Well, they are all viruses (and not our friends). But what exactly is a virus and how does it work to infect a host (you!)?
A virus is a tiny, infectious particle that can reproduce only by infecting cells in larger living things such as animals or plants. Although they can reproduce and evolve, they are not considered living things. Viruses take over the host cell (think of the pirates boarding Tom Hank's ship in 'Captain Phillips' - "look at me, I'm the Captain now"). It hijacks the cell's machinery to make more viruses, basically reprogramming the cell to become a virus factory. It does this in 5 steps.
Attachment: The virus finds the host cell and binds to it, using specially shaped 'receptor molecules' on the cell surface.
Entry: The virus (or sometimes just its genetic material - its version of DNA) enters the cell.
Genome replication: The cell machinery is hijacked to make copies of the virus' genetic material. Like an evil factory line!
Assembly: New virus particles are assembled using the newly created genetic material.
Release: These new viral minions are released into the host, sometimes by bursting from the host cell and killing it. These new virus particles then go on to infect more cells and continue the cycle.
Fortunately, the body is usually able to fight the virus using antibodies which attach to the virus and mark it as an invader. This allows white blood cells to annihilate the virus by engulfing and destroying it. Delightful!
It's important to note that even though they can both make us sick, bacteria and viruses are very different. Bacteria are small and single-celled, but unlike viruses they are living organisms that do not depend on a host cell to reproduce. Because of these differences, bacterial and viral infections are treated very differently. For instance,antibiotics are only helpful against bacteria, not viruses. We rely on our own immune response to fight off most viruses so our only real defence is a vaccination that helps our immune system to get ready when a virus invades so it is destroyed before it can make us poorly.